### Create Client and Schema Migration (SQLite)

Source: https://entgo.io/docs/getting-started/index

Opens a connection to a SQLite database in memory and runs the auto-migration tool to create the schema. This example uses a temporary in-memory database.

```go
package main

import (
    "context"
    "log"

    "entdemo/ent"

    _ "github.com/mattn/go-sqlite3"
)

func main() {
    client, err := ent.Open("sqlite3", "file:ent?mode=memory&cache=shared&_fk=1")
    if err != nil {
        log.Fatalf("failed opening connection to sqlite: %v", err)
    }
    defer client.Close()
    // Run the auto migration tool.
    if err := client.Schema.Create(context.Background()); err != nil {
        log.Fatalf("failed creating schema resources: %v", err)
    }
}
```

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

### Install Atlas CLI using cURL

Source: https://entgo.io/docs/getting-started/index

This command installs the latest release of the Atlas CLI tool by downloading and executing the official installation script from a cURL command.

```bash
curl -sSf https://atlasgo.sh | sh

```

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

### Install Atlas CLI using Homebrew

Source: https://entgo.io/docs/getting-started/index

This command installs the latest release of the Atlas CLI tool on macOS using the Homebrew package manager.

```bash
brew install ariga/tap/atlas

```

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

### Pull and Run Atlas Docker Image

Source: https://entgo.io/docs/getting-started/index

This command pulls the latest official Atlas Docker image and then runs it to display the help information, confirming the installation.

```bash
docker pull arigaio/atlas
docker run --rm arigaio/atlas --help

```

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

### Apply Database Migrations with Atlas CLI

Source: https://entgo.io/docs/getting-started/index

These commands use the Atlas CLI to apply generated migration files to a target database. They require the migration directory and the production database URL. Examples are provided for connecting to MySQL, MariaDB, PostgreSQL, and SQLite databases. The command executes the SQL statements contained within the migration files.

```bash
atlas migrate apply \
  --dir "file://ent/migrate/migrations" \
  --url "mysql://root:pass@localhost:3306/example"
```

```bash
atlas migrate apply \
  --dir "file://ent/migrate/migrations" \
  --url "maria://root:pass@localhost:3306/example"
```

```bash
atlas migrate apply \
  --dir "file://ent/migrate/migrations" \
  --url "postgres://postgres:pass@localhost:5432/database?search_path=public&sslmode=disable"
```

```bash
atlas migrate apply \
  --dir "file://ent/migrate/migrations" \
  --url "sqlite://file.db?_fk=1"
```

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

### Query Inverse Edge for Car Owner in Go

Source: https://entgo.io/docs/getting-started/index

This Go code demonstrates how to query the inverse 'owner' edge from a Car object. It first retrieves a user's cars and then iterates through them, querying the 'owner' of each car using `QueryOwner().Only(ctx)` to get the associated user.

```go
func QueryCarUsers(ctx context.Context, a8m *ent.User) error {
    cars, err := a8m.QueryCars().All(ctx)
    if err != nil {
        return fmt.Errorf("failed querying user cars: %w", err)
    }
    // Query the inverse edge.
    for _, c := range cars {
        owner, err := c.QueryOwner().Only(ctx)
        if err != nil {
            return fmt.Errorf("failed querying car %q owner: %w", c.Model, err)
        }
        log.Printf("car %q owner: %q\n", c.Model, owner.Name)
    }
    return nil
}

```

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

### Query Cars for Users in a Specific Group (Ent Go)

Source: https://entgo.io/docs/getting-started/index

This Go function queries for all cars belonging to users within the 'GitHub' group. It demonstrates multi-step traversal starting from the Group entity, filtering by name, querying associated users, and then their cars.

```go
func QueryGithub(ctx context.Context, client *ent.Client) error {
    cars, err := client.Group.
        Query().
        Where(group.Name("GitHub")). // (Group(Name=GitHub),)
        QueryUsers().                // (User(Name=Ariel, Age=30),)
        QueryCars().                 // (Car(Model=Tesla, RegisteredAt=<Time>), Car(Model=Mazda, RegisteredAt=<Time>),)
        All(ctx)
    if err != nil {
        return fmt.Errorf("failed getting cars: %w", err)
    }
    log.Println("cars returned:", cars)
    // Output: (Car(Model=Tesla, RegisteredAt=<Time>), Car(Model=Mazda, RegisteredAt=<Time>),)
    return nil
}

```

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

### Query Cars of a Specific User with Filters (Ent Go)

Source: https://entgo.io/docs/getting-started/index

This Go function retrieves cars associated with the user 'Ariel', excluding cars with the model 'Mazda'. It starts by fetching the user 'Ariel', then traverses through their groups, users, and finally their cars, applying a negation filter on the car model.

```go
func QueryArielCars(ctx context.Context, client *ent.Client) error {
    // Get "Ariel" from previous steps.
    a8m := client.User.
        Query().
        Where(
            user.HasCars(),
            user.Name("Ariel"),
        ).
        OnlyX(ctx)
    cars, err := a8m.                       // Get the groups, that a8m is connected to:
            QueryGroups().                  // (Group(Name=GitHub), Group(Name=GitLab),)
            QueryUsers().                   // (User(Name=Ariel, Age=30), User(Name=Neta, Age=28),)
            QueryCars().                    //
            Where(
                car.Not(
                    car.Model("Mazda"),
                ),
            ).
            All(ctx)
    if err != nil {
        return fmt.Errorf("failed getting cars: %w", err)
    }
    log.Println("cars returned:", cars)
    // Output: (Car(Model=Tesla, RegisteredAt=<Time>), Car(Model=Ford, RegisteredAt=<Time>),)
    return nil
}

```

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

### Create Client and Schema Migration (MySQL)

Source: https://entgo.io/docs/getting-started/index

Opens a connection to a MySQL database and runs the auto-migration tool to create the schema. Replace placeholder connection details with your actual database credentials.

```go
package main

import (
    "context"
    "log"

    "entdemo/ent"

    _ "github.com/go-sql-driver/mysql"
)

func main() {
    client, err := ent.Open("mysql", "<user>:<pass>@tcp(<host>:<port>)/<database>?parseTime=True")
    if err != nil {
        log.Fatalf("failed opening connection to mysql: %v", err)
    }
    defer client.Close()
    // Run the auto migration tool.
    if err := client.Schema.Create(context.Background()); err != nil {
        log.Fatalf("failed creating schema resources: %v", err)
    }
}
```

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

### Create Client and Schema Migration (PostgreSQL)

Source: https://entgo.io/docs/getting-started/index

Opens a connection to a PostgreSQL database and runs the auto-migration tool to create the schema. Ensure you replace placeholder connection details with your actual database credentials.

```go
package main

import (
    "context"
    "log"

    "entdemo/ent"

    _ "github.com/lib/pq"
)

func main() {
    client, err := ent.Open("postgres","host=<host> port=<port> user=<user> dbname=<database> password=<pass>")
    if err != nil {
        log.Fatalf("failed opening connection to postgres: %v", err)
    }
    defer client.Close()
    // Run the auto migration tool.
    if err := client.Schema.Create(context.Background()); err != nil {
        log.Fatalf("failed creating schema resources: %v", err)
    }
}
```

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

### Initialize Go Module

Source: https://entgo.io/docs/getting-started/index

Initializes a new Go module project. This command is essential for managing dependencies and ensuring proper project structure, especially when working outside the GOPATH.

```bash
go mod init entdemo
```

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

### Create Schema Resources with Automatic Migrations (Go)

Source: https://entgo.io/docs/getting-started/index

This Go code snippet demonstrates how to use the `client.Schema.Create` API to automatically create database schema resources based on defined schema objects. It's primarily for prototyping and development, and includes basic error handling for the creation process. Dependencies include the Ent client and a logger.

```go
if err := client.Schema.Create(ctx); err != nil {
    log.Fatalf("failed creating schema resources: %v", err)
}
```

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

### Create User Entity

Source: https://entgo.io/docs/getting-started/index

Creates a new 'User' entity with specified age and name, then saves it to the database. It logs the created user and returns it or an error.

```go
func CreateUser(ctx context.Context, client *ent.Client) (*ent.User, error) {
    u, err := client.User.
        Create().
        SetAge(30).
        SetName("a8m").
        Save(ctx)
    if err != nil {
        return nil, fmt.Errorf("failed creating user: %w", err)
    }
    log.Println("user was created: ", u)
    return u, nil
}
```

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

### Generate Database Migrations with Atlas CLI

Source: https://entgo.io/docs/getting-started/index

These commands use the Atlas CLI to generate migration files. They specify the migration directory, the target schema definition, and a development database URL. The commands are shown for different database systems: MySQL, MariaDB, PostgreSQL, and SQLite. The output is a set of SQL migration files.

```bash
atlas migrate diff migration_name \
  --dir "file://ent/migrate/migrations" \
  --to "ent://ent/schema" \
  --dev-url "docker://mysql/8/ent"
```

```bash
atlas migrate diff migration_name \
  --dir "file://ent/migrate/migrations" \
  --to "ent://ent/schema" \
  --dev-url "docker://mariadb/latest/test"
```

```bash
atlas migrate diff migration_name \
  --dir "file://ent/migrate/migrations" \
  --to "ent://ent/schema" \
  --dev-url "docker://postgres/15/test?search_path=public"
```

```bash
atlas migrate diff migration_name \
  --dir "file://ent/migrate/migrations" \
  --to "ent://ent/schema" \
  --dev-url "sqlite://file?mode=memory&_fk=1"
```

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

### Create Graph Data using Ent Client

Source: https://entgo.io/docs/getting-started/index

This Go function demonstrates how to create nodes (Users, Cars, Groups) and establish relationships between them using the Ent client. It covers creating users, then cars associated with those users, and finally groups with associated users.

```go
func CreateGraph(ctx context.Context, client *ent.Client) error {
    // First, create the users.
    a8m, err := client.User.
        Create().
        SetAge(30).
        SetName("Ariel").
        Save(ctx)
    if err != nil {
        return err
    }
    neta, err := client.User.
        Create().
        SetAge(28).
        SetName("Neta").
        Save(ctx)
    if err != nil {
        return err
    }
    // Then, create the cars, and attach them to the users created above.
    err = client.Car.
        Create().
        SetModel("Tesla").
        SetRegisteredAt(time.Now()).
        // Attach this car to Ariel.
        SetOwner(a8m).
        Exec(ctx)
    if err != nil {
        return err
    }
    err = client.Car.
        Create().
        SetModel("Mazda").
        SetRegisteredAt(time.Now()).
        // Attach this car to Ariel.
        SetOwner(a8m).
        Exec(ctx)
    if err != nil {
        return err
    }
    err = client.Car.
        Create().
        SetModel("Ford").
        SetRegisteredAt(time.Now()).
        // Attach this car to Neta.
        SetOwner(neta).
        Exec(ctx)
    if err != nil {
        return err
    }
    // Create the groups, and add their users in the creation.
    err = client.Group.
        Create().
        SetName("GitLab").
        AddUsers(neta, a8m).
        Exec(ctx)
    if err != nil {
        return err
    }
    err = client.Group.
        Create().
        SetName("GitHub").
        AddUsers(a8m).
        Exec(ctx)
    if err != nil {
        return err
    }
    log.Println("The graph was created successfully")
    return nil
}

```

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

### Apply Migrations with Docker

Source: https://entgo.io/docs/getting-started/index

This command runs the Atlas migration apply command within a Docker container. It mounts the local 'migrations' directory and connects to a MySQL database using the provided URL, applying pending migrations.

```bash
docker run --rm --net=host \
  -v $(pwd)/migrations:/migrations \
  arigaio/atlas migrate apply \
  --url "mysql://root:pass@:3306/test"

```

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

### Create New Ent Schema

Source: https://entgo.io/docs/getting-started/index

Generates the basic schema file for a new entity, in this case 'User'. This command must be run from the project's root directory.

```bash
go run -mod=mod entgo.io/ent/cmd/ent new User
```

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

### Query User by Name using Ent

Source: https://entgo.io/docs/getting-started/index

Demonstrates how to query a single user by their name using the Ent client. It uses the `Only` method, which will return an error if zero or more than one user is found matching the criteria. This function requires a context and an Ent client instance.

```go
func QueryUser(ctx context.Context, client *ent.Client) (*ent.User, error) {
    u, err := client.User.
        Query().
        Where(user.Name("a8m")),
        // `Only` fails if no user found,
        // or more than 1 user returned.
        Only(ctx)
    if err != nil {
        return nil, fmt.Errorf("failed querying user: %w", err)
    }
    log.Println("user returned: ", u)
    return u, nil
}
```

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

### Create and Associate Cars with a User in Ent

Source: https://entgo.io/docs/getting-started/index

Demonstrates creating two 'Car' entities and then creating a 'User' entity, associating the previously created cars with this user using the `AddCars` method. This function saves the entities to the database using the Ent client. It requires a context and an Ent client.

```go
func CreateCars(ctx context.Context, client *ent.Client) (*ent.User, error) {
    // Create a new car with model "Tesla".
    tesla, err := client.Car.
        Create().
        SetModel("Tesla").
        SetRegisteredAt(time.Now()).
        Save(ctx)
    if err != nil {
        return nil, fmt.Errorf("failed creating car: %w", err)
    }
    log.Println("car was created: ", tesla)

    // Create a new car with model "Ford".
    ford, err := client.Car.
        Create().
        SetModel("Ford").
        SetRegisteredAt(time.Now()).
        Save(ctx)
    if err != nil {
        return nil, fmt.Errorf("failed creating car: %w", err)
    }
    log.Println("car was created: ", ford)

    // Create a new user, and add it the 2 cars.
    a8m, err := client.User.
        Create().
        SetAge(30).
        SetName("a8m").
        AddCars(tesla, ford).
        Save(ctx)
    if err != nil {
        return nil, fmt.Errorf("failed creating user: %w", err)
    }
    log.Println("user was created: ", a8m)
    return a8m, nil
}

```

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

### Generate Ent Schemas using CLI

Source: https://entgo.io/docs/getting-started/index

This command uses the Ent CLI to generate initial Go packages for the 'Car' and 'Group' entities. This is a common first step when defining new entities in an Ent project.

```bash
go run -mod=mod entgo.io/ent/cmd/ent new Car Group

```

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

### Query Groups with Associated Users (Ent Go)

Source: https://entgo.io/docs/getting-started/index

This Go function demonstrates how to query for all groups that have at least one user associated with them. It uses a look-aside predicate 'HasUsers()' to filter the groups, showcasing efficient querying for entities with existing relationships.

```go
func QueryGroupWithUsers(ctx context.Context, client *ent.Client) error {
    groups, err := client.Group.
        Query().
        Where(group.HasUsers()).
        All(ctx)
    if err != nil {
        return fmt.Errorf("failed getting groups: %w", err)
    }
    log.Println("groups returned:", groups)
    // Output: (Group(Name=GitHub), Group(Name=GitLab),)
    return nil
}

```

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

### Inspect Ent Schema for SQL Output

Source: https://entgo.io/docs/getting-started/index

This Atlas CLI command inspects the Ent schema at './ent/schema' and formats the output as SQL DDL statements. It uses an in-memory SQLite database for the inspection process.

```bash
atlas schema inspect \
  -u "ent://ent/schema" \
  --dev-url "sqlite://file?mode=memory&_fk=1" \
  --format '{{ sql . "  " }}'

```

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

### Generate Ent Code

Source: https://entgo.io/docs/getting-started/index

Triggers the code generation process for Ent based on the defined schemas. This command should be executed from the project's root directory.

```bash
go generate ./ent
```

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

### Define User Schema Fields

Source: https://entgo.io/docs/getting-started/index

Defines the 'age' (integer, positive) and 'name' (string, default 'unknown') fields for the User entity within its schema file.

```go
package schema

import "entgo.io/ent"

// User holds the schema definition for the User entity.
type User struct {
    ent.Schema
}

// Fields of the User.
func (User) Fields() []ent.Field {
    return []ent.Field{
        field.Int("age").
            Positive(),
        field.String("name").
            Default("unknown"),
    }
}

// Edges of the User.
func (User) Edges() []ent.Edge {
    return nil
}
```

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

### Generate Ent Assets

Source: https://entgo.io/docs/getting-started/index

This command regenerates the Ent client, models, and other generated assets based on the defined schemas. It's typically run after making changes to the schema files.

```bash
go generate ./ent

```

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

### Query Cars Associated with a User in Ent

Source: https://entgo.io/docs/getting-started/index

Shows how to query all cars associated with a given user and how to filter those cars by a specific model ('Ford'). It uses the `QueryCars` method on the user entity and applies filtering with `Where` and `Only` for specific results. This requires a context and a user entity.

```go
func QueryCars(ctx context.Context, a8m *ent.User) error {
    cars, err := a8m.QueryCars().All(ctx)
    if err != nil {
        return fmt.Errorf("failed querying user cars: %w", err)
    }
    log.Println("returned cars:", cars)

    // What about filtering specific cars.
    ford, err := a8m.QueryCars().
        Where(car.Model("Ford")),
        Only(ctx)
    if err != nil {
        return fmt.Errorf("failed querying user cars: %w", err)
    }
    log.Println(ford)
    return nil
}

```

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

### Inspect Ent Schema for ERD Visualization

Source: https://entgo.io/docs/getting-started/index

This Atlas CLI command inspects the Ent schema located at './ent/schema'. It uses an in-memory SQLite database for inspection and generates output suitable for visualizing the schema, likely as an ERD.

```bash
atlas schema inspect \
  -u "ent://ent/schema" \
  --dev-url "sqlite://file?mode=memory&_fk=1" \
  -w

```

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

### Define Edges for Cars and Groups in User Schema (Go)

Source: https://entgo.io/docs/getting-started/index

This Go code snippet defines two edges in the User schema: 'cars' (an edge.To relationship to the Car schema) and 'groups' (an inverse edge.From relationship to the Group schema, referencing the 'users' edge). This sets up a many-to-many relationship between Users and Groups.

```go
// Edges of the User.
func (User) Edges() []ent.Edge {
   return []ent.Edge{
       edge.To("cars", Car.Type),
       // Create an inverse-edge called "groups" of type `Group`
       // and reference it to the "users" edge (in Group schema)
       // explicitly using the `Ref` method.
       edge.From("groups", Group.Type).
           Ref("users"),
   }
}

```

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

### Define Many-to-Many Edge in Group Schema (Go)

Source: https://entgo.io/docs/getting-started/index

This Go code snippet defines an 'edge.To' relationship named 'users' in the Group schema, indicating that a Group can have many associated Users. This is part of setting up a many-to-many relationship.

```go
// Edges of the Group.
func (Group) Edges() []ent.Edge {
   return []ent.Edge{
       edge.To("users", User.Type),
   }
}

```

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

### Define User to Car Edge in Ent Schema

Source: https://entgo.io/docs/getting-started/index

Defines a one-to-many edge named 'cars' from the 'User' entity to the 'Car' entity in Ent. This establishes a relationship where a user can have multiple cars, but each car has a single owner. This is done within the User schema definition.

```go
// Edges of the User.
func (User) Edges() []ent.Edge {
    return []ent.Edge{
        edge.To("cars", Car.Type),
    }
}

```

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

### Define Inverse Edge for Car Owner in Go

Source: https://entgo.io/docs/getting-started/index

This Go code snippet defines an inverse edge named 'owner' in the Car schema, referencing the 'cars' edge in the User schema. It uses the `edge.From` function and the `Ref` method to establish the back-reference, ensuring a car can have only one owner by calling `Unique()`.

```go
// Edges of the Car.
func (Car) Edges() []ent.Edge {
    return []ent.Edge{
        // Create an inverse-edge called "owner" of type `User`
        // and reference it to the "cars" edge (in User schema)
        // explicitly using the `Ref` method.
        edge.From("owner", User.Type).
            Ref("cars").
            // setting the edge to unique, ensure
            // that a car can have only one owner.
            Unique(),
    }
}

```

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

### Define Car Entity Fields in Ent

Source: https://entgo.io/docs/getting-started/index

Defines the fields for the 'Car' entity schema in Ent. It includes a string field for 'model' and a time field for 'registered_at'. This Go code is part of the Ent schema definition process.

```go
// Fields of the Car.
func (Car) Fields() []ent.Field {
    return []ent.Field{
        field.String("model"),
        field.Time("registered_at"),
    }
}

```

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

### Define Group Entity Fields with Validation in Ent

Source: https://entgo.io/docs/getting-started/index

Defines the fields for the 'Group' entity schema in Ent, including a 'name' field with a regular expression validation. The validation ensures the group name only contains letters and underscores. This is part of the Ent schema definition.

```go
// Fields of the Group.
func (Group) Fields() []ent.Field {
    return []ent.Field{
        field.String("name").
            // Regexp validation for group name.
            Match(regexp.MustCompile("[a-zA-Z_]+$")),
    }
}

```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.