ent orm筆記3---schema使用(下)

Indexes 索引

在前兩篇的文章中，其實對於索引也有一些使用， 這裏來詳細看一下關於索引的使用

Indexes方法能夠在一個或者多個字段上設置索引，以提升數據檢索的速度或者定義數據的惟一性

在下面這個例子中，對user表的field1 和field2 字段設置了聯合索引;對first_name和last_name設置了聯合惟一索引; 對field3 設置了惟一索引。

這裏須要注意對於單獨的字段設置惟一索引，在Fields中定義字段的時候經過Unique方法便可

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

在創建表關係的時候也能夠對相應的字段設置索引，主要實在特定關係下設置字段的惟一性

在這個例子中，咱們有一個有許多街道的城市，咱們但願在每一個城市下設置街道名稱是惟一的。

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(),
   }
}

在上一篇文章中這種用法咱們已經見過，咱們看一下這樣建立的表信息，主要是看streets這個表：

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 添加索引的信息後，再次查看streets表的信息，其實這裏咱們就是經過添加約束，使得一個城市中每一個街道的名稱是惟一的

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

能夠使用Table選項爲類型提供自定義表名，以下所示:

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容許您建立可重用的ent.Schema代碼。ent.Mixin 接口以下：

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的一個常見用例是將一些經常使用的通用字段進行內置，以下：

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{},
    }
}

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

Builtin Mixin

Mixin提供了一些內置的Mixin，可用於將create_time和update_time字段添加到schema中。

爲了使用它們，將 mixin.Time mixin 添加到schema，以下所示:

package schema

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

type Pet struct {
    ent.Schema
}

func (Pet) Mixin() []ent.Mixin {
    return []ent.Mixin{
        mixin.Time{},
        // Or, mixin.CreateTime only for create_time
        // and mixin.UpdateTime only for update_time.
    }
}

延伸閱讀

• https://entgo.io/