[nemothekid]

Lets say I have a relationship where a User has one Profile.

    type User Struct { Id int ProfileId int Profile Profile }
    type Profile Struct { Id int }

For a load like this:

    var u User
    db.Model(&User{}).Preload("Profile").Where("id = ?", 7).Take(&u)

Gorm will do something like this:

    SELECT * FROM users WHERE id=7;
    SELECT * FROM profiles WHERE id=7;

Where a join would be more desirable (only involves 1 trip to the db):

    SELECT * FROM users JOIN profiles ON profiles.id=users.profileid WHERE users.id=7

This also has a huge effect on when your initial queries aren't restricted by ID. Gorm will do huge "id IN (1,2,3,4)" queries - or sometimes if I need to filter on a relation (i.e. get users where profile.foo = bar), I end up doing the join getting that data anyways, then the eager queries loads that data again.

[bigpigeon]

In "OneToOne" and "BelongTo" Join is match but in "ManyToMany" and "OneToMany" will generate duplicate data

I think add Join method and only support "One Data" preload is good way