GORM的"有很多"关联没有创建外键？

Question

按照 GORM 文档 (http://gorm.io/docs/has_many.html#Has-Many( 中的一个例子，我尝试创建一个具有一对多关系的User和CreditCard模型：

package main
import (
"github.com/jinzhu/gorm"
_ "github.com/jinzhu/gorm/dialects/sqlite"
"github.com/sirupsen/logrus"
)
type User struct {
gorm.Model
CreditCards []CreditCard
}
type CreditCard struct {
gorm.Model
Number string
UserID uint
}
func main() {
db, err := gorm.Open("sqlite3", "examplegorm.db")
if err != nil {
logrus.Fatalf("open db: %v", err)
}
defer db.Close()
db.LogMode(true)
db.AutoMigrate(&User{})
db.AutoMigrate(&CreditCard{})
}

但是，在生成的记录SQL语句中，我没有看到类似的东西

CREATE TABLE credit_cards(
...
FOREIGN KEY(user_id) REFERENCES users(id)
)

正如我对SQLite的文档(https://www.sqlite.org/foreignkeys.html(所期望的那样。我看到的是

> go run gorm_has_many.go
(/Users/kurt/Documents/Scratch/gorm_has_many.go:28) 
[2020-01-06 09:05:58]  [0.82ms]  CREATE TABLE "users" ("id" integer primary key autoincrement,"created_at" datetime,"updated_at" datetime,"deleted_at" datetime )  
[0 rows affected or returned ] 
(/Users/kurt/Documents/Scratch/gorm_has_many.go:28) 
[2020-01-06 09:05:58]  [0.55ms]  CREATE INDEX idx_users_deleted_at ON "users"(deleted_at)   
[0 rows affected or returned ] 
(/Users/kurt/Documents/Scratch/gorm_has_many.go:29) 
[2020-01-06 09:05:58]  [0.52ms]  CREATE TABLE "credit_cards" ("id" integer primary key autoincrement,"created_at" datetime,"updated_at" datetime,"deleted_at" datetime,"number" varchar(255),"user_id" integer )  
[0 rows affected or returned ] 
(/Users/kurt/Documents/Scratch/gorm_has_many.go:29) 
[2020-01-06 09:05:58]  [0.50ms]  CREATE INDEX idx_credit_cards_deleted_at ON "credit_cards"(deleted_at)   
[0 rows affected or returned ] 

相比之下，在djangoapp应用程序中的示例 Django 项目中，如果我有以下models.py：

from django.db import models

class User(models.Model):
name = models.CharField(max_length=255)
age = models.PositiveIntegerField()

class CreditCard(models.Model):
number = models.CharField(max_length=255)
user = models.ForeignKey('djangoapp.User', on_delete=models.CASCADE)

我检查了与创建CreditCard模型相对应的 SQL 语句，我确实看到了外键引用：

kurt@Kurts-MacBook-Pro-13 ~/D/S/djangoproject> python manage.py sqlmigrate djangoapp 0002_creditcard
(0.000) 
SELECT name, type FROM sqlite_master
WHERE type in ('table', 'view') AND NOT name='sqlite_sequence'
ORDER BY name; args=None
(0.000) SELECT "django_migrations"."id", "django_migrations"."app", "django_migrations"."name", "django_migrations"."applied" FROM "django_migrations"; args=()
(0.000) PRAGMA foreign_keys = OFF; args=None
(0.000) PRAGMA foreign_keys; args=None
(0.000) BEGIN; args=None
CREATE TABLE "djangoapp_creditcard" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "number" varchar(255) NOT NULL, "user_id" integer NOT NULL REFERENCES "djangoapp_user" ("id") DEFERRABLE INITIALLY DEFERRED); (params None)
(0.000) PRAGMA foreign_key_check; args=None
CREATE INDEX "djangoapp_creditcard_user_id_eca64c45" ON "djangoapp_creditcard" ("user_id"); (params ())
(0.000) PRAGMA foreign_keys = ON; args=None
BEGIN;
--
-- Create model CreditCard
--
CREATE TABLE "djangoapp_creditcard" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "number" varchar(255) NOT NULL, "user_id" integer NOT NULL REFERENCES "djangoapp_user" ("id") DEFERRABLE INITIALLY DEFERRED);
CREATE INDEX "djangoapp_creditcard_user_id_eca64c45" ON "djangoapp_creditcard" ("user_id");
COMMIT;

为什么user_id列不像 Django 应用程序中那样使用REFERENCES子句生成？(似乎 GORM 有一个addForeignKey()方法 (https://github.com/jinzhu/gorm/blob/79a77d771dee4e4b60e9c543e8663bbc80466670/scope.go#L1229-L1238(，但在此示例中未调用它(。

更新

由于 GORM 的AddForeignKey()方法似乎实际上并没有在 GORM 本身中调用，因此我添加了以下行：

db.Model(&CreditCard{}).AddForeignKey("user_id", "users(id)", "CASCADE", "CASCADE")

但是，重新运行脚本似乎会显示语法错误：

(/Users/kurt/Documents/Scratch/gorm_has_many.go:30) 
[2020-01-06 09:36:29]  near "CONSTRAINT": syntax error 
(/Users/kurt/Documents/Scratch/gorm_has_many.go:30) 
[2020-01-06 09:36:29]  [0.06ms]  ALTER TABLE "credit_cards" ADD CONSTRAINT credit_cards_user_id_users_id_foreign FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE ON UPDATE CASCADE;  
[0 rows affected or returned ] 

Answer 1

Gorm 在自动迁移时不会添加外键。你必须手动完成。

SQLite 不支持在创建表后添加约束。这就是您遇到错误的原因。检查此资源：如何将外键添加到现有 SQLite 表？