Gorm Belongs To Relation failed when owner's field name is same to foreignKey

GORM Playground Link

https://github.com/go-gorm/playground/pull/701

Description

There are two struct User and Profile. Before I add UserID field in User, the test is passed. After I add UserID field, the test failed. And the select sql look like

SELECT * FROM `users` WHERE `users`.`user_id` = 1
SELECT * FROM `profiles`

Here is the code I wrote.

package test

import (
    "github.com/glebarez/sqlite" // Pure go SQLite driver, checkout https://github.com/glebarez/sqlite for details
    "github.com/stretchr/testify/require"
    "github.com/stretchr/testify/suite"
    "gorm.io/gorm"
    //"gorm.io/driver/sqlite" // Sqlite driver based on CGO
    "testing"
)

func TestGormTestSuite(t *testing.T) {
    suite.Run(t, new(GormTestSuite))
}

type GormTestSuite struct {
    suite.Suite
    gormDB *gorm.DB
}

func (suite *GormTestSuite) SetupTest() {
    db, err := gorm.Open(sqlite.Open("gorm.db"), &gorm.Config{})
    require.NoError(suite.T(), err)
    suite.gormDB = db

    err = suite.gormDB.Migrator().DropTable(&User{}, &Profile{})
    require.NoError(suite.T(), err)
    err = suite.gormDB.Migrator().AutoMigrate(&User{}, &Profile{})
    require.NoError(suite.T(), err)
}

func (suite *GormTestSuite) Test_Preload() {
    suite.givenUser(User{ID: 1, Name: "user1"})
    suite.givenProfile(Profile{ID: 1, UserID: 1, Description: "profile1"})

    var p Profile
    err := suite.gormDB.Debug().Preload("User").Find(&p).Error
    require.NoError(suite.T(), err)
    require.Equal(suite.T(), "user1", p.User.Name)
}

func (suite *GormTestSuite) givenProfile(profile Profile) {
    err := suite.gormDB.Create(&profile).Error
    require.NoError(suite.T(), err)
}

func (suite *GormTestSuite) givenUser(user User) {
    err := suite.gormDB.Create(&user).Error
    require.NoError(suite.T(), err)
}

type User struct {
    ID     int
    Name   string
    UserID int
}

type Profile struct {
    ID          int
    UserID      int
    User        User `gorm:"foreignKey:UserID"`
    Description string
}

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Comment From: PoundXI

I had the same issue and spent quite some time debugging, thinking I used the wrong relation type (BelongsTo vs HasOne). Turns out, GORM fails to preload correctly when both child and parent structs have a field with the same name as the foreign key (e.g. UserID), resulting in a null relation.

A temporary workaround is to rename the foreign key fields in both structs to something else, and explicitly map the column name using the gorm:"column:..." tag to keep the actual DB column name unchanged.

Here’s an example:

type User struct {
    ID          int
    Name        string
    UserUserID  int `gorm:"column:user_id;"`
}

type Profile struct {
    ID             int
    ProfileUserID  int  `gorm:"column:user_id;"`
    User           User `gorm:"foreignKey:ProfileUserID"`
    Description    string
}

This works, but adds complexity - particularly when using struct embedding (e.g. a base struct for audit fields) and wanting to reuse common field names like UserID, CreatedBy, or UpdatedBy.

Would be great if GORM could handle this edge case more gracefully.

Comment From: xinnjie

I am experiencing this bug as well. When the foreign key field name in the ownee matches the reference key field in the owner, and the PostgreSQL driver is used, the foreign key constraint is added to the owner table instead of the ownee table.