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ent orm笔记2---schema使用(下)

2020-08-28 01:50 1386 查看

Indexes 索引

在前两篇的文章中，其实对于索引也有一些使用，这里来详细看一下关于索引的使用

Indexes方法可以在一个或者多个字段上设置索引，以提高数据检索的速度或者定义数据的唯一性 2088

在下面这个例子中，对user表的

field1

和

field2

字段设置了联合索引;对

first_name

和

last_name

设置了联合唯一索引; 对

field3

设置了唯一索引。

这里需要注意对于单独的字段设置唯一索引，在Fields中定义字段的时候通过Unique方法即可

package schema

import (
"github.com/facebook/ent"
"github.com/facebook/ent/schema/field"
"github.com/facebook/ent/schema/index"
)

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

// Fields of the User.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("field1"),
field.String("field2"),
field.String("field3").Unique(),
field.String("first_name"),
field.String("last_name"),
}
}

// Edges of the User.
func (User) Edges() []ent.Edge {
return nil
}

func Indexes() []ent.Index {
return []ent.Index{
// non-unique index.
index.Fields("field1", "field2"),
// unique index
index.Fields("first_name", "last_name").Unique(),
}
}

查看一下生成的表的信息：

CREATE TABLE `users` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`field1` varchar(255) COLLATE utf8mb4_bin NOT NULL,
`field2` varchar(255) COLLATE utf8mb4_bin NOT NULL,
`field3` varchar(255) COLLATE utf8mb4_bin NOT NULL,
`first_name` varchar(255) COLLATE utf8mb4_bin NOT NULL,
`last_name` varchar(255) COLLATE utf8mb4_bin NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `field3` (`field3`),
UNIQUE KEY `user_first_name_last_name` (`first_name`,`last_name`),
KEY `user_field1_field2` (`field1`,`field2`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin

Index On Edges

在建立表关系的时候也可以对相应的字段设置索引，主要实在特定关系下设置字段的唯一性

在这个例子中，我们有一个有许多街道的城市，我们希望在每个城市下设置街道名称是唯一的。

ent/schema/city.go

package schema

import (
"github.com/facebook/ent"
"github.com/facebook/ent/schema/edge"
"github.com/facebook/ent/schema/field"
)

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

// Fields of the City.
func (City) Fields() []ent.Field {
return []ent.Field{
field.String("name"),
}
}

// Edges of the City.
func (City) Edges() []ent.Edge {
return []ent.Edge{
edge.To("streets", Street.Type),
}
}

ent/schema/street.go

package schema

import (
"github.com/facebook/ent"
"github.com/facebook/ent/schema/edge"
"github.com/facebook/ent/schema/field"
)

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

// Fields of the Street.
func (Street) Fields() []ent.Field {
return []ent.Field{
field.String("name"),
}
}

// Edges of the Street.
func (Street) Edges() []ent.Edge {
return []ent.Edge{
edge.From("city", City.Type).
Ref("streets").
Unique(),
}
}

在上一篇文章中这种用法我们已经见过，我们看一下这样创建的表信息，主要是看streets这个表：

CREATE TABLE `streets` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`name` varchar(255) COLLATE utf8mb4_bin NOT NULL,
`city_streets` bigint(20) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `streets_cities_streets` (`city_streets`),
CONSTRAINT `streets_cities_streets` FOREIGN KEY (`city_streets`) REFERENCES `cities` (`id`) ON DELETE SET NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin

在

ent/schema/street.go

添加索引的信息后，再次查看streets表的信息，其实这里我们就是通过添加约束，使得一个城市中每个街道的名称是唯一的

func (Street) Indexes() []ent.Index {
return []ent.Index{
index.Fields("name").
Edges("city").
Unique(),
}
}

CREATE TABLE `streets` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`name` varchar(255) COLLATE utf8mb4_bin NOT NULL,
`city_streets` bigint(20) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `street_name_city_streets` (`name`,`city_streets`),
KEY `streets_cities_streets` (`city_streets`),
CONSTRAINT `streets_cities_streets` FOREIGN KEY (`city_streets`) REFERENCES `cities` (`id`) ON DELETE SET NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin

Config

可以使用Table选项为类型提供自定义表名，如下所示:

package schema

import (
"github.com/facebook/ent"
"github.com/facebook/ent/schema/field"
)

type User struct {
ent.Schema
}

func (User) Config() ent.Config {
return ent.Config{
Table: "Users",
}
}

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

Mixin

Mixin允许您创建可重用的

ent.Schema

代码。

ent.Mixin

接口如下：

Mixin interface {
// Fields returns a slice of fields to add to the schema.
Fields() []Field
// Edges returns a slice of edges to add to the schema.
Edges() []Edge
// Indexes returns a slice of indexes to add to the schema.
Indexes() []Index
// Hooks returns a slice of hooks to add to the schema.
// Note that mixin hooks are executed before schema hooks.
Hooks() []Hook
}

Mixin的一个常见用例是将一些常用的通用字段进行内置，如下：

package schema

import (
"time"

"github.com/facebook/ent"
"github.com/facebook/ent/schema/field"
"github.com/facebook/ent/schema/mixin"
)

// -------------------------------------------------
// Mixin definition

// TimeMixin implements the ent.Mixin for sharing
// time fields with package schemas.
type TimeMixin struct{
// We embed the `mixin.Schema` to avoid
// implementing the rest of the methods.
mixin.Schema
}

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 implements the ent.Mixin for sharing
// entity details fields with package schemas.
type DetailsMixin struct{
// We embed the `mixin.Schema` to avoid
// implementing the rest of the methods.
mixin.Schema
}

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

// -------------------------------------------------
// Schema definition

// User schema mixed-in the TimeMixin and DetailsMixin fields and therefore
// has 5 fields: `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 schema mixed-in the DetailsMixin fields and therefore
// has 3 fields: `age`, `name` and `weight`.
type Pet struct {
ent.Schema
}

func (Pet) Mixin() []ent.Mixin {
return []ent.Mixin{
DetailsMixin{},
}
56c

}

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

Builtin Mixin

Mixin

提供了一些内置的

Mixin

，可用于将create_time和update_time字段添加到schema中。

为了使用它们，将

mixin.Time mixin

添加到schema，如下所示: