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注解

结构注解(Schema annotations) 允许附加元数据到结构对象(例如字段和边) 上面，并且将元数据注入到外部模板中。 注解是一种Go类型，它能进行JSON序列化(例如 struct, map 或 slice)，并且需要实现Annotation接口。

内置注解能够配置不同的存储驱动(例如 SQL)，控制代码生成输出。

自定义表名​

使用 entsql 注解的类型, 可以自定义表名，如下所示：

ent/schema/user.go
package schema

import (
    "entgo.io/ent"
    "entgo.io/ent/dialect/entsql"
    "entgo.io/ent/schema"
    "entgo.io/ent/schema/field"
)

// User类型持有用户实体的结构(schema)定义
type User struct {
    ent.Schema
}

// 用户实体的注解
func (User) Annotations() []schema.Annotation {
    return []schema.Annotation{
        entsql.Annotation{Table: "Users"},
    }
}

// 用户实体的字段
func (User) Fields() []ent.Field {
    return []ent.Field{
        field.Int("age"),
        field.String("name"),
    }
}

Custom Table Schema​

Using the Atlas migration engine, an Ent schema can be defined and managed across multiple database schemas. Check out the multi-schema doc for more information.

Foreign Keys Configuration​

Ent allows to customize the foreign key creation and provide a referential action for the ON DELETE clause:

ent/schema/user.go
package schema

import (
    "entgo.io/ent"
    "entgo.io/ent/dialect/entsql"
    "entgo.io/ent/schema/edge"
    "entgo.io/ent/schema/field"
)

// User类型持有用户实体的结构(schema)定义
type User struct {
    ent.Schema
}

// 用户实体的字段
func (User) Fields() []ent.Field {
    return []ent.Field{
        field.String("name").
            Default("Unknown"),
    }
}

// 用户实体的关系
func (User) Edges() []ent.Edge {
    return []ent.Edge{
        edge.To("posts", Post.Type).
            Annotations(entsql.OnDelete(entsql.Cascade)),
    }
}

The example above configures the foreign key to cascade the deletion of rows in the parent table to the matching rows in the child table.

Database Comments​

By default, table and column comments are not stored in the database. However, this functionality can be enabled by using the WithComments(true) annotation. For example:

ent/schema/user.go
package schema

import (
    "entgo.io/ent"
    "entgo.io/ent/dialect/entsql"
    "entgo.io/ent/schema"
    "entgo.io/ent/schema/field"
)

// User holds the schema definition for the User entity.
type User struct {
    ent.Schema
}

// Annotations of the User.
func (User) Annotations() []schema.Annotation {
    return []schema.Annotation{
        // Adding this annotation to the schema enables
        // comments for the table and all its fields.
        entsql.WithComments(true),
        schema.Comment("Comment that appears in both the schema and the generated code"),
    }
}

// Fields of the User.
func (User) Fields() []ent.Field {
    return []ent.Field{
        field.String("name").
            Comment("The user's name"),
        field.Int("age").
            Comment("The user's age"),
        field.String("skipped").
            Comment("This comment won't be stored in the database").
            // Explicitly disable comments for this field.
            Annotations(
                entsql.WithComments(false),
            ),
    }
}