E esses modelos estão compartilhando muitos dos dados e duplicando nomes e tipos de atributos.

Nós poderíamos fazer melhor.

Podemos declarar um modelo `UserBase` que serve como base para nossos outros modelos. E então podemos fazer subclasses desse modelo que herdam seus atributos (declarações de tipo, validação, etc.).

Toda conversão de dados, validação, documentação, etc. ainda funcionará normalmente.

{!> ../../docs_src/extra_models/tutorial005.py!}
```

////

## Recap

Use multiple Pydantic models and inherit freely for each case.

labels.fields=Fields
labels.ex_q=Extended Query
labels.ldapProviderUrl=LDAP URL
labels.ldapSecurityPrincipal=User DN
labels.ldapAdminSecurityPrincipal=Bind DN
labels.ldapAdminSecurityCredentials=Password
labels.ldapBaseDn=Base DN
labels.ldapAccountFilter=Account Filter
labels.ldapGroupFilter=Group Filter
labels.ldapMemberofAttribute=memberOf Attribute
labels.oldPassword=Current Password
labels.newPassword=New Password

{!../../docs_src/sql_databases/sql_app/database.py!}
```

### 创建一个`Base`类

现在我们将使用`declarative_base()`返回一个类。

稍后我们将继承这个类，来创建每个数据库模型或类（ORM 模型）：

```Python hl_lines="13"
{!../../docs_src/sql_databases/sql_app/database.py!}
```

## 创建数据库模型

现在让我们看看文件`sql_app/models.py`。

### 用`Base`类来创建 SQLAlchemy 模型

我们将使用我们之前创建的`Base`类来创建 SQLAlchemy 模型。

/// tip

	switch strings.ToUpper(alg) {
	case "CRC32":
		return ChecksumCRC32
	case "CRC32C":
		return ChecksumCRC32C
	case "SHA1":
		return ChecksumSHA1
	case "SHA256":
		return ChecksumSHA256
	case "":
		return ChecksumNone
	}
	return ChecksumInvalid
}

// String returns the type as a string.
func (c ChecksumType) String() string {
	switch {
	case c.Is(ChecksumCRC32):
		return "CRC32"

        switch (form.crudMode) {
        case CrudMode.CREATE:
            return OptionalEntity.of(new WebAuthentication()).map(entity -> {
                entity.setCreatedBy(username);
                entity.setCreatedTime(currentTime);
                return entity;
            });
        case CrudMode.EDIT:
            if (form instanceof EditForm) {

build:release_arm64_linux --config=mkl_aarch64_threadpool
build:release_arm64_linux --copt=-flax-vector-conversions
test:release_arm64_linux --flaky_test_attempts=3

build:release_cpu_macos --config=avx_linux

# Base build configs for macOS
build:release_macos_base --action_env  DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer
build:release_macos_base --define=no_nccl_support=true --output_filter=^$

border-radius: 0.5rem;\n  transition: background-color 0.15s ease-in-out, border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out, -webkit-transform 0.15s ease-in-out;\n  transition: transform 0.15s ease-in-out, background-color 0.15s ease-in-out, border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out;\n  transition: transform 0.15s ease-in-out, background-color 0.15s ease-in-out, border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out, -webkit-transform 0.15s ease-in-out;\n}\n\n@media...

</p>

<pre>
switch tag {
default: s3()
case 0, 1, 2, 3: s1()
case 4, 5, 6, 7: s2()
}

switch x := f(); {  // missing switch expression means "true"
case x &lt; 0: return -x
default: return x
}

switch {
case x &lt; y: f1()
case x &lt; z: f2()
case x == 4: f3()
}
</pre>

<p>

            switch (fileType) {
            case 1:
                importSystemProperties(fileName, tempFile);
                break;
            case 2:
                importGsaXml(fileName, tempFile);
                break;
            case 3:
                importBulk(fileName, tempFile);
                break;
            case 4:
                importFessJson(fileName, tempFile);