In particular, you can directly use <a href="https://anyio.readthedocs.io/en/stable/" class="external-link" target="_blank">AnyIO</a> for your advanced concurrency use cases that require more advanced patterns in your own code.

        {
            "detail": [
                {
                    "type": "string_pattern_mismatch",
                    "loc": ["body", "q"],
                    "msg": "String should match pattern '^fixedquery$'",
                    "input": "nonregexquery",
                    "ctx": {"pattern": "^fixedquery$"},
                }
            ]
        }
    ) | IsDict(

        {
            "detail": [
                {
                    "type": "string_pattern_mismatch",
                    "loc": ["query", "item-query"],
                    "msg": "String should match pattern '^fixedquery$'",
                    "input": "nonregexquery",
                    "ctx": {"pattern": "^fixedquery$"},
                }
            ]
        }
    ) | IsDict(

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Union[str, None] = Query(
        default=None, min_length=3, max_length=50, pattern="^fixedquery$"
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        str | None, Query(min_length=3, max_length=50, pattern="^fixedquery$")
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

        alias="item-query",
        title="Query string",
        description="Query string for the items to search in the database that have a good match",
        min_length=3,
        max_length=50,
        pattern="^fixedquery$",
        deprecated=True,
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

                        "grant_type": IsDict(
                            {
                                "title": "Grant Type",
                                "anyOf": [
                                    {"pattern": "password", "type": "string"},
                                    {"type": "null"},
                                ],
                            }
                        )
                        | IsDict(

                        "grant_type": IsDict(
                            {
                                "title": "Grant Type",
                                "anyOf": [
                                    {"pattern": "password", "type": "string"},
                                    {"type": "null"},
                                ],
                            }
                        )
                        | IsDict(

```

The response would be like:

```JSON
{
    "X-Token values": [
        "bar",
        "foo"
    ]
}
```

## Recap

Declare headers with `Header`, using the same common pattern as `Query`, `Path` and `Cookie`.

    The **FastAPI** specific code is as small as always.

## ORMs

**FastAPI** works with any database and any style of library to talk to the database.

A common pattern is to use an "ORM": an "object-relational mapping" library.

An ORM has tools to convert ("*map*") between *objects* in code and database tables ("*relations*").