gorm associations + CRUD

gorm-example.go

package main

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

type Product struct {
	gorm.Model
	// gorm.Model adds ID, CreatedAt, UpdatedAt, DeletedAt
	Code       string
	Price      uint
	CategoryID int
	Category   Category
}

type Category struct {
	gorm.Model
	Name string
}

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

	// Migrate the schema
	db.AutoMigrate(&Product{}, &Category{})
	seed(db)

	var product Product
	// must .Preload("Category") to get Category property to load
	// https://gorm.io/docs/preload.html
	// db.First(&product, 1) // find product with id of 1
	db.Preload("Category").First(&product, "Code = ?", "D42") // find product with integer primary key

	db.Model(&product).Update("Price", 200)                      // Update single column
	db.Model(&product).Updates(Product{Price: 200, Code: "F42"}) // non-zero fields
	db.Model(&product).Updates(map[string]interface{}{"Price": 200, "Code": "F42"})

	var workout Category
	db.First(&workout, "Name = ?", "Workout")
	db.Model(&product).Update("Category", &workout) // Update the category of product

	// db.Delete(&product, 1) // delete product where id is 1
	db.Where("Code = ?", "F42").Delete(&Product{})
}

func seed(db *gorm.DB) {
	var category Category
	result := db.First(&category, "Name = ?", "Tech")
	if result.RowsAffected == 0 {
		category := &Category{Name: "Tech"}
		db.Create(category)
	}

	var workout Category
	result = db.First(&workout, "Name = ?", "Workout")
	if result.RowsAffected == 0 {
		workout := &Category{Name: "Workout"}
		db.Create(workout)
	}

	var product Product
	result = db.First(&product, "Code = ?", "D42")
	if result.RowsAffected == 0 {
		product := &Product{Code: "D42", Category: category, Price: 100}
		db.Create(&product)
	}
}