### Example Database Connection URLs

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/config

Examples of connection strings for SQLite, PostgreSQL, and MySQL/MariaDB.

```text
# SQLite, relative to Flask instance path
sqlite:///project.db
```

```text
# PostgreSQL
postgresql://scott:tiger@localhost/project
```

```text
# MySQL / MariaDB
mysql://scott:tiger@localhost/project
```

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

### Install Flask-SQLAlchemy

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/quickstart

Install or update Flask-SQLAlchemy to the latest version using pip.

```bash
$ pip install -U Flask-SQLAlchemy

```

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

### Flask CRUD Operations with SQLAlchemy

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/quickstart

Provides examples for listing, creating, detailing, and deleting users. Remember to call `db.session.commit()` after modifications.

```python
from flask import Flask, request, redirect, url_for, render_template
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///project.db"
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String, unique=True, nullable=False)
    email = db.Column(db.String, unique=True, nullable=False)

    def __repr__(self):
        return f'<User {self.username}>'

@app.route("/users")
def user_list():
    users = db.session.execute(db.select(User).order_by(User.username)).scalars()
    return render_template("user/list.html", users=users)

@app.route("/users/create", methods=["GET", "POST"])
def user_create():
    if request.method == "POST":
        user = User(
            username=request.form["username"],
            email=request.form["email"],
        )
        db.session.add(user)
        db.session.commit()
        return redirect(url_for("user_detail", id=user.id))

    return render_template("user/create.html")

@app.route("/user/<int:id>")
def user_detail(id):
    user = db.get_or_404(User, id)
    return render_template("user/detail.html", user=user)

@app.route("/user/<int:id>/delete", methods=["GET", "POST"])
def user_delete(id):
    user = db.get_or_404(User, id)

    if request.method == "POST":
        db.session.delete(user)
        db.session.commit()
        return redirect(url_for("user_list"))

    return render_template("user/delete.html", user=user)

```

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

### Runtime Error Example

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/contexts

Illustrates the error encountered when attempting database operations outside an active application context.

```text
RuntimeError: Working outside of application context.

This typically means that you attempted to use functionality that needed
the current application. To solve this, set up an application context
with app.app_context(). See the documentation for more information.

```

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

### Example Pagination Iteration

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/pagination

The `iter_pages()` method on the `Pagination` object yields page numbers, potentially separated by `None` to indicate ellipses. This example shows the output for 20 pages with the current page being 7.

```python
users.iter_pages()
[1, 2, None, 5, 6, 7, 8, 9, 10, 11, None, 19, 20]
```

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

### get_engine

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Get the engine for the given bind key for the current application. Requires a Flask application context.

```APIDOC
## get_engine

Get the engine for the given bind key for the current application. This requires that a Flask application context is active. 

Parameters:
    
  * **bind_key** (_str_ _|__None_) – The name of the engine.
  * **kwargs** (_Any_)


Return type:
    
_Engine_
Deprecated since version 3.0: Will be removed in Flask-SQLAlchemy 3.2. Use `engines[key]` instead.
Changelog
Changed in version 3.0: Renamed the `bind` parameter to `bind_key`. Removed the `app` parameter.
```

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

### Assign Reflected Table to Model (Specific Bind)

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/models

This example demonstrates assigning a reflected table to a model when using a specific bind key (e.g., 'auth'). Access the metadata for the specific bind key via `db.metadatas`.

```python
# From an "auth" bind key
class User(db.Model):
    __table__ = db.metadatas["auth"].tables["user"]


```

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

### Define Base Class for Models

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/models

Create a base class for your models by subclassing `DeclarativeBase`. This is the starting point for defining your ORM models.

```python
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy.orm import DeclarativeBase

class Base(DeclarativeBase):
  pass

```

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

### Assign Reflected Table to Model (Default Bind)

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/models

After reflection, you can assign a detected table object to a model's `__table__` attribute. This example shows assignment from the default bind key.

```python
# From the default bind key
class Book(db.Model):
    __table__ = db.metadata.tables["book"]


```

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

### Get or Raise 404 with Custom Message

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/queries

You can provide a custom description to the 404 error raised by `one_or_404` when no matching record is found.

```python
user = db.one_or_404(
    db.select(User).filter_by(username=username),
    description=f"No user named '{username}'."
)

```

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

### Get or Raise 404 for User by ID

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/queries

Use `db.get_or_404()` to retrieve a model instance by its ID, raising a 404 error if not found. This is useful in view functions.

```python
@app.route("/user-by-id/<int:id>")
def user_by_id(id):
    user = db.get_or_404(User, id)
    return render_template("show_user.html", user=user)

```

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

### Get or Raise 404 for User by Username

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/queries

Use `db.one_or_404()` with a select statement to retrieve a single result, raising a 404 error if zero or more than one result is found. This is useful in view functions.

```python
@app.route("/user-by-username/<username>")
def user_by_username(username):
    user = db.one_or_404(db.select(User).filter_by(username=username))
    return render_template("show_user.html", user=user)

```

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

### SQLAlchemy Class

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Integrates SQLAlchemy with Flask, handling engine setup, table/model association, and connection cleanup. It allows access to SQLAlchemy modules and provides a base for defining models.

```APIDOC
## class flask_sqlalchemy.SQLAlchemy(_app =None_, _*_, _metadata =None_, _session_options =None_, _query_class =Query_, _model_class =Model_, _engine_options =None_, _add_models_to_shell =True_, _disable_autonaming =False_)

### Description
Integrates SQLAlchemy with Flask. This handles setting up one or more engines, associating tables and models with specific engines, and cleaning up connections and sessions after each request.

### Parameters:
#### Parameters:
- **app** (_Flask_ _|__None_) – Call `init_app()` on this Flask application now.
- **metadata** (_sa.MetaData_ _|__None_) – Use this as the default `sqlalchemy.schema.MetaData`. Useful for setting a naming convention.
- **session_options** (_dict_ _[__str_ _,__t.Any_ _]__|__None_) – Arguments used by `session` to create each session instance. A `scopefunc` key will be passed to the scoped session, not the session instance. See `sqlalchemy.orm.sessionmaker` for a list of arguments.
- **query_class** (_type_ _[__Query_ _]_) – Use this as the default query class for models and dynamic relationships. The query interface is considered legacy in SQLAlchemy.
- **model_class** (__FSA_MCT_) – Use this as the model base class when creating the declarative model class `Model`. Can also be a fully created declarative model class for further customization.
- **engine_options** (_dict_ _[__str_ _,__t.Any_ _]__|__None_) – Default arguments used when creating every engine. These are lower precedence than application config. See `sqlalchemy.create_engine()` for a list of arguments.
- **add_models_to_shell** (_bool_) – Add the `db` instance and all model classes to `flask shell`.
- **disable_autonaming** (_bool_) – Disable autonaming for table names.
```

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

### Paginate Query Results

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/pagination

Call `db.paginate()` on a select statement to get a `Pagination` object. This method takes `page` and `per_page` arguments from the query string `request.args` during a request. Use `max_per_page` to limit the number of results per page.

```python
page = db.paginate(db.select(User).order_by(User.join_date))
return render_template("user/list.html", page=page)
```

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

### Manual Context for Table Creation

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/contexts

Demonstrates how to manually push an application context to create database tables using `db.create_all()`.

```python
def create_app():
    app = Flask(__name__)
    app.config.from_object("project.config")

    import project.models

    with app.app_context():
        db.create_all()

    return app

```

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

### init_app

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Initialize a Flask application for use with this extension instance. Must be called before accessing database engine or session.

```APIDOC
## init_app

Initialize a Flask application for use with this extension instance. This must be called before accessing the database engine or session with the app.
This sets default configuration values, then configures the extension on the application and creates the engines for each bind key. Therefore, this must be called after the application has been configured. Changes to application config after this call will not be reflected.
The following keys from `app.config` are used:
  * `SQLALCHEMY_DATABASE_URI`
  * `SQLALCHEMY_ENGINE_OPTIONS`
  * `SQLALCHEMY_ECHO`
  * `SQLALCHEMY_BINDS`
  * `SQLALCHEMY_RECORD_QUERIES`
  * `SQLALCHEMY_TRACK_MODIFICATIONS`

Parameters:
    
**app** (_Flask_) – The Flask application to initialize. 

Return type:
    
None
```

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

### Initialize SQLAlchemy Extension

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/models

Create the `db` object by instantiating `SQLAlchemy`, passing your custom base class to the `model_class` argument.

```python
db = SQLAlchemy(model_class=Base)

```

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

### Create All Tables in Database

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/models

After defining your models, use `db.create_all()` within the application context to create the corresponding tables in the database. Ensure all model submodules are imported beforehand.

```python
with app.app_context():
    db.create_all()

```

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

### Configure Multiple Database Binds

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/binds

Set the default database URI and define additional binds using a dictionary mapping bind keys to URLs or configuration dictionaries. Engine options can be specified for each bind.

```python
SQLALCHEMY_DATABASE_URI = "postgresql:///main"
SQLALCHEMY_BINDS = {
    "meta": "sqlite:////path/to/meta.db",
    "auth": {
        "url": "mysql://localhost/users",
        "pool_recycle": 3600,
    },
}

```

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

### create_all

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Creates database tables that do not exist. This method iterates through specified bind keys and calls `metadata.create_all()` for each, but it does not update existing tables.

```APIDOC
## create_all

### Description
Create tables that do not exist in the database by calling `metadata.create_all()` for all or some bind keys. This does not update existing tables, use a migration library for that.
This requires that a Flask application context is active.

### Parameters

#### Path Parameters
* **bind_key** (str | None | list[str | None]) - Optional - A bind key or list of keys to create the tables for. Defaults to all binds.

### Return type
None
```

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

### flask_sqlalchemy.track_modifications.models_committed

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

A Blinker signal emitted after the session is committed if there were changed models. The receiver gets a 'changes' argument with a list of (instance, operation) tuples.

```APIDOC
## models_committed

### Description
This Blinker signal is sent after the session is committed if there were changed models in the session. The sender is the application that emitted the changes. The receiver is passed the `changes` argument with a list of tuples in the form `(instance, operation)`. The operations are `"insert"`, `"update"`, and `"delete"`.
```

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

### Basic Database Connection URL Format

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/config

Use this format for defining your database connection string. Username, password, host, and port are optional based on the database type.

```text
dialect://username:password@host:port/database
```

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

### Configure Flask-SQLAlchemy

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/quickstart

Initialize the SQLAlchemy extension with your Flask app. Ensure SQLALCHEMY_DATABASE_URI is set in your app's configuration.

```python
from flask import Flask
from flask_sqlalchemy import SQLAlchemy

# create the app
app = Flask(__name__)
# configure the SQLite database, relative to the app instance folder
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///project.db"
# initialize the app with the extension
db = SQLAlchemy()
db.init_app(app)

```

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

### Create and Drop Tables for Specific Binds

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/binds

Control table creation and dropping operations for specific binds using the `bind_key` argument in `create_all()` and `drop_all()`. These methods require an application context.

```python
# create tables for all binds
db.create_all()

# create tables for the default and "auth" binds
db.create_all(bind_key=[None, "auth"])

# create tables for the "meta" bind
db.create_all(bind_key="meta")

# drop tables for the default bind
db.drop_all(bind_key=None)

```

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

### Render Simple Pagination Widget

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/pagination

This Jinja macro demonstrates how to create a simple pagination widget using attributes like `first`, `last`, `total`, and `iter_pages()` from the `Pagination` object.

```html
{% macro render_pagination(pagination, endpoint) %}
  <div class="page-items">
    {{ pagination.first }} - {{ pagination.last }} of {{ pagination.total }}
  </div>
  <div class=pagination>
    {% for page in pagination.iter_pages() %}
      {% if page %}
        {% if page != pagination.page %}
          <a href="{{ url_for(endpoint, page=page) }}">{{ page }}</a>
        {% else %}
          <strong>{{ page }}</strong>
        {% endif %}
      {% else %}
        <span class=ellipsis>…</span>
      {% endif %}
    {% endfor %}
  </div>
{% endmacro %}
```

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

### Manual Context for Model Testing

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/contexts

Shows how to push an application context within a test to interact with the database session for model operations.

```python
def test_user_model(app):
    user = User()

    with app.app_context():
        db.session.add(user)
        db.session.commit()

```

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

### get_or_404

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Like session.get() but aborts with a 404 Not Found error instead of returning None.

```APIDOC
## get_or_404

Like `session.get()` but aborts with a `404 Not Found` error instead of returning `None`.
```

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

### first_or_404

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Retrieves the first object in the query result. If no object is found, it aborts with a 404 Not Found error.

```APIDOC
## first_or_404

### Description
Retrieves the first object in the query result. If no object is found, it aborts with a 404 Not Found error instead of returning None.

### Method
Not applicable (this is a method of a Python class).

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Parameters
* **description** (_str_ or _None_) – A custom message to show on the error page.

### Return type
_Any_
```

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

### get_or_404

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Retrieves an object by its primary key. If the object is not found, it aborts with a 404 Not Found error.

```APIDOC
## get_or_404

### Description
Retrieves an object by its primary key. If the object is not found, it aborts with a 404 Not Found error instead of returning None.

### Method
Not applicable (this is a method of a Python class).

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Parameters
* **ident** (_Any_) – The primary key to query.
* **description** (_str_ or _None_) – A custom message to show on the error page.

### Return type
_Any_
```

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

### engines

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Map of bind keys to Engine instances for the current application. The None key refers to the default engine.

```APIDOC
## engines

Map of bind keys to `sqlalchemy.engine.Engine` instances for current application. The `None` key refers to the default engine, and is available as `engine`.
To customize, set the `SQLALCHEMY_BINDS` config, and set defaults by passing the `engine_options` parameter to the extension.
This requires that a Flask application context is active.
Changelog
Added in version 3.0.
```

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

### reflect

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Loads table definitions from the database by calling `metadata.reflect()` for specified bind keys. This operation requires an active Flask application context.

```APIDOC
## reflect

### Description
Load table definitions from the database by calling `metadata.reflect()` for all or some bind keys.
This requires that a Flask application context is active.

### Parameters

#### Path Parameters
* **bind_key** (str | None | list[str | None]) - Optional - A bind key or list of keys to reflect the tables from. Defaults to all binds.

### Return type
None
```

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

### Define SQLAlchemy Models

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/quickstart

Define your database models by subclassing db.Model. Use Mapped and mapped_column for type hints and column definitions.

```python
from sqlalchemy import Integer, String
from sqlalchemy.orm import Mapped, mapped_column

class User(db.Model):
    id: Mapped[int] = mapped_column(primary_key=True)
    username: Mapped[str] = mapped_column(unique=True)
    email: Mapped[str]

```

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

### metadatas

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Map of bind keys to MetaData instances. The None key refers to the default metadata, available as metadata.

```APIDOC
## metadatas

Map of bind keys to `sqlalchemy.schema.MetaData` instances. The `None` key refers to the default metadata, and is available as `metadata`.
Customize the default metadata by passing the `metadata` parameter to the extension. This can be used to set a naming convention. When metadata for another bind key is created, it copies the default’s naming convention.
Changelog
Added in version 3.0.
```

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

### Define Table with a Specific Bind Key

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/binds

Associate a table with a specific database bind by passing the `bind_key` keyword argument during its definition.

```python
user_table = db.Table(
    "user",
    db.Column("id", db.Integer, primary_key=True),
    bind_key="auth",
)

```

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

### Define Model with a Specific Bind Key

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/binds

Associate a model with a specific database bind by setting the `__bind_key__` class attribute. If not set, the default bind is used.

```python
class User(db.Model):
    __bind_key__ = "auth"
    id = db.Column(db.Integer, primary_key=True)

```

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

### engine

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

The default Engine for the current application, used by session if the Model or Table being queried does not set a bind key.

```APIDOC
## engine

The default `Engine` for the current application, used by `session` if the `Model` or `Table` being queried does not set a bind key.
To customize, set the `SQLALCHEMY_ENGINE_OPTIONS` config, and set defaults by passing the `engine_options` parameter to the extension.
This requires that a Flask application context is active.
```

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

### one_or_404

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Retrieves exactly one object from the query result. If no object or multiple objects are found, it aborts with a 404 Not Found error.

```APIDOC
## one_or_404

### Description
Retrieves exactly one object from the query result. If no object or multiple objects are found, it aborts with a 404 Not Found error instead of raising `NoResultFound` or `MultipleResultsFound`.

### Method
Not applicable (this is a method of a Python class).

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Parameters
* **description** (_str_ or _None_) – A custom message to show on the error page.

### Return type
_Any_
```

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

### first_or_404

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Retrieves a single result from a statement or aborts with a 404 error if no result is found. It's similar to `Result.scalar()` but handles the not-found case by raising an HTTP 404 error.

```APIDOC
## first_or_404

### Description
Like `Result.scalar()`, but aborts with a `404 Not Found` error instead of returning `None`.

### Parameters

#### Path Parameters
* **statement** (Select) - Required - The `select` statement to execute.
* **description** (str | None) - Optional - A custom message to show on the error page.

### Return type
Any
```

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

### Reflect All Tables from Database

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/models

Call `db.reflect()` within the application context to detect existing tables in the database and create corresponding table objects. This is useful when connecting to a pre-existing database schema.

```python
with app.app_context():
    db.reflect()


```

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

### drop_all

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Drops database tables for specified bind keys by calling `metadata.drop_all()`. This operation requires an active Flask application context.

```APIDOC
## drop_all

### Description
Drop tables by calling `metadata.drop_all()` for all or some bind keys.
This requires that a Flask application context is active.

### Parameters

#### Path Parameters
* **bind_key** (str | None | list[str | None]) - Optional - A bind key or list of keys to drop the tables from. Defaults to all binds.

### Return type
None
```

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

### Pytest Fixture for Application Context

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/contexts

Provides a pytest fixture to manage application context for tests, ensuring it's pushed and yielded for the test duration.

```python
import pytest

@pytest.fixture
def app_ctx(app):
    with app.app_context():
        yield

@pytest.mark.usefixtures("app_ctx")
def test_user_model():
    user = User()
    db.session.add(user)
    db.session.commit()

```

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

### Table

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

A SQLAlchemy Table class that chooses a metadata automatically. The metadata argument is not required and is selected based on the bind_key argument.

```APIDOC
## Table

A `sqlalchemy.schema.Table` class that chooses a metadata automatically.
Unlike the base `Table`, the `metadata` argument is not required. If it is not given, it is selected based on the `bind_key` argument. 

Parameters:
    
  * **bind_key** – Used to select a different metadata.
  * **args** – Arguments passed to the base class. These are typically the table’s name, columns, and constraints.
  * **kwargs** – Arguments passed to the base class.

Changelog
Changed in version 3.0: This is a subclass of SQLAlchemy’s `Table` rather than a function.
```

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

### Custom Naming Convention for Constraints

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/models

Optionally, construct the `SQLAlchemy` object with a custom `MetaData` object to specify a naming convention for constraints. This ensures consistent and predictable constraint names, which is beneficial for migrations.

```python
from sqlalchemy import MetaData

class Base(DeclarativeBase):
    metadata = MetaData(naming_convention={
        "ix": 'ix_%(column_0_label)s',
        "uq": "uq_%(table_name)s_%(column_0_name)s",
        "ck": "ck_%(table_name)s_%(constraint_name)s",
        "fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
        "pk": "pk_%(table_name)s"
    })


```

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

### paginate

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Applies pagination to a select statement, returning a `Pagination` object. It calculates the offset and limit based on the current page and items per page, with options to control error handling and count calculation.

```APIDOC
## paginate

### Description
Apply an offset and limit to a select statment based on the current page and number of items per page, returning a `Pagination` object.
The statement should select a model class, like `select(User)`. This applies `unique()` and `scalars()` modifiers to the result, so compound selects will not return the expected results.

### Parameters

#### Path Parameters
* **select** (Select) - Required - The `select` statement to paginate.
* **page** (int | None) - Optional - The current page, used to calculate the offset. Defaults to the `page` query arg during a request, or 1 otherwise.
* **per_page** (int | None) - Optional - The maximum number of items on a page, used to calculate the offset and limit. Defaults to the `per_page` query arg during a request, or 20 otherwise.
* **max_per_page** (int | None) - Optional - The maximum allowed value for `per_page`, to limit a user-provided value. Use `None` for no limit. Defaults to 100.
* **error_out** (bool) - Optional - Abort with a `404 Not Found` error if no items are returned and `page` is not 1, or if `page` or `per_page` is less than 1, or if either are not ints. Defaults to True.
* **count** (bool) - Optional - Calculate the total number of values by issuing an extra count query. For very complex queries this may be inaccurate or slow, so it can be disabled and set manually if necessary. Defaults to True.

### Return type
Pagination
```

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

### Model

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

The base class for SQLAlchemy declarative models. Users should subclass db.Model, not this directly, unless customizing the default db.Model.

```APIDOC
## Model

### Description
The base class of the `SQLAlchemy.Model` declarative model class.
To define models, subclass `db.Model`, not this. To customize `db.Model`, subclass this and pass it as `model_class` to `SQLAlchemy`. To customize `db.Model` at the metaclass level, pass an already created declarative model class as `model_class`.

### Attributes

* **__bind_key__**
  Use this bind key to select a metadata and engine to associate with this model’s table. Ignored if `metadata` or `__table__` is set. If not given, uses the default key, `None`.

* **__tablename__**
  The name of the table in the database. This is required by SQLAlchemy; however, Flask-SQLAlchemy will set it automatically if a model has a primary key defined. If the `__table__` or `__tablename__` is set explicitly, that will be used instead.

* **query_class**
  Query class used by `query`. Defaults to `SQLAlchemy.Query`, which defaults to `Query`.
  alias of `Query`

* **query**
  A SQLAlchemy query for a model. Equivalent to `db.session.query(Model)`. Can be customized per-model by overriding `query_class`.
  Warning
  The query interface is considered legacy in SQLAlchemy. Prefer using `session.execute(select())` instead.
```

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

### Model

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

A SQLAlchemy declarative model class. Subclass this to define database models. Table name is generated from class name if not set.

```APIDOC
## Model

A SQLAlchemy declarative model class. Subclass this to define database models.
If a model does not set `__tablename__`, it will be generated by converting the class name from `CamelCase` to `snake_case`. It will not be generated if the model looks like it uses single-table inheritance.
If a model or parent class sets `__bind_key__`, it will use that metadata and database engine. Otherwise, it will use the default `metadata` and `engine`. This is ignored if the model sets `metadata` or `__table__`.
For code using the SQLAlchemy 1.x API, customize this model by subclassing `Model` and passing the `model_class` parameter to the extension. A fully created declarative model class can be passed as well, to use a custom metaclass.
For code using the SQLAlchemy 2.x API, customize this model by subclassing `sqlalchemy.orm.DeclarativeBase` or `sqlalchemy.orm.DeclarativeBaseNoMeta` and passing the `model_class` parameter to the extension.
```

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

### one_or_404

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Retrieves a single, unique result from a statement or aborts with a 404 error. This method is useful when you expect exactly one result and want to handle cases where zero or multiple results are found gracefully.

```APIDOC
## one_or_404

### Description
Like `Result.scalar_one()`, but aborts with a `404 Not Found` error instead of raising `NoResultFound` or `MultipleResultsFound`.

### Parameters

#### Path Parameters
* **statement** (Select) - Required - The `select` statement to execute.
* **description** (str | None) - Optional - A custom message to show on the error page.

### Return type
Any
```

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

### Session-Specific Query Class Customization

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/customizing

Customize only `session.query` by passing the `query_cls` key to the `session_options` argument in the SQLAlchemy constructor.

```python
db = SQLAlchemy(session_options={"query_cls": GetOrQuery})
```

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

### Define a Many-to-Many Association Table

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/models

Create instances of `db.Table` to define tables directly, often used for many-to-many relationships. The `metadata` argument is not required as it's inferred from the `bind_key` or default.

```python
import sqlalchemy as sa

user_book_m2m = db.Table(
    "user_book",
    sa.Column("user_id", sa.ForeignKey(User.id), primary_key=True),
    sa.Column("book_id", sa.ForeignKey(Book.id), primary_key=True),
)


```

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

### metadata

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

The default metadata used by Model and Table if no bind key is set.

```APIDOC
## metadata

The default metadata used by `Model` and `Table` if no bind key is set.
```

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

### Abstract Model for Timestamps

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/customizing

Use an abstract model class to add common fields like creation and update timestamps to specific models. Set `__abstract__ = True` to prevent the abstract model from being mapped to a table.

```python
from datetime import datetime, timezone
from sqlalchemy.orm import Mapped, mapped_column

class TimestampModel(db.Model):
    __abstract__ = True
    created: Mapped[datetime] = mapped_column(default=lambda: datetime.now(timezone.utc))
    updated: Mapped[datetime] = mapped_column(default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))

class Author(db.Model):
    id: Mapped[int] = mapped_column(primary_key=True)
    username: Mapped[str] = mapped_column(unique=True)

class Post(TimestampModel):
    id: Mapped[int] = mapped_column(primary_key=True)
    title: Mapped[str]

```

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

### Insert Data with Flask-SQLAlchemy

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/queries

To insert new data, create a model instance, add it to the session, and commit the transaction.

```python
user = User()
db.session.add(user)
db.session.commit()

```

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

### Execute Select Query with Flask-SQLAlchemy

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/queries

Queries are executed using `db.session.execute()` with `select()`. Use `.scalar_one()` for a single result or `.scalars()` for multiple results.

```python
user = db.session.execute(db.select(User).filter_by(username=username)).scalar_one()

users = db.session.execute(db.select(User).order_by(User.username)).scalars()

```

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

### Custom Session Class for Horizontal Sharding

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/customizing

Implement custom session logic, such as horizontal sharding, by defining a new class that inherits from `ShardedSession` and Flask-SQLAlchemy's `Session`. Pass this custom class via `session_options`.

```python
from sqlalchemy.ext.horizontal_shard import ShardedSession
from flask_sqlalchemy.session import Session

class CustomSession(ShardedSession, Session):
    ...

db = SQLAlchemy(session_options={"class_": CustomSession}) 
```

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

### Enable Data Classes with Base Class

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/models

To enable SQLAlchemy's native support for data classes, include `MappedAsDataclass` as an additional parent class when defining your base model class.

```python
from sqlalchemy.orm import DeclarativeBase, MappedAsDataclass

class Base(DeclarativeBase, MappedAsDataclass):
  pass

```

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

### Relationship-Specific Query Class Customization

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/customizing

Customize the query class for a specific dynamic relationship by passing the `query_class` argument to the `db.relationship` function.

```python
db.relationship(User, lazy="dynamic", query_class=GetOrQuery)
```

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

### Iterating through page numbers

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Yields page numbers for a pagination widget, representing skipped pages with None. All parameters are keyword-only.

```python
1, 2, None, 5, 6, 7, 8, 9, 10, 11, None, 19, 20
```

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

### Listen for Model Changes with Blinker

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/track-modifications

Connect a listener function to the `models_committed` Blinker signal to receive a list of model changes after a commit. Ensure `SQLALCHEMY_TRACK_MODIFICATIONS` is enabled in your Flask app configuration.

```python
from flask_sqlalchemy.track_modifications import models_committed

def get_modifications(sender: Flask, changes: list[tuple[t.Any, str]]) -> None:
    ...

models_committed.connect(get_modifications)


```

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

### Mixin Class for Timestamps

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/customizing

Alternatively, use a mixin class to provide shared behavior like timestamps. Inherit from the mixin class and `db.Model` when defining your models.

```python
class TimestampMixin:
    created: Mapped[datetime] = mapped_column(default=lambda: datetime.now(timezone.utc))
    updated: Mapped[datetime] = mapped_column(default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))

class Post(TimestampMixin, db.Model):
    id: Mapped[int] = mapped_column(primary_key=True)
    title: Mapped[str]

```

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

### session

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

A scoped session that creates instances of Session scoped to the current Flask application context. The session will be removed when the application context exits.

```APIDOC
## session

A `sqlalchemy.orm.scoping.scoped_session` that creates instances of `Session` scoped to the current Flask application context. The session will be removed, returning the engine connection to the pool, when the application context exits.
Customize this by passing `session_options` to the extension.
This requires that a Flask application context is active.
Changelog
Changed in version 3.0: The session is scoped to the current app context.
```

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

### paginate

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Paginates the query results, returning a Pagination object. It allows specifying page number, items per page, and error handling for invalid inputs.

```APIDOC
## paginate

### Description
Applies an offset and limit to the query based on the current page and number of items per page, returning a `Pagination` object.

### Method
Not applicable (this is a method of a Python class).

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Parameters
* **page** (_int_ or _None_) – The current page, used to calculate the offset. Defaults to the `page` query arg during a request, or 1 otherwise.
* **per_page** (_int_ or _None_) – The maximum number of items on a page, used to calculate the offset and limit. Defaults to the `per_page` query arg during a request, or 20 otherwise.
* **max_per_page** (_int_ or _None_) – The maximum allowed value for `per_page`, to limit a user-provided value. Use `None` for no limit. Defaults to 100.
* **error_out** (_bool_) – Abort with a `404 Not Found` error if no items are returned and `page` is not 1, or if `page` or `per_page` is less than 1, or if either are not ints.
* **count** (_bool_) – Calculate the total number of values by issuing an extra count query. For very complex queries this may be inaccurate or slow, so it can be disabled and set manually if necessary.

### Return type
_Pagination_
```

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

### Model-Specific Query Class Customization

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/customizing

Customize the query interface for a specific model by setting the `query_class` attribute directly on the model class.

```python
class User(db.Model):
    query_class = GetOrQuery
```

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

### relationship

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Defines a relationship between SQLAlchemy models, applying the extension's `Query` class for dynamic relationships and backrefs. This enhances how relationships are handled within the Flask-SQLAlchemy context.

```APIDOC
## relationship

### Description
A `sqlalchemy.orm.relationship()` that applies this extension’s `Query` class for dynamic relationships and backrefs.

### Parameters

#### Path Parameters
* **args** (Any)
* **kwargs** (Any)

### Return type
RelationshipProperty[Any]
```

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

### flask_sqlalchemy.record_queries.get_recorded_queries()

Source: https://flask-sqlalchemy.readthedocs.io/en/stable/api

Retrieves a list of recorded query information for the current session. Queries are logged if SQLALCHEMY_RECORD_QUERIES is enabled. Each query info object contains statement, parameters, timing, duration, and location.

```APIDOC
## get_recorded_queries()

### Description
Get the list of recorded query information for the current session. Queries are recorded if the config `SQLALCHEMY_RECORD_QUERIES` is enabled.
Each query info object has the following attributes: 

`statement`
    
The string of SQL generated by SQLAlchemy with parameter placeholders. 

`parameters`
    
The parameters sent with the SQL statement. 

`start_time` / `end_time`
    
Timing info about when the query started execution and when the results where returned. Accuracy and value depends on the operating system. 

`duration`
    
The time the query took in seconds. 

`location`
    
A string description of where in your application code the query was executed. This may not be possible to calculate, and the format is not stable.

### Return Type
list[__QueryInfo_]
```