description: 当数据库需要频繁更新结构时,代码与数据库难以保持一致是烦人的问题.而golang的gorm库,有Auto Migration功能,可以根据go里的struct tag自动更新数据库结构, 非常方便.
最近在写测试, 很明显每一个单元测试最好就在运行时自动清空数据库. gorm的Auto Migration功能就可以满足此功能.
Auto Migration
Automatically migrate your schema, to keep your schema update to date.
WARNING: AutoMigrate will ONLY create tables, missing columns and missing indexes, and WON'T change existing column's type or delete unused columns to protect your data.
最重要的是, 索引(index), 约束(constrants), 类型(type)还有默认值(default)都可以设置,但是文档并没有详细的介绍,经过我的搜索与测试,终于摸清所有的关系.
AutoMigration只会根据struct tag建立新表, 没有的列以及索引, 不会改变已经存在的列的类型或者删除没有用到的列. 所以需要动态更新的话,还是需要在auto migration前DROP TABLE删除整个表再重建. 如:
func clearDatebase() {
db := GetTestClient().NewConn()
db.Exec("DROP TABLE books")
db.AutoMigrate(&mystructtag.books{})
db.Exec("DROP TABLE book_users")
db.AutoMigrate(&mystructtag.book_users{})
}
gorm:
- primary_key 设置主键
- not null 非空约束
- size:64 类型大小,通常是指varchar
以上主要就是size和not null并没有在文档上出现, 其他都可以从例子找到, 自己意会啦.
type User struct {
gorm.Model
Birthday time.Time
Age int
Name string `gorm:"size:255"` // Default size for string is 255, reset it with this tag
Num int `gorm:"AUTO_INCREMENT"`
CreditCard CreditCard // One-To-One relationship (has one - use CreditCard's UserID as foreign key)
Emails []Email // One-To-Many relationship (has many - use Email's UserID as foreign key)
BillingAddress Address // One-To-One relationship (belongs to - use BillingAddressID as foreign key)
BillingAddressID sql.NullInt64
ShippingAddress Address // One-To-One relationship (belongs to - use ShippingAddressID as foreign key)
ShippingAddressID int
IgnoreMe int `gorm:"-"` // Ignore this field
Languages []Language `gorm:"many2many:user_languages;"` // Many-To-Many relationship, 'user_languages' is join table
}
