Fetching a struct and other data in one query - database

Question

I have the following table schema:
user
-----
id uuid
name string
user_model
------
id uuid
user_id uuid
model_id uuid
role int
model
_____
id uuid
name string
model_no string
I have the following code which fetches the data from the "model" table.
underlyingModel = &model{}
var model IModel
model = underlyingModel
role := 0
db.Table("model").Joins('INNER JOIN user_model ON user.id = user_model.uuid')
.Joins('INNER JOIN model ON user.id = model_id').Find(&model);
In my actual code, the model can be many different struct types with different fields, they're all behind the IModel interface.
What I want to do is to fetch that extra role field from the user_model in one query. Something like .Find(&model, &role).
Is it possible using Gorm?

Answer 1

One possible solution is to create an anonymous struct to put the results in, with a combination of the Select() method.
var selectModel struct {
ID string //I'm assuming uuid matches the string
Name string
ModelNo string
Role int
}
db.Table("model").
Joins("INNER JOIN user_model ON user.id = user_model.uuid").
Joins("INNER JOIN model ON user.id = model_id").
Select("model.id, model.name, model.model_no, user_model.role").
Find(&selectModel);
Basically, you create an anonymous struct with selectModel variable, containing all the fields you want to return. Then, you need to do a select statement because you need some fields that are not part of the model table.
Here you can find more info on Smart Select Fields in form.
EDIT:
Based on additional info from the comments, there is a solution that might work.
Your IModel interface could have two methods in its signature, one to extract a string for the SELECT part of the SQL query, and the other one to get a pointer of the selectModel that you would use in the Find method.
type IModel interface {
SelectFields() string
GetSelectModel() interface{}
}
The implementation would go something like this:
func (m *model) SelectFields() string {
return "model.id, model.name, model.model_no, user_model.role"
}
func (m *model) GetSelectModel() interface{} {
return &m.selectModel
}
type model struct {
selectModel
ID uint64
Age int
}
type selectModel struct {
Name string
Email string
}
Then, your query could look something like this:
var m IModel
m = model{}
db.Table("model").
Joins("INNER JOIN user_model ON user.id = user_model.uuid").
Joins("INNER JOIN model ON user.id = model_id").
Select(m.GetSelectFields()).
Find(m.GetSelectModel());