ent 基本使用 三 边（关系处理）

ent 提供了图查询的能力，实际上在关系数据库中的表现就是relation，以下代码接前文

添加边（关系）

  • 添加schema
entc init Car Group

效果：

  • 添加字段
    car
package schema
​
import (
 "github.com/facebookincubator/ent"
 "github.com/facebookincubator/ent/schema/field"
)
​
// Car holds the schema definition for the Car entity.
type Car struct {
 ent.Schema
}
​
// Fields of the Car.
func (Car) Fields() []ent.Field {
 return []ent.Field{
  field.String("model"),
  field.Time("registered_at"),
 }
}
​
// Edges of the Car.
func (Car) Edges() []ent.Edge {
 return nil
}
 

Group

package schema
​
import (
 "regexp"
​
 "github.com/facebookincubator/ent"
 "github.com/facebookincubator/ent/schema/field"
)
​
// Group holds the schema definition for the Group entity.
type Group struct {
 ent.Schema
}
​
// Fields of the Group.
func (Group) Fields() []ent.Field {
 return []ent.Field{
  field.String("name").
   // regexp validation for group name.
   Match(regexp.MustCompile("[a-zA-Z_]+$")),
 }
}
​
// Edges of the Group.
func (Group) Edges() []ent.Edge {
 return nil
}
 
 
  • 定义关系
    以下是一个用户拥有多辆汽车，但是车只能拥有一个所有者


边定义（user schema）

 
package schema
​
import (
 "github.com/facebookincubator/ent"
 "github.com/facebookincubator/ent/schema/edge"
 "github.com/facebookincubator/ent/schema/field"
)
​
// 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.Int("age").
   Positive(),
  field.String("name").
   Default("unknown"),
 }
}
​
// Edges of the User.
func (User) Edges() []ent.Edge {
 return []ent.Edge{
  edge.To("cars", Car.Type),
 }
}
 
 
  • 生成代码
entc generate ./ent/schema
 

效果

  • 创建car 处理

    注意需要运行scheme 迁移 go run cmd/migration/main.go

package main
​
import (
 "context"
 "fmt"
 "log"
 "time"
​
 _ "github.com/go-sql-driver/mysql"
​
 "github.com/rongfengliang/ent-demo/ent"
)
​
func main() {
 client, err := ent.Open("mysql", "root:dalongrong@tcp(127.0.0.1)/gogs")
 if err != nil {
  log.Fatalf("failed opening connection to sqlite: %v", err)
 }
 defer client.Close()
 ctx := context.Background()
 u, err := createCars(ctx, client)
 if err != nil {
  log.Fatal("some wrong", err)
 } else {
  log.Printf("user %s", u)
 }
}
​
func createCars(ctx context.Context, client *ent.Client) (*ent.User, error) {
 // creating new car with model "Tesla".
 tesla, err := client.Car.
  Create().
  SetModel("Tesla").
  SetRegisteredAt(time.Now()).
  Save(ctx)
 if err != nil {
  return nil, fmt.Errorf("failed creating car: %v", err)
 }
​
 // creating new car with model "Ford".
 ford, err := client.Car.
  Create().
  SetModel("Ford").
  SetRegisteredAt(time.Now()).
  Save(ctx)
 if err != nil {
  return nil, fmt.Errorf("failed creating car: %v", err)
 }
 log.Println("car was created: ", ford)
 // create a new user, and add it the 2 cars.
 a8m, err := client.User.
  Create().
  SetAge(30).
  SetName("a8m").
  AddCars(tesla, ford).
  Save(ctx)
 if err != nil {
  return nil, fmt.Errorf("failed creating user: %v", err)
 }
 log.Println("user was created: ", a8m)
 return a8m, nil
}
 
 

运行效果

go run cmd/edge/car/main.go 
2019/10/14 14:26:06 car was created: Car(id=2, model=Ford, registered_at=2019-10-14 14:26:06.869078 +0800 CST m=+0.007888096)
2019/10/14 14:26:06 user was created: User(id=6, age=30, name=a8m)
2019/10/14 14:26:06 user User(id=6, age=30, name=a8m)
  • 生成的ddl
    car
CREATE TABLE `cars` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `model` varchar(255) COLLATE utf8mb4_bin NOT NULL,
  `registered_at` timestamp NULL DEFAULT NULL,
  `user_car_id` bigint(20) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `cars_users_cars` (`user_car_id`),
  CONSTRAINT `cars_users_cars` FOREIGN KEY (`user_car_id`) REFERENCES `users` (`id`) ON DELETE SET NULL
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
 
 

ER 模型

  • 查询car
 
func QueryCars(ctx context.Context, a8m *ent.User) error {
    cars, err := a8m.QueryCars().All(ctx)
    if err != nil {
        return fmt.Errorf("failed querying user cars: %v", err)
    }
    log.Println("returned cars:", cars)
​
    // what about filtering specific cars.
    ford, err := a8m.QueryCars().
        Where(car.ModelEQ("Ford")).
        Only(ctx)
    if err != nil {
        return fmt.Errorf("failed querying user cars: %v", err)
    }
    log.Println(ford)
    return nil
}

添加BackRef

实际上就是上边说的约束，一辆车只能有一个拥有着

  • 给car 对象添加边的约束
 
package schema
​
import (
    "github.com/facebookincubator/ent"
    "github.com/facebookincubator/ent/schema/edge"
    "github.com/facebookincubator/ent/schema/field"
)
​
// Car holds the schema definition for the Car entity.
type Car struct {
    ent.Schema
}
​
// Fields of the Car.
func (Car) Fields() []ent.Field {
    return []ent.Field{
        field.String("model"),
        field.Time("registered_at"),
    }
}
​
// Edges of the Car.
func (Car) Edges() []ent.Edge {
    return []ent.Edge{
        // create an inverse-edge called "owner" of type `User`
        // and reference it to the "cars" edge (in User schema)
        // explicitly using the `Ref` method.
        edge.From("owner", User.Type).
            Ref("cars").
            // setting the edge to unique, ensure
            // that a car can have only one owner.
            Unique(),
    }
}
​
  • 生成代码
entc generate ./ent/schema
  • 运行schema 迁移
go run cmd/migration/main.go

效果
ddl

 
CREATE TABLE `cars` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `model` varchar(255) COLLATE utf8mb4_bin NOT NULL,
  `registered_at` timestamp NULL DEFAULT NULL,
  `user_car_id` bigint(20) DEFAULT NULL,
  `owner_id` bigint(20) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `cars_users_cars` (`user_car_id`),
  CONSTRAINT `cars_users_cars` FOREIGN KEY (`user_car_id`) REFERENCES `users` (`id`) ON DELETE SET NULL
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
 

  • 查询
    cmd/edge/car/main.go
 
package main
​
import (
    "context"
    "fmt"
    "log"
    "time"
​
    _ "github.com/go-sql-driver/mysql"
​
    "github.com/rongfengliang/ent-demo/ent"
)
​
func main() {
    client, err := ent.Open("mysql", "root:dalongrong@tcp(127.0.0.1)/gogs")
    if err != nil {
        log.Fatalf("failed opening connection to sqlite: %v", err)
    }
    defer client.Close()
    ctx := context.Background()
    u, err := createCars(ctx, client)
    if err != nil {
        log.Fatal("some wrong", err)
    } else {
        log.Printf("user %s", u)
    }
    QueryCarUsers(ctx, u)
}
​
func createCars(ctx context.Context, client *ent.Client) (*ent.User, error) {
    // creating new car with model "Tesla".
    tesla, err := client.Car.
        Create().
        SetModel("Tesla").
        SetRegisteredAt(time.Now()).
        Save(ctx)
    if err != nil {
        return nil, fmt.Errorf("failed creating car: %v", err)
    }
​
    // creating new car with model "Ford".
    ford, err := client.Car.
        Create().
        SetModel("Ford").
        SetRegisteredAt(time.Now()).
        Save(ctx)
    if err != nil {
        return nil, fmt.Errorf("failed creating car: %v", err)
    }
    log.Println("car was created: ", ford)
    // create a new user, and add it the 2 cars.
    a8m, err := client.User.
        Create().
        SetAge(30).
        SetName("a8m").
        AddCars(tesla, ford).
        Save(ctx)
    if err != nil {
        return nil, fmt.Errorf("failed creating user: %v", err)
    }
    log.Println("user was created: ", a8m)
    return a8m, nil
}
​
func QueryCarUsers(ctx context.Context, a8m *ent.User) error {
    cars, err := a8m.QueryCars().All(ctx)
    if err != nil {
        return fmt.Errorf("failed querying user cars: %v", err)
    }
    // query the inverse edge.
    for _, ca := range cars {
        owner, err := ca.QueryOwner().Only(ctx)
        if err != nil {
            return fmt.Errorf("failed querying car %q owner: %v", ca.Model, err)
        }
        log.Printf("car %q owner: %q
", ca.Model, owner.Name)
    }
    return nil
}
 
 

效果

go run cmd/edge/car/main.go 
2019/10/14 14:54:08 car was created: Car(id=4, model=Ford, registered_at=2019-10-14 14:54:08.647003 +0800 CST m=+0.007479891)
2019/10/14 14:54:08 user was created: User(id=7, age=30, name=a8m)
2019/10/14 14:54:08 user User(id=7, age=30, name=a8m)
2019/10/14 14:54:08 car "Tesla" owner: "a8m"
2019/10/14 14:54:08 car "Ford" owner: "a8m"
 
 

创建m2m 的关系

需要实现的关系图如下：

  • 添加边的处理
    groups
 
package schema
​
import (
 "regexp"
​
 "github.com/facebookincubator/ent"
 "github.com/facebookincubator/ent/schema/edge"
 "github.com/facebookincubator/ent/schema/field"
)
​
// Group holds the schema definition for the Group entity.
type Group struct {
 ent.Schema
}
​
// Fields of the Group.
func (Group) Fields() []ent.Field {
 return []ent.Field{
  field.String("name").
   // regexp validation for group name.
   Match(regexp.MustCompile("[a-zA-Z_]+$")),
 }
}
​
// Edges of the Group.
func (Group) Edges() []ent.Edge {
 return []ent.Edge{
  edge.To("users", User.Type),
 }
}
 
 

users

package schema
​
import (
 "github.com/facebookincubator/ent"
 "github.com/facebookincubator/ent/schema/edge"
 "github.com/facebookincubator/ent/schema/field"
)
​
// 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.Int("age").
   Positive(),
  field.String("name").
   Default("unknown"),
 }
}
​
// Edges of the User.
func (User) Edges() []ent.Edge {
 return []ent.Edge{
  edge.To("cars", Car.Type),
  edge.From("groups", Group.Type).
   Ref("users"),
 }
}
  • 生成代码
entc generate ./ent/schema
  • 运行模式迁移
go run cmd/migration/main.go
 

生成的er 模型,从图中我们可以看出是通过中间表解决m2m的问题，通过ent/migrate/schema.go 代码可以也看出来

说明

以上是一个简单的关系处理的学习，后边会看看图查询的处理

参考资料

https://entgo.io/docs/getting-started/
https://github.com/rongfengliang/ent-demo

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原文地址：https://www.cnblogs.com/rongfengliang/p/11673455.html