我无法找出向模型添加关联的最佳方法。我有以下结构
type Beer struct {
ID uint `json:"id"`
Name string `json:"name" gorm:"not null;" sql:"unique"`
Description string `json:"description" gorm:"not null;"`
ImageURL string `json:"image_url"`
AlcoholContent float64 `json:"alcohol_content, default:0"`
Featured bool `json:"featured"`
BrewStart time.Time `json:"brew_start"`
BrewEnd time.Time `json:"brew_end"`
Brewers []Brewer `gorm:"many2many:beer_brewers" json:"brewers"`
}
type Brewer struct {
ID uint `json:"id"`
FirstName string `json:"first_name"`
LastName string `json:"last_name"`
Title string `json:"title"`
Featured bool `json:"featured"`
Beers []Beer `gorm:"many2many:beer_brewers" json:"beers"`
}
下面是我为数据库设定种子的数据示例
Beer{
Name: "some pale ale",
Description: "a description of some pale ale",
ImageURL: "http://via.placeholder.com/350x150",
AlcoholContent: 4.5,
Featured: false,
BrewStart: utils.ParseTime("30-10-2017 13:00 (AEDT)"),
BrewEnd: utils.ParseTime("14-11-2017 13:00 (AEDT)"),
Brewers: []Brewer{
Brewer{FirstName: "john", LastName: "smith", Title: "bottle shaker", Featured: false},
Brewer{FirstName: "joe", LastName: "bloggs", Title: "bottle maker", Featured: true},
},
},
Beer{
Name: "some lager",
Description: "a description of some pale ale",
ImageURL: "http://via.placeholder.com/350x150",
AlcoholContent: 4.5,
Featured: false,
BrewStart: utils.ParseTime("30-10-2017 13:00 (AEDT)"),
BrewEnd: utils.ParseTime("14-11-2017 13:00 (AEDT)"),
Brewers: []Brewer{
Brewer{FirstName: "john", LastName: "smith", Title: "bottle shaker", Featured: false},
Brewer{FirstName: "joe", LastName: "bloggs", Title: "bottle maker", Featured: true},
},
},
但是,上述内容在布鲁尔表中创建了重复的酿酒商。我的问题是,引用已经存在的 Brewer 但不在 Brewer 表中创建另一个 Brewer 项目的最佳方法是什么?..以及将新酿酒师附加到啤酒系列中的最佳方法是什么?
谢谢Justin
尝试先创建啤酒,然后创建酿酒商,并使用 .append 方法将酿酒商附加到啤酒中。
http://jinzhu.me/gorm/associations.html#association-mode
// Start Association Mode
var user User
db.Model(&user).Association("Languages")
// `user` is the source, it need to be a valid record (contains primary key)
// `Languages` is source's field name for a relationship.
// If those conditions not matched, will return an error, check it with:
// db.Model(&user).Association("Languages").Error
// Query - Find out all related associations
db.Model(&user).Association("Languages").Find(&languages)
// Append - Append new associations for many2many, has_many, will replace current association for has_one, belongs_to
db.Model(&user).Association("Languages").Append([]Language{languageZH, languageEN})
db.Model(&user).Association("Languages").Append(Language{Name: "DE"})
所以我已经找到了我想在上面做的事情的解决方案。要将新Brewer
添加到Beer.Brewers
集合中,我需要执行以下操作,
brewerr := Brewer{}
db.Where(&Brewer{FirstName: "justin"}).Find(&brewerr)
beerr := Beer{}
db.Preload("Brewers").Where(&Beer{Name: "some lager"}).Find(&beerr).Association("Brewers").Append(&brewerr)
重要的是要注意,我需要先Preload
Beer.Brewers
集合,然后再追加。未能预加载导致追加覆盖该Beer
的所有Brewers
的想法如下1. 您独立创建酿酒师2.附加它们时,添加主键字段"BrewerId",如图所示3.这将在酿酒商表中查找酿酒商并将其添加到啤酒中。
import (
"time"
"github.com/jinzhu/gorm"
// used by gorm
_ "github.com/jinzhu/gorm/dialects/postgres"
)
type Beer struct {
BeerId uint `json:"id"`
Name string `json:"name" gorm:"not null;" sql:"unique"`
Description string `json:"description" gorm:"not null;"`
ImageURL string `json:"image_url"`
AlcoholContent float64 `json:"alcohol_content, default:0"`
Featured bool `json:"featured"`
BrewStart time.Time `json:"brew_start"`
BrewEnd time.Time `json:"brew_end"`
Brewers []Brewer `json:"brewers" gorm:"many2many:beer_brewers;association_foreignkey:brewer_id;foreignkey:beer_id"`
}
type Brewer struct {
BrewerId uint `json:"id"`
FirstName string `json:"first_name"`
LastName string `json:"last_name"`
Title string `json:"title"`
Featured bool `json:"featured"`
}
func migrate() {
// Connection is the connection string
connection := "host=%v port=%v user=%v dbname=%v password=%v sslmode=%v connect_timeout=%v"
db, _ := gorm.Open("postgres", connection)
db.AutoMigrate(&Beer{}, &Brewer{})
db.Model(&Beer{}).Related(&Brewer{}, "Brewers")
db.Create(&Brewer{FirstName: "justin"})
db.Create(&Beer{
Name: "some lager",
Description: "a description of some pale ale",
ImageURL: "http://via.placeholder.com/350x150",
AlcoholContent: 4.5,
Featured: false,
BrewStart: utils.ParseTime("30-10-2017 13:00 (AEDT)"),
BrewEnd: utils.ParseTime("14-11-2017 13:00 (AEDT)"),
}).Association("Brewers").Append(&Brewer{BrewerId: 123,})
}
不确定您是否考虑过这是一种选择 - 更好的方法可能是在您的 Beers.Brewers 字段中保留对(一部分)Brewer ID 的引用。在对数据进行编码时,您可以将这些 ID 转换为完整字段值(使用自定义封送函数)。这可能很合适,除非您有速度/性能考虑。