如何正确调用gorm别名？

Question

Here is my code:

package main

import (
    "fmt"
    "time"

    "github.com/jinzhu/gorm"
    _ "github.com/jinzhu/gorm/dialects/sqlite"
)

type ClientCustomer struct {
    Id       int `json:"Id"`
    Name     string
    Created  time.Time
    key      string
    UserId   int `gorm:"user_id"`
    Modified time.Time
}

func (ClientCustomer) TableName() string {
    return "Client_customer"
}

type ClientCustomerInvitation struct {
    Id               int
    CustomerId       int `gorm:"customer_id"`
    CodeInvitationId int `gorm:"codeinvitation_id"`
}

func (ClientCustomerInvitation) TableName() string {
    return "Client_customer_invitation"
}

func main() {
    db, err := gorm.Open("sqlite3", "db.sqlite3?cache=shared&mode=rwc")
    if err != nil {
        panic("failed to connect database")
    }
    defer db.Close()
    var clientCustomer ClientCustomer
    rows, err := db.Model(&ClientCustomer{}).Rows()
    defer rows.Close()
    if err != nil {
        panic(err)
    }
    var clientCustomerInvitation ClientCustomerInvitation
    for rows.Next() {
        db.ScanRows(rows, &clientCustomer)
        db.First(&clientCustomerInvitation, "customer_id = ?", clientCustomer.Id)
        fmt.Println(clientCustomer)
        fmt.Println(clientCustomerInvitation)

    }

}

but I'm not fond of this line:

db.First(&clientCustomerInvitation, "customer_id = ?", clientCustomer.Id)

Is there a way to call "customer_id" from the struct directly instead of using a string?

Ideally I would like to do something like:

 db.First(&clientCustomerInvitation, ClientCustomerInvitation.CustomerId.gormAlias+" = ?", clientCustomer.Id)

I'm looking for a way to use the gorm alias for mapping the field in way that is more elegant and re usable than a mere string.

Answer 1

The only way to be able to get tag value from certain struct field, is by using reflect.

My suggestion, create a function that return tag value from specific struct field. Something like below:

func getGormAlias(obj interface{}, fieldName string) string {
    if field, ok := reflect.TypeOf(obj).FieldByName(fieldName); ok {
        return field.Tag.Get("gorm")
    }

    return ""
}

Then use it to get the tag value.

gormAliasCustomerId := getGormAlias(ClientCustomerInvitation{}, "CustomerId")
db.First(&clientCustomerInvitation, gormAliasCustomerId + " = ?", clientCustomer.Id)

---

Basically what getGormAlias() function does:

• Use the reflect.Type on obj to get the reflect.Type value.
• Then call .FieldByName() to get the reflect.Value object from selected field name.
• The tag information is available through .Tag property. Use that to get the tag value of gorm.