[SOLVED] GORM load associations from existing object

GORM load associations from existing object

I know I can preload associations like this:

type User struct {
  Name string
  Documents []Document
}

type Document struct {
  Name string
}

func loadUser() {
  var u User
  db.Preload("Documents").First(&u) // loads correctly and populates u.Documents
}

But what if I have the user object already loaded and I just want to load the associated objects on it?

func loadUser() {
  var u User
  db.First(&u) // load the plain user object

  if gonnaNeedTheDocs {
    // how can I populate u.Documents (or any other associations) here efficiently?
  }
}

Solution

If you’ve already loaded the User object and only want to load the Documents association when needed, you can use GORM’s Association() method. This avoids reloading the entire user record:

if gonnaNeedTheDocs {
    db.Model(&u).Association("Documents").Find(&u.Documents)
}

This will:

Use the already-loaded u as the base model,
Access the "Documents" association,
And populate u.Documents with the related records.

For more details, see the GORM documentation on Association Mode