GORM: Select fields from two tables while joining - go

Question

I have products table which has one-to-many relationship with items and brands tables. brands also have one-to-many relationship with items.
I was trying to query products and group them based on product_id and brand_id and it seems to work fine.
The only problem I have right now is that I can't map these fields brandId and BrandName, They always nil. But querying the raw SQL statement it generates the desired result.
Here are my models. Some fields have been omitted for simplicity.
type Brand struct {
ID int `json:"id" gorm:"primaryKey"`
Name string `json:"name" gorm:"index;not null;type:varchar(50);default:null"`
ProductID int `json:"productId"`
Product *Product `json:"product" gorm:"foreignKey:ProductID;"`
}
type Product struct {
ID int `json:"id" gorm:"primaryKey"`
Name string `json:"name" gorm:"index;not null;type:varchar(50);default:null"`
StoreID *int `json:"storeId"`
Store *Store `json:"store" gorm:"foreignKey:StoreID;constraint:OnUpdate:RESTRICT,OnDelete:RESTRICT;"`
BrandID *int `json:"brandId" gorm:"-"` //SEE THIS
BrandName *string `json:"brandName" gorm:"-"` //SEE THIS TOO
Brands []*Brand `json:"brands" gorm:"constraint:OnUpdate:CASCADE,OnDelete:RESTRICT;"`
}
type Item struct {
ID int `json:"id" gorm:"primaryKey"`
Quantity int `json:"quantity" gorm:"type:integer;not null;unsigned;"`
ProductID int `json:"productId"`
Product *Product `json:"product" gorm:"foreignKey:ProductID;not null;constraint:OnUpdate:RESTRICT,OnDelete:CASCADE;"`
BrandID *int `json:"brandId"`
Brand *Brand `json:"brand" gorm:"foreignKey:BrandID;constraint:OnUpdate:RESTRICT,OnDelete:CASCADE;"`
}
var products []*model.Product
var result *gorm.DB
query := DB.Table("products").
Where(&model.Product{StoreID: &StoreID}).
Joins("INNER JOIN items ON items.product_id = products.id").
Joins("LEFT JOIN brands ON brands.id = items.brand_id").
Where("items.quantity > 0").
Group("products.id, brands.id").
Select("products.*,brands.id AS brand_id, brands.name AS brand_name")
if err := query.Find(&products).Error; err != nil {
panic(err)
}
//Here results contains no brand_id nor brand_name
fmt.Printf("result %+v\n", products)
Here is raw SQL generated by gorm. And work as expected outside gorm
SELECT products.*,brands.id AS brand_id, brands.name AS brand_name
FROM "products"
INNER JOIN items ON items.product_id = products.id
LEFT JOIN brands ON brands.id = items.brand_id
WHERE "products"."store_id" = 2 AND items.quantity > 0
GROUP BY products.id, brands.id
First solution that comes in mind is to use -> instead of - gorm tag.
Like this
BrandID : Int #goTag(key: "gorm", value: "->")
BrandName : String #goTag(key: "gorm", value: "->")
The only drawback with this is that it saves these fields on database.
Any alternative?

Answer 1

has_many
type Brand struct {
ID int `json:"id" gorm:"primaryKey"`
Name string `json:"name" gorm:"index;not null;type:varchar(50);default:null"`
ProductID int `json:"productId"`
}
type Product struct {
ID int `json:"id" gorm:"primaryKey"`
Name string `json:"name" gorm:"index;not null;type:varchar(50);default:null"`
StoreID *int `json:"storeId"`
Store *Store `json:"store" gorm:"foreignKey:StoreID;constraint:OnUpdate:RESTRICT,OnDelete:RESTRICT;"`
Brands []*Brand `json:"brands" gorm:"constraint:OnUpdate:CASCADE,OnDelete:RESTRICT;"`
}
you shouold read BrandId and BrandName in model-Brand but model-Product
Product have many Brands, so it have many BrandID/BrandName, why you defiene just a BrandNameor BrandID?