Gorm查询自定义加入额外列

Question

我正试图从Gorm上的多对多关系中获得额外的列。示例

type Part struct {
Id unit
Name string
}

图

type Diagram struct {
Id unit
Name string
Parts []Part `gorm:"many2many:diagram_parts;"`
}

DiagramPart

type DiagramPart struct{
DiagramId         uint `gorm:"primaryKey"`
PartId            uint `gorm:"primaryKey"`
PartDiagramNumber int
PartNumber        string
PartDescription   string
}

这就是我在Parts中检索PartNumber和PartDescription所做的。

diagram := &Diagram{}
db := s.db.Where("id = ?", 1).
Preload("Parts", func(db *gorm.DB) *gorm.DB {
return db.Select("parts.*, diagram_parts.part_number, diagram_parts.part_description").
Joins("left join diagram_parts on diagram_parts.part_id = parts.id")
}).
First(diagram)

不幸的是，我无法检索part_number, part_description。我该怎么做呢?

Answer 1

可以在structPartOR上添加字段PartNumber和PartDescriptionDiagram，然后在这些字段上添加标签gorm:"-:migration;->"以忽略迁移并进入只读模式。但是根据您的情况，您可以将它添加到structPart中，因为您已经预加载了它。

来源:https://gorm.io/docs/models.html Field-Level-Permission

示例如下:

package main
import (
"fmt"
"gorm.io/driver/sqlite"
"gorm.io/gorm"
)
type Part struct {
Id              uint `gorm:"primaryKey"`
Name            string
PartNumber      string `gorm:"-:migration;->"`
PartDescription string `gorm:"-:migration;->"`
}
type Diagram struct {
Id              uint `gorm:"primaryKey"`
Name            string
Parts           []Part `gorm:"many2many:diagram_parts;"`
// PartNumber      string `gorm:"-:migration;->"`
// PartDescription string `gorm:"-:migration;->"`
}
type DiagramPart struct {
DiagramId         uint `gorm:"primaryKey"`
PartId            uint `gorm:"primaryKey"`
PartDiagramNumber int
PartNumber        string
PartDescription   string
}
func main() {
db, err := gorm.Open(sqlite.Open("test.db"), &gorm.Config{})
if err != nil {
panic("failed to connect database")
}
db.AutoMigrate(&Diagram{}, &Part{}, &DiagramPart{})
diagram := &Diagram{}
err = db.Debug().Where("id = ?", 1).
// Select("diagrams.*, diagram_parts.part_number, diagram_parts.part_description").
Preload("Parts", func(db *gorm.DB) *gorm.DB {
return db.Select("parts.*, diagram_parts.part_number, diagram_parts.part_description").
Joins("left join diagram_parts on diagram_parts.part_id = parts.id")
}).
// Joins("left join diagram_parts on diagram_parts.diagram_id = diagrams.id").
First(diagram).Error
if err != nil {
panic(err)
}
fmt.Printf("diagram: %vn", diagram)
fmt.Println("part number:", diagram.Parts[0].PartNumber)
}