Puedes crear dependencias que tengan **sub-dependencias**.

Pueden ser tan **profundas** como necesites.

**FastAPI** se encargará de resolverlas.

## Primera dependencia "dependable" { #first-dependency-dependable }

Podrías crear una primera dependencia ("dependable") así:

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[8:9] *}

Declara un parámetro de query opcional `q` como un `str`, y luego simplemente lo devuelve.

Elles peuvent être aussi profondes que nécessaire.

**FastAPI** se chargera de les résoudre.

## Créer une première dépendance « dependable » { #first-dependency-dependable }

Vous pouvez créer une première dépendance (« dependable ») comme :

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[8:9] *}

Elle déclare un paramètre de requête optionnel `q` de type `str`, puis le retourne simplement.

Elas podem ter o nível de **profundidade** que você achar necessário.

O **FastAPI** se encarrega de resolver essas dependências.

## Primeira dependência "dependable" { #first-dependency-dependable }

Você pode criar uma primeira dependência ("dependable") dessa forma:

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[8:9] *}

**FastAPI** 负责处理解析不同深度的子依赖项。

## 第一层依赖项 “dependable” { #first-dependency-dependable }

你可以创建一个第一层依赖项（“dependable”），如下：

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[8:9] *}

这段代码声明了类型为 `str` 的可选查询参数 `q`，然后返回这个查询参数。

这个函数很简单（不过也没什么用），但却有助于让我们专注于了解子依赖项的工作方式。

## 第二层依赖项，“dependable”和“dependant” { #second-dependency-dependable-and-dependant }

接下来，创建另一个依赖项函数（一个“dependable”），并同时为它自身再声明一个依赖项（因此它同时也是一个“dependant”）：

		}
	}
}

func testStorageAPIRenameFile(t *testing.T, storage StorageAPI) {
	err := storage.AppendFile(t.Context(), "foo", "myobject", []byte("foo"))
	if err != nil {
		t.Fatalf("unexpected error %v", err)
	}

	err = storage.AppendFile(t.Context(), "foo", "otherobject", []byte("foo"))
	if err != nil {
		t.Fatalf("unexpected error %v", err)
	}

	testCases := []struct {

	// Create test files for further reading.
	for i, appendFile := range appendFiles {
		err = xlStorage.AppendFile(t.Context(), volume, appendFile.fileName, []byte("hello, world"))
		if err != appendFile.expectedErr {
			t.Fatalf("Creating file failed: %d %#v, expected: %s, got: %s", i+1, appendFile, appendFile.expectedErr, err)
		}
	}

	{
		buf := make([]byte, 5)

		t.Fatalf("Creating a volume failed with %s expected to pass.", err)
	}

	// Attempt to create a file to verify the permissions later.
	// AppendFile creates file with 0666 perms.
	if err = disk.AppendFile(t.Context(), testCase.volName, pathJoin("hello-world.txt", xlStorageFormatFile), []byte("Hello World")); err != nil {
		t.Fatalf("Create a file `test` failed with %s expected to pass.", err)
	}

                }
            }
        }

        // Add all LICENSE and NOTICE files in licenses directory
        seen.forEach((name, file) -> {
            appendFile(file, name, "NOTICE", output);
            appendFile(new File(file.getParentFile(), name + "-LICENSE.txt"), name, "LICENSE", output);
        });

        // Find any source files with "@notice" annotated license header

Let's see a very simple example. It will be so simple that it is not very useful, for now.

But this way we can focus on how the **Dependency Injection** system works.

### Create a dependency, or "dependable" { #create-a-dependency-or-dependable }

Let's first focus on the dependency.

It is just a function that can take all the same parameters that a *path operation function* can take:

	defer os.Remove(name2)
	f.WriteString("bbbbbbbbbb")
	f.Close()

	if err = AppendFile(name1, name2, false); err != nil {
		t.Error(err)
	}

	b, err := os.ReadFile(name1)
	if err != nil {
		t.Error(err)
	}

	expected := "aaaaaaaaaabbbbbbbbbb"
	if string(b) != expected {
		t.Errorf("AppendFile() failed, expected: %s, got %s", expected, string(b))
	}
}