Skip to content
You're not viewing the latest version. Click here to go to latest.

# CRUD

Generic async CRUD operations for SQLAlchemy models with search, pagination, and many-to-many support.

Info

This module has been coded and tested to be compatible with PostgreSQL only.

## Overview

The `crud` module provides `AsyncCrud`, an abstract base class with a full suite of async database operations, and `CrudFactory`, a convenience function to instantiate it for a given model.

## Creating a CRUD class

    from fastapi_toolsets.crud import CrudFactory
    from myapp.models import User

    UserCrud = CrudFactory(model=User)

`CrudFactory` dynamically creates a class named `AsyncUserCrud` with `User` as its model.

## Basic operations

    # Create
    user = await UserCrud.create(session=session, obj=UserCreateSchema(username="alice"))

    # Get one (raises NotFoundError if not found)
    user = await UserCrud.get(session=session, filters=[User.id == user_id])

    # Get first or None
    user = await UserCrud.first(session=session, filters=[User.email == email])

    # Get multiple
    users = await UserCrud.get_multi(session=session, filters=[User.is_active == True])

    # Update
    user = await UserCrud.update(session=session, obj=UserUpdateSchema(username="bob"), filters=[User.id == user_id])

    # Delete
    await UserCrud.delete(session=session, filters=[User.id == user_id])

    # Count / exists
    count = await UserCrud.count(session=session, filters=[User.is_active == True])
    exists = await UserCrud.exists(session=session, filters=[User.email == email])

## Pagination

Added in `v1.1` (only offset_pagination via `paginate` if `<v1.1`)

Two pagination strategies are available. Both return a `PaginatedResponse` but differ in how they navigate through results.

| `offset_paginate` | `cursor_paginate`
--- | --- | ---
Total count | Yes | No
Jump to arbitrary page | Yes | No
Performance on deep pages | Degrades | Constant
Stable under concurrent inserts | No | Yes
Search compatible | Yes | Yes
Use case | Admin panels, numbered pagination | Feeds, APIs, infinite scroll

### Offset pagination

    @router.get(
        "",
        response_model=PaginatedResponse[User],
    )
    async def get_users(
        session: SessionDep,
        items_per_page: int = 50,
        page: int = 1,
    ):
        return await crud.UserCrud.offset_paginate(
            session=session,
            items_per_page=items_per_page,
            page=page,
        )

The `offset_paginate` method returns a `PaginatedResponse` whose `pagination` field is an `OffsetPagination` object:

    {
      "status": "SUCCESS",
      "data": ["..."],
      "pagination": {
        "total_count": 100,
        "page": 1,
        "items_per_page": 20,
        "has_more": true
      }
    }

Deprecated: `paginate`

The `paginate` function is a backward-compatible alias for `offset_paginate`. This function is deprecated and will be removed in v2.0.

### Cursor pagination

    @router.get(
        "",
        response_model=PaginatedResponse[UserRead],
    )
    async def list_users(
        session: SessionDep,
        cursor: str | None = None,
        items_per_page: int = 20,
    ):
        return await UserCrud.cursor_paginate(
            session=session,
            cursor=cursor,
            items_per_page=items_per_page,
        )

The `cursor_paginate` method returns a `PaginatedResponse` whose `pagination` field is a `CursorPagination` object:

    {
      "status": "SUCCESS",
      "data": ["..."],
      "pagination": {
        "next_cursor": "eyJ2YWx1ZSI6ICIzZjQ3YWM2OS0uLi4ifQ==",
        "prev_cursor": null,
        "items_per_page": 20,
        "has_more": true
      }
    }

Pass `next_cursor` as the `cursor` query parameter on the next request to advance to the next page. `prev_cursor` is set on pages 2+ and points back to the first item of the current page. Both are `null` when there is no adjacent page.

#### Choosing a cursor column

The cursor column is set once on `CrudFactory` via the `cursor_column` parameter. It must be monotonically ordered for stable results:

- Auto-increment integer PKs
- UUID v7 PKs
- Timestamps

Warning

Random UUID v4 PKs are not suitable as cursor columns because their ordering is non-deterministic.

Note

`cursor_column` is required. Calling `cursor_paginate` on a CRUD class that has no `cursor_column` configured raises a `ValueError`.

The cursor value is base64-encoded when returned to the client and decoded back to the correct Python type on the next request. The following SQLAlchemy column types are supported:

SQLAlchemy type | Python type
--- | ---
`Integer`, `BigInteger`, `SmallInteger` | `int`
`Uuid` | `uuid.UUID`
`DateTime` | `datetime.datetime`
`Date` | `datetime.date`
`Float`, `Numeric` | `decimal.Decimal`

    # Paginate by the primary key
    PostCrud = CrudFactory(model=Post, cursor_column=Post.id)

    # Paginate by a timestamp column instead
    PostCrud = CrudFactory(model=Post, cursor_column=Post.created_at)

## Search

Two search strategies are available, both compatible with `offset_paginate` and `cursor_paginate`.

| Full-text search | Faceted search
--- | --- | ---
Input | Free-text string | Exact column values
Relationship support | Yes | Yes
Use case | Search bars | Filter dropdowns

You can use both search strategies in the same endpoint!

### Full-text search

Declare `searchable_fields` on the CRUD class. Relationship traversal is supported via tuples:

    PostCrud = CrudFactory(
        model=Post,
        searchable_fields=[
            Post.title,
            Post.content,
            (Post.author, User.username),  # search across relationship
        ],
    )

You can override `searchable_fields` per call with `search_fields`:

    result = await UserCrud.offset_paginate(
        session=session,
        search_fields=[User.country],
    )

This allows searching with both `offset_paginate` and `cursor_paginate`:

    @router.get(
        "",
        response_model=PaginatedResponse[User],
    )
    async def get_users(
        session: SessionDep,
        items_per_page: int = 50,
        page: int = 1,
        search: str | None = None,
    ):
        return await crud.UserCrud.offset_paginate(
            session=session,
            items_per_page=items_per_page,
            page=page,
            search=search,
        )

    @router.get(
        "",
        response_model=PaginatedResponse[User],
    )
    async def get_users(
        session: SessionDep,
        cursor: str | None = None,
        items_per_page: int = 50,
        search: str | None = None,
    ):
        return await crud.UserCrud.cursor_paginate(
            session=session,
            items_per_page=items_per_page,
            cursor=cursor,
            search=search,
        )

### Faceted search

Added in `v1.2`

Declare `facet_fields` on the CRUD class to return distinct column values alongside paginated results. This is useful for populating filter dropdowns or building faceted search UIs.

Facet fields use the same syntax as `searchable_fields` — direct columns or relationship tuples:

    UserCrud = CrudFactory(
        model=User,
        facet_fields=[
            User.status,
            User.country,
            (User.role, Role.name),  # value from a related model
        ],
    )

You can override `facet_fields` per call:

    result = await UserCrud.offset_paginate(
        session=session,
        facet_fields=[User.country],
    )

The distinct values are returned in the `filter_attributes` field of `PaginatedResponse`:

    {
      "status": "SUCCESS",
      "data": ["..."],
      "pagination": { "..." },
      "filter_attributes": {
        "status": ["active", "inactive"],
        "country": ["DE", "FR", "US"],
        "name": ["admin", "editor", "viewer"]
      }
    }

Use `filter_by` to pass the client's chosen filter values directly — no need to build SQLAlchemy conditions by hand. Any unknown key raises `InvalidFacetFilterError`.

The keys in `filter_by` are the same keys the client received in `filter_attributes`.

Keys are normally the terminal `column.key` (e.g. `"name"` for `Role.name`). When two facet fields share the same column key (e.g. `(Build.project, Project.name)` and `(Build.os, Os.name)`), the relationship name is prepended automatically: `"project__name"` and `"os__name"`.

`filter_by` and `filters` can be combined — both are applied with AND logic.

Use `filter_params()` to generate a dict with the facet filter values from the query parameters:

    from typing import Annotated

    from fastapi import Depends

    UserCrud = CrudFactory(
        model=User,
        facet_fields=[User.status, User.country, (User.role, Role.name)],
    )

    @router.get("", response_model_exclude_none=True)
    async def list_users(
        session: SessionDep,
        page: int = 1,
        filter_by: Annotated[dict[str, list[str]], Depends(UserCrud.filter_params())],
    ) -> PaginatedResponse[UserRead]:
        return await UserCrud.offset_paginate(
            session=session,
            page=page,
            filter_by=filter_by,
        )

Both single-value and multi-value query parameters work:

    GET /users?status=active              → filter_by={"status": ["active"]}
    GET /users?status=active&country=FR   → filter_by={"status": ["active"], "country": ["FR"]}
    GET /users?role=admin&role=editor     → filter_by={"role": ["admin", "editor"]}  (IN clause)

## Sorting

Added in `v1.3`

Declare `order_fields` on the CRUD class to expose client-driven column ordering via `order_by` and `order` query parameters.

    UserCrud = CrudFactory(
        model=User,
        order_fields=[
            User.name,
            User.created_at,
        ],
    )

Call `order_params()` to generate a FastAPI dependency that maps the query parameters to an `OrderByClause` expression:

    from typing import Annotated

    from fastapi import Depends
    from fastapi_toolsets.crud import OrderByClause

    @router.get("")
    async def list_users(
        session: SessionDep,
        order_by: Annotated[OrderByClause | None, Depends(UserCrud.order_params())],
    ) -> PaginatedResponse[UserRead]:
        return await UserCrud.offset_paginate(session=session, order_by=order_by)

The dependency adds two query parameters to the endpoint:

Parameter | Type
--- | ---
`order_by` | `str | null`
`order` | `asc` or `desc`

    GET /users?order_by=name&order=asc   → ORDER BY users.name ASC
    GET /users?order_by=name&order=desc  → ORDER BY users.name DESC

An unknown `order_by` value raises `InvalidOrderFieldError` (HTTP 422).

You can also pass `order_fields` directly to `order_params()` to override the class-level defaults without modifying them:

    UserOrderParams = UserCrud.order_params(order_fields=[User.name])

## Relationship loading

Added in `v1.1`

By default, SQLAlchemy relationships are not loaded unless explicitly requested. Instead of using `lazy="selectin"` on model definitions (which is implicit and applies globally), define a `default_load_options` on the CRUD class to control loading strategy explicitly.

Warning

Avoid using `lazy="selectin"` on model relationships. It fires silently on every query, cannot be disabled per-call, and can cause unexpected cascading loads through deep relationship chains. Use `default_load_options` instead.

    from sqlalchemy.orm import selectinload

    ArticleCrud = CrudFactory(
        model=Article,
        default_load_options=[
            selectinload(Article.category),
            selectinload(Article.tags),
        ],
    )

`default_load_options` applies automatically to all read operations (`get`, `first`, `get_multi`, `offset_paginate`, `cursor_paginate`). When `load_options` is passed at call-site, it fully replaces `default_load_options` for that query — giving you precise per-call control:

    # Only loads category, tags are not loaded
    article = await ArticleCrud.get(
        session=session,
        filters=[Article.id == article_id],
        load_options=[selectinload(Article.category)],
    )

    # Loads nothing — useful for write-then-refresh flows or lightweight checks
    articles = await ArticleCrud.get_multi(session=session, load_options=[])

## Many-to-many relationships

Use `m2m_fields` to map schema fields containing lists of IDs to SQLAlchemy relationships. The CRUD class resolves and validates all IDs before persisting:

    PostCrud = CrudFactory(
        model=Post,
        m2m_fields={"tag_ids": Post.tags},
    )

    post = await PostCrud.create(session=session, obj=PostCreateSchema(title="Hello", tag_ids=[1, 2, 3]))

## Upsert

Atomic `INSERT ... ON CONFLICT DO UPDATE` using PostgreSQL:

    await UserCrud.upsert(
        session=session,
        obj=UserCreateSchema(email="alice@example.com", username="alice"),
        index_elements=[User.email],
        set_={"username"},
    )

## Response serialization

Added in `v1.1`

Pass a Pydantic schema class to `create`, `get`, `update`, or `offset_paginate` to serialize the result directly into that schema and wrap it in a `Response[schema]` or `PaginatedResponse[schema]`:

    class UserRead(PydanticBase):
        id: UUID
        username: str

    @router.get(
        "/{uuid}",
        responses=generate_error_responses(NotFoundError),
    )
    async def get_user(session: SessionDep, uuid: UUID) -> Response[UserRead]:
        return await crud.UserCrud.get(
            session=session,
            filters=[User.id == uuid],
            schema=UserRead,
        )

    @router.get("")
    async def list_users(session: SessionDep, page: int = 1) -> PaginatedResponse[UserRead]:
        return await crud.UserCrud.offset_paginate(
            session=session,
            page=page,
            schema=UserRead,
        )

The schema must have `from_attributes=True` (or inherit from `PydanticBase`) so it can be built from SQLAlchemy model instances.

Deprecated: `as_response`

The `as_response=True` parameter is deprecated and will be removed in v2.0. Replace it with `schema=YourSchema`.

:material-api: API Reference