无法创建与gorm的外键关系，其中字段名！=类型名称

Question

我试图在我的应用程序中字段（和db列）的名称不相同的情况下创建“所属”关系作为类型名称。格姆正在抱怨这一点。下面是一个说明问题的一个简单的例子：

package main 

import (
    "fmt" 
    "github.com/jinzhu/gorm" 
    _ "github.com/mattn/go-sqlite3" 
) 

type Car struct { 
    gorm.Model 
    Owner User 
    OwnerID int 
} 

type User struct { 
    gorm.Model 
} 

func main() { 
    db, _ := gorm.Open("sqlite3", "test.db") 
    defer db.Close() 
    db.LogMode(true) 

    db.CreateTable(&Car{}, &User{}) 

    u := User{} 
    u.ID = 1 
    db.Create(&u) 

    c := Car{} 
    c.ID = 1 
    c.Owner = u 
    db.Create(&c) 

    cars := make([]Car, 5) 
    db.Find(&cars) 
    for i := range cars { 
     db.Model(cars[i]).Related(&cars[i].Owner) 
    } 

    for i := range cars { 
     fmt.Println(cars[i].Owner.ID) 
    } 
} 

我们希望这个程序打印出“1”作为自己的最后一行，因为这是用户关系的主键“拥有”唯一的汽车在数据库中。相反，“0”被打印出来，并详细日志记录显示错误在Related(&cars[i].Owner)步：

(/home/nate/gocode/src/foo/main.go:26) 
[2016-04-09 19:33:46] [122.35ms] CREATE TABLE "cars" ("id" integer primary key autoincrement,"created_at" datetime,"updated_at" datetime,"deleted_at" datetime,"owner_id" integer) 

(/home/nate/gocode/src/foo/main.go:26) 
[2016-04-09 19:33:46] [98.96ms] CREATE INDEX idx_cars_deleted_at ON "cars"(deleted_at) 

(/home/nate/gocode/src/foo/main.go:26) 
[2016-04-09 19:33:46] [108.95ms] CREATE TABLE "users" ("id" integer primary key autoincrement,"created_at" datetime,"updated_at" datetime,"deleted_at" datetime) 

(/home/nate/gocode/src/foo/main.go:26) 
[2016-04-09 19:33:46] [125.74ms] CREATE INDEX idx_users_deleted_at ON "users"(deleted_at) 

(/home/nate/gocode/src/foo/main.go:30) 
[2016-04-09 19:33:46] [0.53ms] INSERT INTO "users" ("id","created_at","updated_at","deleted_at") VALUES ('1','2016-04-09T19:33:46-04:00','2016-04-09T19:33:46-04:00','<nil>') 

(/home/nate/gocode/src/foo/main.go:35) 
[2016-04-09 19:33:46] [1.98ms] UPDATE "users" SET "created_at" = '2016-04-09T19:33:46-04:00', "updated_at" = '2016-04-09T19:33:46-04:00', "deleted_at" = '<nil>' WHERE "users".deleted_at IS NULL AND "users"."id" = '1' 

(/home/nate/gocode/src/foo/main.go:35) 
[2016-04-09 19:33:46] [0.43ms] INSERT INTO "cars" ("id","created_at","updated_at","deleted_at","owner_id") VALUES ('1','2016-04-09T19:33:46-04:00','2016-04-09T19:33:46-04:00','<nil>','1') 

(/home/nate/gocode/src/foo/main.go:38) 
[2016-04-09 19:33:46] [0.64ms] SELECT * FROM "cars" WHERE "cars".deleted_at IS NULL 

(/home/nate/gocode/src/foo/main.go:40) 
[2016-04-09 19:33:46] invalid association [] 
0 

这到底是怎么回事？是否在Owner字段中使用了一些特殊标签？我试过使用gorm:"ForeignKey:owner_id"和gorm:"AssociationForeignKey:owner_id"，两者都给出了相同的结果。

Answer 1

在你的情况最简单的方法是指定外国的字段名称。所以，你的

db.Model(cars[i]).Related(&cars[i].Owner) 

应该像

db.Model(cars[i]).Related(&cars[i].Owner, "Owner") 

两种方式是

• 重命名Owner和OwnerID领域User和UserID或
• 重命名User结构Owner

在这些情况下，GORM会自动选择正确的外键。从GORM documentation about associations：

如果字段名称与变量的类型名称相同，则可以省略。