GORM: two foreign keys to one table

Question

I want to create three tables: Users, Events, Pairs.

In the Pair-table there will be three columns: eventId, user1, user2. So user1, user2 will both reference Users table by id.

I know how to this in sql, but i want to try to use ORM. I've read the docs, but i didn't get how to do that

type User struct {
    Id       uint64 `gorm:"primarykey"`
    TGtag    string
    IsActive bool
}

type RCEvent struct {
    Id          uint64 `gorm:"primarykey"`
    DateStarted time.Time
    IsActive    bool
}

type Pair struct {
    EventId uint64
    UserID1 uint64
    UserID2 uint64
}

I've tried to do something with gorm-tags, something like this, but it didn't hepled:

type User struct {
    Id       uint64 `gorm:"primarykey"`
    TGtag    string
    IsActive bool
}

type RCEvent struct {
    Id          uint64 `gorm:"primarykey"`
    DateStarted time.Time
    IsActive    bool
    Pairs       []Pair `gorm:"many2many:pair;"`
}

type Pair struct {
    EventId uint64 `gorm:"primarykey"`
    UserID1 uint64 `gorm:"primarykey"`
    UserID2 uint64 `gorm:"primarykey"`
}

Also, i tried something like and got runtime errors

type User struct {
    Id       uint64 `gorm:"primarykey"`
    TGtag    string
    IsActive bool
}

type RCEvent struct {
    Id          uint64 `gorm:"primarykey"`
    DateStarted time.Time
    IsActive    bool
}

type Pair struct {
    Event   RCEvent
    User1 User //`gorm:"foreignkey:UserId"`
    User2 User //`gorm:"foreignkey:UserId"`
}

[error] failed to parse value &db.Pair{Event:db.RCEvent{Id:0x0, DateStarted:time.Date(1, time.January, 1, 0, 0, 0, 0, time.UTC), IsActive:false}, User1:db.User{Id:0x0, TGtag:"", IsActive:false}, User2:db.User{Id:0x0, TGtag:"", IsActive:false}}, got error invalid field found for struct untitledPetProject/internal/db.Pair's field Event: define a valid foreign key for relations or implement the Valuer/Scanner interface

Answer 1

to use another struct as foreign key you should add it's id as another field in target struct, for your case here is the working example(using gorm example):

package main

import (
    "log"
    "time"

    "gorm.io/driver/sqlite"
    "gorm.io/gorm"
)

type User struct {
    gorm.Model
    ID       uint64 `gorm:"primarykey"`
    TGtag    string
    IsActive bool
}

type RCEvent struct {
    gorm.Model
    ID          uint64 `gorm:"primarykey"`
    DateStarted time.Time
    IsActive    bool
}

type Pair struct {
    gorm.Model
    ID      uint64 `gorm:"primarykey"`
    EventID uint64
    Event   RCEvent
    User1ID uint64
    User1   User
    User2ID uint64
    User2   User
}

func main() {
    db, err := gorm.Open(sqlite.Open("test.db"), &gorm.Config{})
    if err != nil {
        panic("failed to connect database")
    }

    // Migrate the schema
    err = db.AutoMigrate(&User{})
    if err != nil {
        log.Fatal(err)
    }
    err = db.AutoMigrate(&RCEvent{})
    if err != nil {
        log.Fatal(err)
    }
    err = db.AutoMigrate(&Pair{})
    if err != nil {
        log.Fatal(err)
    }

    // Create
    user1 := User{ID: 2, TGtag: "mohammad"}
    user2 := User{ID: 3, TGtag: "ali"}
    event := RCEvent{ID: 2}
    pair := Pair{ID: 2, EventID: 2, Event: event, User1ID: 2, User1: user1, User2ID: 3, User2: user2}
    db.Create(&user1)
    db.Create(&user2)
    db.Create(&event)
    db.Create(&pair)

    // Read
    var user User
    db.First(&user, 3)                   // find product with integer primary key
    db.First(&user, "t_gtag = ?", "ali") // find product with code D42

    // Update - update product's price to 200
    db.Model(&user).Update("is_active", false)
    // Update - update multiple fields
    db.Model(&user).Updates(User{ID: 4, TGtag: "ahmad"}) // non-zero fields
    db.Model(&user).Updates(map[string]interface{}{"Id": 5, "TGtag": "hasan"})

    // Delete - delete product
    db.Delete(&user, 2)
}