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Go GORM many2many问题

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我无法找到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"`
}

下面是我用DB播种的数据示例

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，上面在Brewer表中创建了重复的Brewers . 我的问题是，引用已经存在但不在Brewer表中创建另一个Brewer项目的Brewer的最佳方法是什么？..还有什么是将新Brewer添加到Beer集合中的最佳方法？

谢谢，贾斯汀

postgresql go foreign-keys many-to-many go-gorm

3 回答

  • 0

    尝试创造第一啤酒，然后酿造啤酒，并使用.append方法将啤酒酿造商添加到啤酒中 .

    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"})
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  • 0

    不确定您是否认为这是一个选项 - 更好的方法是在Beers.Brewers字段中保留对（一片）Brewer ID的引用 . 在对数据进行编码时，您可以将这些ID转换为完整的字段值（使用自定义的编组功能） . 除非您考虑速度/性能，否则这可能是合适的 .

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  • 2

    所以我想出了一个解决方案，我想在上面做什么 . 要将 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 Beer.Brewers 收集 Beer.Brewers ，然后追加 . 无法预加载导致Append覆盖 Brewers 的所有 Brewers

    回复于

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