does_not_work.go

package main

import (
	"log"

	"github.com/jinzhu/gorm"
	_ "github.com/mattn/go-sqlite3"
)

type Image struct {
	ID  uint64
	URL string
}

type User struct {
	ID             uint64
	ProfileImageID uint64 `gorm:"column:profile_image"`
	ProfileImage   Image
}

var schema = `
DROP TABLE IF EXISTS users;
DROP TABLE IF EXISTS images;

CREATE TABLE images(
  id BIGINT PRIMARY KEY,
  url TEXT
);

CREATE TABLE users(
  id BIGINT,
  profile_image BIGINT,

  FOREIGN KEY(profile_image) REFERENCES images(id)
);

INSERT INTO images(id, url) VALUES(1, 'http://example.com/image_1.jpg');
INSERT INTO images(id, url) VALUES(2, 'http://example.com/image_2.jpg');

INSERT INTO users(id, profile_image) VALUES(1, 1);
INSERT INTO users(id, profile_image) VALUES(2, 2);
`

func main() {
	db, _ := gorm.Open("sqlite3", "test.db")
	db.LogMode(true)

	if err := db.Exec(schema).Error; err != nil {
		log.Fatal(err)
	}

	var users []User
	if err := db.Table("users").Preload("ProfileImage").Find(&users).Error; err != nil {
		log.Fatal(err)
	}

	log.Printf("Users: %v", users)
}

does_work.go

package main

import (
	"log"

	"github.com/jinzhu/gorm"
	_ "github.com/mattn/go-sqlite3"
)

type Image struct {
	ID  uint64
	URL string
}

type User struct {
	ID             uint64
	ProfileimageID uint64 `gorm:"column:profile_image"`
	Profileimage   Image
}

var schema = `
DROP TABLE IF EXISTS users;
DROP TABLE IF EXISTS images;

CREATE TABLE images(
  id BIGINT PRIMARY KEY,
  url TEXT
);

CREATE TABLE users(
  id BIGINT,
  profile_image BIGINT,

  FOREIGN KEY(profile_image) REFERENCES images(id)
);

INSERT INTO images(id, url) VALUES(1, 'http://example.com/image_1.jpg');
INSERT INTO images(id, url) VALUES(2, 'http://example.com/image_2.jpg');

INSERT INTO users(id, profile_image) VALUES(1, 1);
INSERT INTO users(id, profile_image) VALUES(2, 2);
`

func main() {
	db, _ := gorm.Open("sqlite3", "test_works.db")
	db.LogMode(true)

	if err := db.Exec(schema).Error; err != nil {
		log.Fatal(err)
	}

	var users []User
	if err := db.Table("users").Preload("Profileimage").Find(&users).Error; err != nil {
		log.Fatal(err)
	}

	log.Printf("Users: %v", users)
}

schema.sql

CREATE TABLE images(
  id BIGINT PRIMARY KEY,
  url TEXT
);

CREATE TABLE users(
  id BIGINT,
  profile_image BIGINT,

  FOREIGN KEY(profile_image) REFERENCES images(id)
);