This can be very useful for setting up **resources** that you need to use for the whole app, and that are **shared** among requests, and/or that you need to **clean up** afterwards. For example, a database connection pool, or loading a shared machine learning model.

## Use Case { #use-case }

Let's start with an example **use case** and then see how to solve it with this.

@app.get("/items/")
async def read_items(
    q: Annotated[
        Union[str, None],
        Query(
            title="Query string",
            description="Query string for the items to search in the database that have a good match",
            min_length=3,
        ),
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

async def read_items(
    q: Annotated[
        Union[str, None],
        Query(
            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,
        ),
    ] = None,
):

@app.get("/items/")
async def read_items(
    q: Union[str, None] = Query(
        default=None,
        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:

would be valid to use as a **FastAPI** dependency.

In fact, FastAPI uses those two decorators internally.

///

## A database dependency with `yield` { #a-database-dependency-with-yield }

For example, you could use this to create a database session and close it after finishing.

Only the code prior to and including the `yield` statement is executed before creating a response:

Do you want to just have a `str`? Or just a `dict`? Or a database class model instance directly? It all works the same way.

You actually don't have users that log in to your application but robots, bots, or other systems, that have just an access token? Again, it all works the same.

 */

package jcifs.smb1.dcerpc.msrpc;

/**
 * MSRPC implementation for opening an LSA policy handle.
 * This class provides functionality to open a handle to the LSA policy
 * database on a remote server using the LSA RPC interface.
 */
public class MsrpcLsarOpenPolicy2 extends lsarpc.LsarOpenPolicy2 {

    /**
     * Creates a new request to open an LSA policy handle.
     *

 */
package org.apache.maven.building;

import java.io.IOException;
import java.io.InputStream;

/**
 * Provides access to the contents of a source independently of the backing store (e.g. file system, database, memory).
 *
 * @deprecated since 4.0.0, use {@link org.apache.maven.api.services} instead
 */
@Deprecated(since = "4.0.0")
public interface Source {

    /**

package schema

import (
	"gorm.io/gorm/clause"
)

// ConstraintInterface database constraint interface
type ConstraintInterface interface {
	GetName() string
	Build() (sql string, vars []interface{})
}

// GormDataTypeInterface gorm data type interface
type GormDataTypeInterface interface {
	GormDataType() string
}

// FieldNewValuePool field new scan value pool
type FieldNewValuePool interface {
	Get() interface{}

 */

package jcifs.dcerpc.msrpc;

/**
 * MSRPC implementation for connecting to the SAM service.
 * This class provides functionality to establish a connection to the
 * Security Account Manager (SAM) database using the SAMR RPC interface.
 */
public class MsrpcSamrConnect2 extends samr.SamrConnect2 {

    /**
     * Creates a new request to connect to the SAM service.
     *