GORM preload: How to use a custom table name - sql

Question

I have a GORM query with a preload that works just fine because I'm binding it to a struct called "companies" which is also the name of the corresponding database table:
var companies []Company
db.Preload("Subsidiaries").Joins("LEFT JOIN company_prod ON company_products.company_id = companies.id").Where("company_products.product_id = ?", ID).Find(&companies)
Now I want to do something similar, but bind the result to a struct that does not have a name that refers to the "companies" table:
var companiesFull []CompanyFull
db.Preload("Subsidiaries").Joins("LEFT JOIN company_prod ON company_products.company_id = companies.id").Where("company_products.product_id = ?", ID).Find(&companies)
I've simplified the second call for better understanding, the real call has more JOINs and returns more data, so it can't be bound to the "companies" struct.
I'm getting an error though:
column company_subsidiaries.company_full_id does not exist
The corresponding SQL query:
SELECT * FROM "company_subsidiaries" WHERE "company_subsidiaries"."company_full_id" IN (2,1)
There is no "company_subsidiaries.company_full_id", the correct query should be:
SELECT * FROM "company_subsidiaries" WHERE "company_subsidiaries"."company_id" IN (2,1)
The condition obviously gets generated from the name of the struct the result is being bound to. Is there any way to specify a custom name for this case?
I'm aware of the Tabler interface technique, however it doesn't work for Preload I believe (tried it, it changes the table name of the main query, but not the preload).
Updated: More info about the DB schema and structs
DB schema
TABLE companies
ID Primary key
OTHER FIELDS
TABLE products
ID Primary key
OTHER FIELDS
TABLE subsidiaries
ID Primary key
OTHER FIELDS
TABLE company_products
ID Primary key
Company_id Foreign key (companies.id)
Product_id Foreign key (products.id)
TABLE company_subsidiaries
ID Primary key
Company_id Foreign key (companies.id)
Subsidiary_id Foreign key (subsidiaries.id)
Structs
type Company struct {
Products []*Product `json:"products" gorm:"many2many:company_products;"`
ID int `json:"ID,omitempty"`
}
type CompanyFull struct {
Products []*Product `json:"products" gorm:"many2many:company_products;"`
Subsidiaries []*Subsidiary `json:"subsidiaries" gorm:"many2many:company_products;"`
ID int `json:"ID,omitempty"`
}
type Product struct {
Name string `json:"name"`
ID int `json:"ID,omitempty"`
}
type Subsidiary struct {
Name string `json:"name"`
ID int `json:"ID,omitempty"`
}
Generated SQL (by GORM)
SELECT * FROM "company_subsidiaries" WHERE "company_subsidiaries"."company_full_id" IN (2,1)
SELECT * FROM "subsidiaries" WHERE "subsidiaries"."id" IN (NULL)
SELECT companies.*, company_products.*, FROM "companies" LEFT JOIN company_products ON company_products.company_id = companies.id WHERE company_products.product_id = 1

Answer 1

Seems like the way to go in this case may be to customize the relationship in your CompanyFull model. Using joinForeignKey the following code works.
type CompanyFull struct {
Products []*Product `json:"products" gorm:"many2many:company_products;joinForeignKey:ID"`
Subsidiaries []*Subsidiary `json:"subsidiaries" gorm:"many2many:company_subsidiaries;joinForeignKey:ID"`
ID int `json:"ID,omitempty"`
}
func (CompanyFull) TableName() string {
return "companies"
}
func main(){
...
result := db.Preload("Subsidiaries").Joins("LEFT JOIN company_products ON company_products.company_id = companies.id").Where("company_products.product_id = ?", ID).Find(&companies)
if result.Error != nil {
log.Println(result.Error)
} else {
log.Printf("%#v", companies)
}
For more info regarding customizing the foreign keys used in relationships, take a look at the docs https://gorm.io/docs/many_to_many.html#Override-Foreign-Key