postgrpc

https://docs.rs/postgrpc/0.1.2/postgrpc/
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### Asserting Option values in examples

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Demonstrates basic assertion checks for Option values.

```rust
assert_eq!(res, None);
assert_eq!(shared, 6);
```

--------------------------------

### Implementing Connection for tokio_postgres::Client

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/trait.Connection.html

Example implementation of the Connection trait for a PostgreSQL client, mapping database rows to protobuf structs.

```rust
use postgrpc::pools::{Connection, Parameter};
use tonic::{Row, Status};

// implementing a real StructStream (a fallible stream of Structs)
// is an exercise left to the reader
struct StructStream;

impl From<Vec<Row>> for StructStream {
  // also an exercise for the reader
}

#[async_trait]
impl Connection for tokio_postgres::Client {
  type Error = Status;
  type RowStream = StructStream;

  async fn query(
    &self,
    statement: &str,
    parameters: &[Parameter],
  ) -> Result<Self::RowStream, Self::Error> {
    // Parameter implements ToSql, so can be used directly in query()
    let rows: Vec<_> = self
      .query(statement, parameters)
      .await
      .map_error(|error| Status::invalid_argument(error.to_string()))?;

    // it's best to stream rows instead of collecting them into a Vec
    // but this is only meant to be a quick example
     Ok(StructStream::from(rows))
  }

 #[tracing::instrument(skip(self))]
 async fn batch(&self, query: &str) -> Result<(), Self::Error> {
   tracing::trace!("Executing batch query on Connection");
   self.batch_execute(query).await.map_err(|error| Status::invalid_argument(error.to_string()))
   }
}
```

--------------------------------

### Implement a Custom Pool

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/trait.Pool.html

An example implementation of the Pool trait using a BTreeMap and RwLock to manage connections keyed by Uuid.

```rust
use postgrpc::pools::{Pool, Connection};
use std::collections::BTreeMap;
use tokio::sync::RwLock;
use uuid::Uuid;
use tonic::Status;

// a simple connection wrapper
// (implementing postgrpc::Connection is an exercise for the reader)
#[derive(Clone)]
struct MyConnection(Arc<tokio_postgres::Client>);

// a toy pool wrapping a collection of tokio_postgres::Clients
// accessible by unique IDs that are provided by the caller
struct MyPool {
    connections: RwLock<BTreeMap<Uuid, MyConnection>>,
    config: tokio_postgres::config::Config
}

#[postgrpc::async_trait]
impl Pool for MyPool {
    type Key: Uuid;
    type Connection: MyConnection;
    type Error: Status;

    async fn get_connection(&self, key: Self::Key) -> Result<Self::Connection, Self::Error> {
        // get a connection from the pool or store one for later
        let connections = self.connections.read().await;

        match connections.get(&key) {
            Some(connection) => Ok(Arc::clone(connection.0)),
            None => {
                // drop the previous lock on the connections
                drop(connections);

                // connect to the database using the configuration
                let (client, connection) = self
                    .config
                    .connect(tokio_postgres::NoTls)
                    .map_error(|error| Status::internal(error.to_string()))?;

                // spawn the raw connection off onto an executor
                tokio::spawn(async move {
                    if let Err(error) = connection.await {
                        eprintln!("connection error: {}", error);
                    }
                });

                // store a reference to the connection for later
                let connection = MyConnection(Arc::new(client));
                self.connections.write().await.insert(key, connection);

                // return another reference to the connection for use
                Ok(connection)
            }
        }
    }
}
```

--------------------------------

### tonic::server::NamedService Integration

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/index.html

Example of integrating the postgrpc Postgres service into a tonic gRPC server using the deadpool feature.

```APIDOC
## tonic::server::NamedService Integration

### Description
This example demonstrates how to use the `services::postgres` service within a `tonic` server application. It requires the `deadpool` feature to be enabled.

### Implementation
```rust
use postgrpc::{pools::deadpool, services::postgres};
use std::sync::Arc;
use tonic::transport::Server;
use envy::from_env;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
  // create the connection pool from environment variables
  let pool = from_env::<deadpool::Configuration>()?
    .create_pool()
    .map(Arc::new)?;

  // configure and run the tonic server on port 8675
  Server::builder()
    .add_service(services::postgres::new(pool))
    .serve(([127, 0, 0, 1], 8675).into())
    .await?;

  Ok(())
}
```
```

--------------------------------

### Integrate postgrpc with tonic

Source: https://docs.rs/postgrpc

Demonstrates using the deadpool feature to integrate a Postgres service into a tonic server.

```rust
use postgrpc::{pools::deadpool, services::postgres};
use std::sync::Arc;
use tonic::transport::Server;
// deadpool::Configuration implements serde::Deserialize,
// so envy can be used to deserialize it from environment variables
use envy::from_env;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
  // create the connection pool from environment variables
  let pool = from_env::<deadpool::Configuration>()?
    .create_pool()
    .map(Arc::new)?;

  // configure and run the tonic server on port 8675
  Server::builder()
    .add_service(services::postgres::new(pool))
    .serve(([127, 0, 0, 1], 8675).into())
    .await?;

  Ok(())
}
```

--------------------------------

### pub fn new<P>(pool: Arc<P>) -> HealthServer<Health<P>>

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/health/fn.new.html

Initializes a new Health service instance. This function requires the 'health' crate feature to be enabled.

```APIDOC
## Function: new

### Description
Creates a new Health service from a connection pool. This function is used to instantiate the health check service for the application.

### Signature
`pub fn new<P>(pool: Arc<P>) -> HealthServer<Health<P>>`

### Constraints
- `P: Pool + 'static`
- `P::Key: Hash + Eq + Default + Clone`

### Requirements
- Available on crate feature `health` only.
```

--------------------------------

### Initialize TransactionServer

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/fn.new.html

Creates a new Transaction service instance from a connection pool. Requires the transaction feature flag to be enabled.

```rust
pub fn new<P>(pool: Arc<P>) -> TransactionServer<Transaction<P>>
where
    P: Pool + 'static,
    P::Key: FromRequest + Hash + Eq + Clone,
```

--------------------------------

### Pool::begin

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/transaction/struct.Pool.html

Begins a transaction and stores the associated connection in the cache.

```APIDOC
## pub async fn begin(&self, key: P::Key) -> Result<Uuid, Error<...>>

### Description
Begins a transaction, storing the associated connection in the cache for the provided key.
```

--------------------------------

### CloneToUninit Implementation

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.BeginResponse.html

Experimental nightly-only API for performing copy-assignment to uninitialized memory.

```rust
unsafe fn clone_to_uninit(&self, dest: *mut u8)
```

--------------------------------

### Pool::new

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/transaction/struct.Pool.html

Initializes a new shared transaction pool.

```APIDOC
## pub fn new(pool: Arc<P>) -> Self

### Description
Initializes a new shared transaction pool wrapping a lower-level Pool implementation.
```

--------------------------------

### Create a new Key

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/transaction/struct.Key.html

Constructor for creating a new Key instance by pairing a connection pool key with a unique transaction ID.

```rust
pub fn new(key: K, transaction_id: Uuid) -> Self
```

--------------------------------

### Using Option::and

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns None if the option is None, otherwise returns the provided option.

```rust
let x = Some(2);
let y: Option<&str> = None;
assert_eq!(x.and(y), None);

let x: Option<u32> = None;
let y = Some("foo");
assert_eq!(x.and(y), None);

let x = Some(2);
let y = Some("foo");
assert_eq!(x.and(y), Some("foo"));

let x: Option<u32> = None;
let y: Option<&str> = None;
assert_eq!(x.and(y), None);
```

--------------------------------

### Calculate Product of Option Values

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Demonstrates using the product method on an iterator of Option values, returning None if any element is None.

```rust
let nums = vec!["5", "10", "1", "2"];
let total: Option<usize> = nums.iter().map(|w| w.parse::<usize>().ok()).product();
assert_eq!(total, Some(100));
let nums = vec!["5", "10", "one", "2"];
let total: Option<usize> = nums.iter().map(|w| w.parse::<usize>().ok()).product();
assert_eq!(total, None);
```

--------------------------------

### batch

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/deadpool/struct.Client.html

Runs a set of SQL statements using the simple query protocol.

```APIDOC
## fn batch(&self, query: &str) -> Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send + '_>>

### Description
Runs a set of SQL statements using the simple query protocol.

### Parameters
- **query** (&str) - The SQL query string to execute.

### Returns
- **Result<(), Self::Error>** - A future resolving to unit on success or an error.
```

--------------------------------

### Initialize Postgres Service

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/postgres/fn.new.html

Creates a new Postgres service instance from a connection pool wrapped in an Arc. The pool must implement the Pool trait and its key must satisfy the FromRequest trait.

```rust
pub fn new<P>(pool: Arc<P>) -> PostgresServer<Postgres<P>>
where
    P: Pool + 'static,
    P::Key: FromRequest,
```

--------------------------------

### create_pool

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/deadpool/struct.Configuration.html

Creates a new pool instance from the current configuration settings.

```APIDOC
## pub fn create_pool(self) -> Result<Pool, Error>

### Description
Creates a new `Pool` instance using the settings defined in the `Configuration` struct.

### Returns
- **Result<Pool, Error>** - Returns a `Pool` on success, or an `Error` if the pool creation fails.
```

--------------------------------

### Initialize Health Service

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/health/fn.new.html

Creates a new Health service instance from a connection pool. Requires the health feature flag to be enabled.

```rust
pub fn new<P>(pool: Arc<P>) -> HealthServer<Health<P>>
where
    P: Pool + 'static,
    P::Key: Hash + Eq + Default + Clone,
```

--------------------------------

### Iterating over an Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Demonstrates using iter_mut on an Option.

```rust
let mut x: Option<u32> = None;
assert_eq!(x.iter_mut().next(), None);
```

--------------------------------

### Map Option value

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Demonstrates mapping an Option value to a new value.

```rust
let x: Option<&str> = None;
assert_eq!(x.map(|s| s.len()), None);
```

--------------------------------

### Default Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns a None value for an Option.

```rust
let opt: Option<u32> = Option::default();
assert!(opt.is_none());
```

--------------------------------

### Implement FromRequest for Role

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/trait.FromRequest.html

Implementation of FromRequest for the Role type, requiring the role-header feature.

```rust
impl FromRequest for Role
Available on crate feature`role-header` only.
Source§
    type Error = Status
```

--------------------------------

### Using Option::or

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns the option if it contains a value, otherwise returns the provided option.

```rust
let x = Some(2);
let y = None;
assert_eq!(x.or(y), Some(2));

let x = None;
let y = Some(100);
assert_eq!(x.or(y), Some(100));

let x = Some(2);
let y = Some(100);
assert_eq!(x.or(y), Some(2));

let x: Option<u32> = None;
let y = None;
assert_eq!(x.or(y), None);
```

--------------------------------

### Using Option::xor

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns Some if exactly one of the options is Some.

```rust
let x = Some(2);
let y: Option<u32> = None;
assert_eq!(x.xor(y), Some(2));

let x: Option<u32> = None;
let y = Some(2);
assert_eq!(x.xor(y), Some(2));

let x = Some(2);
let y = Some(2);
assert_eq!(x.xor(y), None);

let x: Option<u32> = None;
let y: Option<u32> = None;
assert_eq!(x.xor(y), None);
```

--------------------------------

### Convert to Reference

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Converts Option<T> to Option<&T>.

```rust
let text: Option<String> = Some("Hello, world!".to_string());
// First, cast `Option<String>` to `Option<&String>` with `as_ref`,
// then consume *that* with `map`, leaving `text` on the stack.
let text_length: Option<usize> = text.as_ref().map(|s| s.len());
println!("still can print text: {text:?}");
```

--------------------------------

### fn get_connection

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/trait.Pool.html

Retrieves a connection from the pool based on the provided key. This method is asynchronous and returns a connection or an error.

```APIDOC
## fn get_connection

### Description
Retrieves a single connection from the pool using a specified key. The key allows the pool to manage connection isolation and preparation logic internally.

### Signature
`fn get_connection<'life0, 'async_trait>(&'life0 self, key: Self::Key) -> Pin<Box<dyn Future<Output = Result<Self::Connection, Self::Error>> + Send + 'async_trait>>`

### Parameters
- **key** (Self::Key) - Required - The key used to identify or fetch the specific connection from the pool.

### Returns
- **Result<Self::Connection, Self::Error>** - A future that resolves to the connection or an error if the connection could not be retrieved.
```

--------------------------------

### From Trait Implementation

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.BeginResponse.html

Returns the argument unchanged.

```rust
fn from(t: T) -> T
```

--------------------------------

### Define Client struct

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/deadpool/struct.Client.html

The definition of the Client struct, which is only available when the deadpool feature is enabled.

```rust
pub struct Client { /* private fields */ }
```

--------------------------------

### Calculate Sum of Option Values

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Demonstrates using the sum method on an iterator of Option values, returning None if any element is None.

```rust
let words = vec!["have", "a", "great", "day"];
let total: Option<usize> = words.iter().map(|w| w.find('a')).sum();
assert_eq!(total, Some(5));
let words = vec!["have", "a", "good", "day"];
let total: Option<usize> = words.iter().map(|w| w.find('a')).sum();
assert_eq!(total, None);
```

--------------------------------

### query

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/deadpool/struct.Client.html

Runs a query parameterized by the Connection’s associated Parameter, returning a RowStream.

```APIDOC
## fn query(&self, statement: &str, parameters: &[Parameter]) -> Pin<Box<dyn Future<Output = Result<Self::RowStream, Self::Error>> + Send + '_>>

### Description
Runs a query parameterized by the Connection’s associated Parameter, returning a RowStream.

### Parameters
- **statement** (&str) - The SQL statement to execute.
- **parameters** (&[Parameter]) - The parameters to bind to the query.

### Returns
- **Result<Self::RowStream, Self::Error>** - A future resolving to a fallible stream of rows returned as protobuf structs or an error.
```

--------------------------------

### Using Option::filter

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Filters the Option based on a predicate.

```rust
fn is_even(n: &i32) -> bool {
    n % 2 == 0
}

assert_eq!(None.filter(is_even), None);
assert_eq!(Some(3).filter(is_even), None);
assert_eq!(Some(4).filter(is_even), Some(4));
```

--------------------------------

### BeginResponse Struct Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.BeginResponse.html

The structure definition for BeginResponse, containing the unique transaction ID.

```rust
pub struct BeginResponse {
    pub id: String,
}
```

--------------------------------

### Implement FromRequest for unit type

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/trait.FromRequest.html

A default implementation of FromRequest for the unit type ().

```rust
impl FromRequest for ()
Source§
    type Error = UnitConversion
Source§
    fn from_request<T>(_: &mut Request<T>) -> Result<Self, Self::Error>
```

--------------------------------

### Expect a value from Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns the contained value or panics with a custom message if the Option is None.

```rust
let x = Some("value");
assert_eq!(x.expect("fruits are healthy"), "value");
```

```rust
let x: Option<&str> = None;
x.expect("fruits are healthy"); // panics with `fruits are healthy`
```

```rust
let item = slice.get(0)
    .expect("slice should not be empty");
```

--------------------------------

### Collecting Option into a Vector

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Shows how to use into_iter to collect the contents of an Option into a Vec.

```rust
let x = Some("string");
let v: Vec<&str> = x.into_iter().collect();
assert_eq!(v, ["string"]);

let x = None;
let v: Vec<&str> = x.into_iter().collect();
assert!(v.is_empty());
```

--------------------------------

### Using Option::and_then

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Chains fallible operations that return an Option.

```rust
fn sq_then_to_string(x: u32) -> Option<String> {
    x.checked_mul(x).map(|sq| sq.to_string())
}

assert_eq!(Some(2).and_then(sq_then_to_string), Some(4.to_string()));
assert_eq!(Some(1_000_000).and_then(sq_then_to_string), None); // overflowed!
assert_eq!(None.and_then(sq_then_to_string), None);
```

```rust
let arr_2d = [["A0", "A1"], ["B0", "B1"]];

let item_0_1 = arr_2d.get(0).and_then(|row| row.get(1));
assert_eq!(item_0_1, Some(&"A1"));

let item_2_0 = arr_2d.get(2).and_then(|row| row.get(0));
assert_eq!(item_2_0, None);
```

--------------------------------

### get_connection

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/deadpool/struct.Pool.html

Retrieves a single connection from the pool using a specified key.

```APIDOC
## fn get_connection

### Description
Get a single connection from the pool using some key.

### Signature
`fn get_connection<'life0, 'async_trait>(&'life0 self, key: Self::Key) -> Pin<Box<dyn Future<Output = Result<Self::Connection, Self::Error>> + Send + 'async_trait>>`

### Parameters
- **key** (Self::Key) - Required - The key by which connections are selected from the Pool.
```

--------------------------------

### Zip two Options with a function

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Combines two options using a provided function if both are Some. Requires the option_zip feature.

```rust
#![feature(option_zip)]

#[derive(Debug, PartialEq)]
struct Point {
    x: f64,
    y: f64,
}

impl Point {
    fn new(x: f64, y: f64) -> Self {
        Self { x, y }
    }
}

let x = Some(17.5);
let y = Some(42.7);
```

--------------------------------

### Check None or Predicate

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Checks if an option is None or matches a predicate.

```rust
let x: Option<u32> = Some(2);
assert_eq!(x.is_none_or(|x| x > 1), true);

let x: Option<u32> = Some(0);
assert_eq!(x.is_none_or(|x| x > 1), false);

let x: Option<u32> = None;
assert_eq!(x.is_none_or(|x| x > 1), true);

let x: Option<String> = Some("ownership".to_string());
assert_eq!(x.as_ref().is_none_or(|x| x.len() > 1), true);
println!("still alive {:?}", x);
```

--------------------------------

### Map Option or default value

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Maps an Option to a value, returning the type's default if None.

```rust
let x: Option<&str> = Some("hi");
let y: Option<&str> = None;

assert_eq!(x.map_or_default(|x| x.len()), 2);
assert_eq!(y.map_or_default(|y| y.len()), 0);
```

--------------------------------

### Using Option::get_or_insert

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Inserts a value if the option is None, then returns a mutable reference.

```rust
let mut x = None;

{
    let y: &mut u32 = x.get_or_insert(5);
    assert_eq!(y, &5);

    *y = 7;
}
```

--------------------------------

### Take value from Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Extracts the value from the option, leaving None in its place.

```rust
let mut x = Some(2);
let y = x.take();
assert_eq!(x, None);
assert_eq!(y, Some(2));

let mut x: Option<u32> = None;
let y = x.take();
assert_eq!(x, None);
assert_eq!(y, None);
```

--------------------------------

### Check Some Value with Predicate

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Checks if an option is Some and matches a predicate.

```rust
let x: Option<u32> = Some(2);
assert_eq!(x.is_some_and(|x| x > 1), true);

let x: Option<u32> = Some(0);
assert_eq!(x.is_some_and(|x| x > 1), false);

let x: Option<u32> = None;
assert_eq!(x.is_some_and(|x| x > 1), false);

let x: Option<String> = Some("ownership".to_string());
assert_eq!(x.as_ref().is_some_and(|x| x.len() > 1), true);
println!("still alive {:?}", x);
```

--------------------------------

### Implement role-header interceptor

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/index.html

Requires the 'role-header' feature enabled. This interceptor is used with tonic services to extract Postgres roles from requests.

```rust
// requires the "role-header" feature
use postgrpc::{extensions, pools::Pool, services};
use tonic::codegen::InterceptedService;

// somewhere in a tonic app
services::postgres::with_interceptor(pool, extensions::role_header::interceptor)
```

--------------------------------

### Using Option::insert

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Inserts a value into the option and returns a mutable reference.

```rust
let mut opt = None;
let val = opt.insert(1);
assert_eq!(*val, 1);
assert_eq!(opt.unwrap(), 1);
let val = opt.insert(2);
assert_eq!(*val, 2);
*val = 3;
assert_eq!(opt.unwrap(), 3);
```

--------------------------------

### Zip two Options into a tuple

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Combines two options into a single option containing a tuple if both are Some.

```rust
let x = Some(1);
let y = Some("hi");
let z = None::<u8>;

assert_eq!(x.zip(y), Some((1, "hi")));
assert_eq!(x.zip(z), None);
```

--------------------------------

### Map Option or default

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns a default value if None, or applies a function to the contained value.

```rust
let x = Some("foo");
assert_eq!(x.map_or(42, |v| v.len()), 3);

let x: Option<&str> = None;
assert_eq!(x.map_or(42, |v| v.len()), 42);
```

--------------------------------

### Into Trait Implementation

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.BeginResponse.html

Performs a conversion into another type using the From implementation.

```rust
fn into(self) -> U
```

--------------------------------

### Iterate over Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns an iterator over the contained value.

```rust
let x = Some(4);
assert_eq!(x.iter().next(), Some(&4));

let x: Option<u32> = None;
assert_eq!(x.iter().next(), None);
```

--------------------------------

### Map Option or else

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Computes a default value using a function if None, or applies a function to the contained value.

```rust
let k = 21;

let x = Some("foo");
assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 3);

let x: Option<&str> = None;
assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 42);
```

```rust
let v: u64 = std::env::args()
   .nth(1)
   .map_or_else(|| std::fs::read_to_string("/etc/someconfig.conf"), Ok)?
   .parse()?;
```

--------------------------------

### pub fn interceptor(request: Request<()>) -> Result<Request<()>, Status>

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/fn.interceptor.html

Interceptor function for collecting user ROLEs from tonic::Request headers.

```APIDOC
## Function: interceptor

### Description
Interceptor function for collecting user `ROLE`s from `tonic::Request` headers. This function is available only when the `role-header` crate feature is enabled.

### Signature
`pub fn interceptor(request: Request<()>) -> Result<Request<()>, Status>`

### Parameters
- **request** (Request<()>) - The incoming tonic request containing headers to be processed.

### Returns
- **Result<Request<()>, Status>** - Returns the original request if successful, or a tonic::Status error if the interception fails.
```

--------------------------------

### Convert Value to Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Moves a value into a new Some variant.

```rust
let o: Option<u8> = Option::from(67);

assert_eq!(Some(67), o);
```

--------------------------------

### Check for None Value

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Checks if an option is None.

```rust
let x: Option<u32> = Some(2);
assert_eq!(x.is_none(), false);

let x: Option<u32> = None;
assert_eq!(x.is_none(), true);
```

--------------------------------

### Unwrap with default value

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns the contained value or a provided default value.

```rust
assert_eq!(Some("car").unwrap_or("bike"), "car");
assert_eq!(None.unwrap_or("bike"), "bike");
```

--------------------------------

### Reduce Options

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Reduces two options into one using a provided function if both are Some.

```rust
#![feature(option_reduce)]

let s12 = Some(12);
let s17 = Some(17);
let n = None;
let f = |a, b| a + b;

assert_eq!(s12.reduce(s17, f), Some(29));
assert_eq!(s12.reduce(n, f), Some(12));
assert_eq!(n.reduce(s17, f), Some(17));
assert_eq!(n.reduce(n, f), None);
```

--------------------------------

### with_interceptor function signature

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/postgres/fn.with_interceptor.html

Defines the function signature for creating an intercepted Postgres service.

```rust
pub fn with_interceptor<P, I>(
    pool: Arc<P>,
    interceptor: I,
) -> InterceptedService<PostgresServer<Postgres<P>>, I>
where
    P: Pool + 'static,
    P::Key: FromRequest,
    I: Interceptor,
```

--------------------------------

### FromRef Trait Implementation

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.BeginResponse.html

Converts to this type from a reference to the input type.

```rust
fn from_ref(input: &T) -> T
```

--------------------------------

### Unwrap an Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns the contained value, panicking if the Option is None. Prefer safer alternatives like pattern matching or unwrap_or.

```rust
let x = Some("air");
assert_eq!(x.unwrap(), "air");
```

```rust
let x: Option<&str> = None;
assert_eq!(x.unwrap(), "air"); // fails
```

--------------------------------

### from_request

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Derives a Role value from a tonic::Request. This method is used to extract the Role from incoming gRPC requests.

```APIDOC
## fn from_request<T>(request: &mut Request<T>) -> Result<Self, Self::Error>

### Description
Derive a value from a `tonic::Request`.

### Parameters
- **request** (&mut Request<T>) - Required - The gRPC request to derive the Role from.

### Response
- **Result<Self, Self::Error>** - Returns the Role instance on success, or a Status error if the derivation fails.
```

--------------------------------

### Convert to Slice

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns a slice of the contained value or an empty slice.

```rust
assert_eq!(
    [Some(1234).as_slice(), None.as_slice()],
    [&[1234][..], &[][..]],
);
```

```rust
for i in [Some(1234_u16), None] {
    assert_eq!(i.as_ref(), i.as_slice().first());
}
```

--------------------------------

### Using Option::or_else

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns the option if it contains a value, otherwise calls the provided function.

```rust
fn nobody() -> Option<&'static str> { None }
fn vikings() -> Option<&'static str> { Some("vikings") }

assert_eq!(Some("barbarians").or_else(vikings), Some("barbarians"));
assert_eq!(None.or_else(vikings), Some("vikings"));
assert_eq!(None.or_else(nobody), None);
```

--------------------------------

### Transform Option to Result with closure

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Converts an Option to a Result, using a closure to generate the error if None.

```rust
let x = Some("foo");
assert_eq!(x.ok_or_else(|| 0), Ok("foo"));

let x: Option<&str> = None;
assert_eq!(x.ok_or_else(|| 0), Err(0));
```

--------------------------------

### Replace value in Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Replaces the current value with a new one and returns the old value.

```rust
let mut x = Some(2);
let old = x.replace(5);
assert_eq!(x, Some(5));
assert_eq!(old, Some(2));

let mut x = None;
let old = x.replace(3);
assert_eq!(x, Some(3));
assert_eq!(old, None);
```

--------------------------------

### Use into_flat_iter

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Transforms an optional iterator into an iterator.

```rust
#![feature(option_into_flat_iter)]

let o1 = Some([1, 2]);
let o2 = None::<&[usize]>;

assert_eq!(o1.into_flat_iter().collect::<Vec<_>>(), [1, 2]);
assert_eq!(o2.into_flat_iter().collect::<Vec<_>>(), Vec::<&usize>::new());
```

--------------------------------

### Apply async_trait attribute

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/attr.async_trait.html

Use this attribute macro to enable async trait implementations.

```rust
#[async_trait]
```

--------------------------------

### Map an Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Applies a function to the contained value if Some, otherwise returns None.

```rust
let maybe_some_string = Some(String::from("Hello, World!"));
// `Option::map` takes self *by value*, consuming `maybe_some_string`
let maybe_some_len = maybe_some_string.map(|s| s.len());
assert_eq!(maybe_some_len, Some(13));
```

--------------------------------

### Convert to Mutable Reference

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Converts Option<T> to Option<&mut T>.

```rust
let mut x = Some(2);
match x.as_mut() {
    Some(v) => *v = 42,
    None => {},
}
assert_eq!(x, Some(42));
```

--------------------------------

### Check for Some Value

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Checks if an option contains a value.

```rust
let x: Option<u32> = Some(2);
assert_eq!(x.is_some(), true);

let x: Option<u32> = None;
assert_eq!(x.is_some(), false);
```

--------------------------------

### Key Struct Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/transaction/struct.Key.html

The definition of the Key struct, which requires the generic type K to implement Hash and Eq.

```rust
pub struct Key<K>
where
    K: Hash + Eq,
{ /* private fields */ }
```

--------------------------------

### Inspect Option value

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Executes a function with a reference to the contained value if it is Some.

```rust
let list = vec![1, 2, 3];

// prints "got: 2"
let x = list
    .get(1)
    .inspect(|x| println!("got: {x}"))
    .expect("list should be long enough");

// prints nothing
list.get(5).inspect(|x| println!("got: {x}"));
```

--------------------------------

### Collect Iterator of Options

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Collects an iterator of Options into an Option of a collection, returning None if any element is None.

```rust
let items = vec![0_u16, 1, 2];

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| x.checked_add(1))
    .collect();

assert_eq!(res, Some(vec![1, 2, 3]));
```

```rust
let items = vec![2_u16, 1, 0];

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| x.checked_sub(1))
    .collect();

assert_eq!(res, None);
```

```rust
let items = vec![3_u16, 2, 1, 10];

let mut shared = 0;

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| { shared += x; x.checked_sub(2) })
    .collect();
```

--------------------------------

### QueryRequest Struct Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/postgres/struct.QueryRequest.html

The structure definition for QueryRequest, consisting of a statement string and a vector of values.

```rust
pub struct QueryRequest {
    pub statement: String,
    pub values: Vec<Value>,
}
```

--------------------------------

### IntoRequest Trait Implementation

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.BeginResponse.html

Wraps the input message into a tonic Request.

```rust
fn into_request(self) -> Request<T>
```

--------------------------------

### Transform Option to Result

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Converts an Option to a Result, using a provided error value if None.

```rust
let x = Some("foo");
assert_eq!(x.ok_or(0), Ok("foo"));

let x: Option<&str> = None;
assert_eq!(x.ok_or(0), Err(0));
```

--------------------------------

### Instrument Trait Implementation

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.BeginResponse.html

Provides methods to instrument types with tracing spans.

```rust
fn instrument(self, span: Span) -> Instrumented<Self>
fn in_current_span(self) -> Instrumented<Self>
```

--------------------------------

### Postgres Struct Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/postgres/struct.Postgres.html

The primary definition of the Postgres struct, which is generic over a pool type P.

```rust
pub struct Postgres<P> { /* private fields */ }
```

--------------------------------

### Conditionally take value from Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Takes the value out of the option only if the provided predicate returns true.

```rust
let mut x = Some(42);

let prev = x.take_if(|v| if *v == 42 {
    *v += 1;
    false
} else {
    false
});
assert_eq!(x, Some(43));
assert_eq!(prev, None);

let prev = x.take_if(|v| *v == 43);
assert_eq!(x, None);
assert_eq!(prev, Some(43));
```

--------------------------------

### with_interceptor function signature

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/fn.with_interceptor.html

Defines the function signature for creating an intercepted transaction service. Requires the transaction feature flag to be enabled.

```rust
pub fn with_interceptor<P, I>(
    pool: Arc<P>,
    interceptor: I,
) -> InterceptedService<TransactionServer<Transaction<P>>, I>
where
    P: Pool + 'static,
    P::Key: FromRequest + Hash + Eq + Clone,
    I: Interceptor,
```

--------------------------------

### Unwrap with closure

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns the contained value or computes a default value using a closure.

```rust
let k = 10;
assert_eq!(Some(4).unwrap_or_else(|| 2 * k), 4);
assert_eq!(None.unwrap_or_else(|| 2 * k), 20);
```

--------------------------------

### Insert default value into Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Inserts the default value if the option is None and returns a mutable reference to the value.

```rust
let mut x = None;

{
    let y: &mut u32 = x.get_or_insert_default();
    assert_eq!(y, &0);

    *y = 7;
}

assert_eq!(x, Some(7));
```

--------------------------------

### StructStream Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/deadpool/struct.StructStream.html

The definition of the StructStream struct.

```rust
pub struct StructStream { /* private fields */ }
```

--------------------------------

### Connection Trait Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/trait.Connection.html

The core trait definition requiring Send and Sync, defining associated types for row streams and errors, and specifying query and batch methods.

```rust
pub trait Connection: Send + Sync {
    type RowStream: TryStream<Ok = Struct, Error = Self::Error> + Send + Sync;
    type Error: Error + Into<Status> + Send + Sync;

    // Required methods
    fn query<'life0, 'life1, 'life2, 'async_trait>(
        &'life0 self,
        statement: &'life1 str,
        parameters: &'life2 [Parameter],
    ) -> Pin<Box<dyn Future<Output = Result<Self::RowStream, Self::Error>> + Send + 'async_trait>>
       where Self: 'async_trait,
             'life0: 'async_trait,
             'life1: 'async_trait,
             'life2: 'async_trait;
    fn batch<'life0, 'life1, 'async_trait>(
        &'life0 self,
        query: &'life1 str,
    ) -> Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send + 'async_trait>>
       where Self: 'async_trait,
             'life0: 'async_trait,
             'life1: 'async_trait;
}
```

--------------------------------

### Parameter struct definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/struct.Parameter.html

The definition of the Parameter struct as a private newtype wrapper.

```rust
pub struct Parameter(/* private fields */);
```

--------------------------------

### Convert Option to mutable slice

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Use as_mut_slice to obtain a mutable slice of the contained value, returning an empty slice if None.

```rust
assert_eq!(
    [Some(1234).as_mut_slice(), None.as_mut_slice()],
    [&mut [1234][..], &mut [][..]],
);
```

```rust
let mut x = Some(1234);
x.as_mut_slice()[0] += 1;
assert_eq!(x, Some(1235));
```

```rust
assert_eq!(Some(123).as_mut_slice().first_mut(), Some(&mut 123))
```

--------------------------------

### TryFrom Trait Implementation

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.BeginResponse.html

Performs a fallible conversion from another type.

```rust
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
```

--------------------------------

### TransactionQueryRequest Struct Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.TransactionQueryRequest.html

The primary data structure for transaction queries, containing the statement, values, and ID fields.

```rust
pub struct TransactionQueryRequest {
    pub statement: String,
    pub values: Vec<Value>,
    pub id: String,
}
```

--------------------------------

### TryInto Trait Implementation

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.BeginResponse.html

Performs a fallible conversion into another type.

```rust
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
```

--------------------------------

### Define Role Type Alias

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

The primary definition of the Role type alias.

```rust
pub type Role = Option<String>;
```

--------------------------------

### Represent Role Enum Structure

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

The underlying enum structure for the Role type.

```rust
pub enum Role {
    None,
    Some(String),
}
```

--------------------------------

### Conditionally insert value using Try trait

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Inserts a value if the option is None, provided the closure returns a successful result. Requires the option_get_or_try_insert_with feature.

```rust
#![feature(option_get_or_try_insert_with)]
let mut o1: Option<u32> = None;
let mut o2: Option<u8> = None;

let number = "12345";

assert_eq!(o1.get_or_try_insert_with(|| number.parse()).copied(), Ok(12345));
assert!(o2.get_or_try_insert_with(|| number.parse()).is_err());
assert_eq!(o1, Some(12345));
assert_eq!(o2, None);
```

--------------------------------

### Define the Pool Trait

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/trait.Pool.html

The core trait definition requiring Send and Sync bounds, associated types for keys, connections, and errors, and the get_connection method.

```rust
pub trait Pool: Send + Sync {
    type Key: Debug + Send + Sync;
    type Connection: Connection;
    type Error: Error + From<<Self::Connection as Connection>::Error> + Into<Status> + Send + Sync;

    // Required method
    fn get_connection<'life0, 'async_trait>(
        &'life0 self,
        key: Self::Key,
    ) -> Pin<Box<dyn Future<Output = Result<Self::Connection, Self::Error>> + Send + 'async_trait>>
       where Self: 'async_trait,
             'life0: 'async_trait;
}
```

--------------------------------

### WithSubscriber Trait Implementation

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.BeginResponse.html

Attaches a subscriber to the type for tracing purposes.

```rust
fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
fn with_current_subscriber(self) -> WithDispatch<Self>
```

--------------------------------

### interceptor

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/index.html

An interceptor function used to collect user roles from tonic::Request headers.

```APIDOC
## interceptor

### Description
Interceptor function for collecting user `ROLE`s from `tonic::Request` headers. This function is available when the `role-header` feature is enabled.

### Signature
`pub fn interceptor<T>(request: tonic::Request<T>) -> Result<tonic::Request<T>, tonic::Status>`
```

--------------------------------

### Define Pool struct

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/deadpool/struct.Pool.html

The internal structure of the Pool type.

```rust
pub struct Pool { /* private fields */ }
```

--------------------------------

### Define UnitConversion struct

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/struct.UnitConversion.html

The definition of the UnitConversion unit struct.

```rust
pub struct UnitConversion;
```

--------------------------------

### Insert value from closure into Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Computes a value from a closure to insert if the option is None, returning a mutable reference.

```rust
let mut x = None;

{
    let y: &mut u32 = x.get_or_insert_with(|| 5);
    assert_eq!(y, &5);

    *y = 7;
}

assert_eq!(x, Some(7));
```

--------------------------------

### Mutably iterate over Option

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns a mutable iterator over the contained value.

```rust
let mut x = Some(4);
match x.iter_mut().next() {
    Some(v) => *v = 42,
    None => {},
}
assert_eq!(x, Some(42));
```

--------------------------------

### CommitRequest Struct Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.CommitRequest.html

The primary structure definition for CommitRequest, containing the transaction ID.

```rust
pub struct CommitRequest {
    pub id: String,
}
```

--------------------------------

### Define the FromRequest trait

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/trait.FromRequest.html

The trait definition requires an associated Error type that can be converted into a tonic::Status.

```rust
pub trait FromRequest
where
    Self: Sized,
{
    type Error: Error + Into<Status>;

    // Required method
    fn from_request<T>(request: &mut Request<T>) -> Result<Self, Self::Error>;
}
```

--------------------------------

### Unwrap with default trait

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns the contained value or the default value for the type if None.

```rust
let x: Option<u32> = None;
let y: Option<u32> = Some(12);

assert_eq!(x.unwrap_or_default(), 0);
assert_eq!(y.unwrap_or_default(), 12);
```

--------------------------------

### Interceptor function signature

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/fn.interceptor.html

The function signature for the interceptor used to process tonic requests.

```rust
pub fn interceptor(request: Request<()>) -> Result<Request<()>, Status>
```

--------------------------------

### Health Struct Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/health/struct.Health.html

The definition of the Health struct, which is generic over a connection pool P.

```rust
pub struct Health<P>
where
    P: Pool,
    P::Key: Hash + Eq + Default + Clone,
{ /* private fields */ }
```

--------------------------------

### Pool::rollback

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/transaction/struct.Pool.html

Rolls back a transaction and removes it from the cache.

```APIDOC
## pub async fn rollback(&self, transaction_id: Uuid, key: P::Key) -> Result<(), Error<...>>

### Description
Removes a transaction from the cache, rolling back all intermediate changes.
```

--------------------------------

### HealthCheckResponse struct definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/health/struct.HealthCheckResponse.html

The primary structure definition for the health check response.

```rust
pub struct HealthCheckResponse {
    pub status: i32,
}
```

--------------------------------

### Transaction Struct Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.Transaction.html

The definition of the Transaction struct, requiring a pool that implements the Pool trait.

```rust
pub struct Transaction<P>
where
    P: Pool,
    P::Key: Hash + Eq + Clone,
{ /* private fields */ }
```

--------------------------------

### Pool::commit

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/transaction/struct.Pool.html

Commits a transaction and removes it from the cache.

```APIDOC
## pub async fn commit(&self, transaction_id: Uuid, key: P::Key) -> Result<(), Error<...>>

### Description
Removes a transaction from the cache, committing its changeset in postgres.
```

--------------------------------

### RollbackRequest Struct Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.RollbackRequest.html

The definition of the RollbackRequest struct containing the transaction ID.

```rust
pub struct RollbackRequest {
    pub id: String,
}
```

--------------------------------

### Define Transaction Struct

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/transaction/struct.Transaction.html

The definition of the Transaction struct, which is generic over a Connection type and contains private fields.

```rust
pub struct Transaction<C>
where
    C: Connection,
{ /* private fields */ }
```

--------------------------------

### HealthCheckRequest struct definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/health/struct.HealthCheckRequest.html

The primary structure definition for HealthCheckRequest containing the service field.

```rust
pub struct HealthCheckRequest {
    pub service: String,
}
```

--------------------------------

### Pool Struct Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/transaction/struct.Pool.html

The definition of the Pool struct, requiring a generic type P that implements the Pool trait.

```rust
pub struct Pool<P>
where
    P: Pool,
    P::Key: Hash + Eq + Clone,
{ /* private fields */ }
```

--------------------------------

### Unwrap without checking

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Returns the contained value without checking for None. Calling on None is undefined behavior.

```rust
let x = Some("air");
assert_eq!(unsafe { x.unwrap_unchecked() }, "air");
```

```rust
let x: Option<&str> = None;
assert_eq!(unsafe { x.unwrap_unchecked() }, "air"); // Undefined behavior!
```

--------------------------------

### Deref Option contents

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Converts an Option to an Option containing a reference to the inner type's target.

```rust
let x: Option<String> = Some("hey".to_owned());
assert_eq!(x.as_deref(), Some("hey"));

let x: Option<String> = None;
assert_eq!(x.as_deref(), None);
```

--------------------------------

### ToOwned Trait Implementation

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/services/transaction/struct.BeginResponse.html

Provides methods for creating owned data from borrowed data.

```rust
fn to_owned(&self) -> T
fn clone_into(&self, target: &mut T)
```

--------------------------------

### Error Enum Definition

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/deadpool/enum.Error.html

The structure of the Error enum used for handling database and pooling operations.

```rust
pub enum Error {
    Params {
        expected: usize,
        actual: usize,
    },
    Pool(PoolError),
    Query(Error),
    Role(Error),
    InvalidJson,
    Create(CreatePoolError),
    Tls(Error),
}
```

--------------------------------

### Define the Error enum

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/pools/transaction/enum.Error.html

The Error enum structure for transaction pool operations, generic over a connection error type C.

```rust
pub enum Error<C>
where
    C: Error + 'static,
{
    Connection(C),
    ConnectionFailure,
    Uninitialized,
}
```

--------------------------------

### Deref Option contents mutably

Source: https://docs.rs/postgrpc/0.1.2/postgrpc/extensions/role_header/type.Role.html

Converts an Option to an Option containing a mutable reference to the inner type's target.

```rust
let mut x: Option<String> = Some("hey".to_owned());
assert_eq!(x.as_deref_mut().map(|x| {
    x.make_ascii_uppercase();
    x
}), Some("HEY".to_owned().as_mut_str()));
```
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