# Mixin

`Mixin` 允许你创建可重复使用的 `ent.Schema` 的代码。

`ent.Mixin` 接口定义如下：

```go
type Mixin interface {
    Fields() []ent.Field
}
```

## 例子

一个 `Mixin` 的常见用法是，将通用字段与你的模式混合在一起。

```go
// -------------------------------------------------
// Mixin 定义部分

// TimeMixin 需要实现 ent.Mixin 接口。
// 时间字段及其定义。
type TimeMixin struct{}

func (TimeMixin) Fields() []ent.Field {
    return []ent.Field{
        field.Time("created_at").
            Immutable().
            Default(time.Now),
        field.Time("updated_at").
            Default(time.Now).
            UpdateDefault(time.Now),
    }
}

// DetailsMixin 需要实现 ent.Mixin 接口。
// 详情字段及其定义。
type DetailsMixin struct{}

func (DetailsMixin) Fields() []ent.Field {
    return []ent.Field{
        field.Int("age").
            Positive(),
        field.String("name").
            NotEmpty(),
    }
}

// -------------------------------------------------
// Schema 定义部分

// User 混入了 TimeMixin 和 DetailsMixin 字段。
// 因此 User 有 5 个字段： `created_at`, `updated_at`, `age`, `name` and `nickname`.
type User struct {
    ent.Schema
}

func (User) Mixin() []ent.Mixin {
    return []ent.Mixin{
        TimeMixin{},
        DetailsMixin{},
    }
}

func (User) Fields() []ent.Field {
    return []ent.Field{
        field.String("nickname").
            Unique(),
    }
}

// Pet 混入了 DetailsMixin 字段。
// 因此 Pet 有 3 个字段： `age`, `name` and `weight`.
type Pet struct {
    ent.Schema
}

func (Pet) Mixin() []ent.Mixin {
    return []ent.Mixin{
        DetailsMixin{},
    }
}

func (Pet) Fields() []ent.Field {
    return []ent.Field{
        field.Float("weight"),
    }
}
```


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