[10.x] Allow for converting a HasMany to HasOne && MorphMany to MorphOne

[cosmastech]

Problem

There are often times where I am building a HasMany relationship and I need to get just one item from the collection. This means I have to either define the relationship two times (one for HasMany and then one for HasOne->ofMany()).

class User extends Model
{
    public function logins(): HasMany {
        return $this->hasMany(Login::class, 'some_id', 'the_other_id');
    }
    public function latestLogin(): HasOne {
        return $this->hasOne(Login::class, 'some_id', 'the_other_id')->latestOfMany();
    }
}

As you can imagine, if the design of the DB changes (like during early development of a project) or if the relationship isn't simple, this can be cumbersome or lead to duplication of work.

Proposed Solution

What is added in this PR is the ability to convert a HasMany relationship to HasOne (and MorphMany to MorphOne). So the above code can become

class User extends Model
{
    public function logins(): HasMany {
        return $this->hasMany(Login::class, 'some_id', 'the_other_id');
    }
    public function latestLogin(): HasOne {
        return $this->logins()->hasOne()->latestOfMany();
    }
}

[cosmastech]

If this is something that makes sense, will gladly add HasManyThrough@hasOneThrough() method as well

[taylorotwell]

Thanks

[siarheipashkevich]

@cosmastech could you please check which sql query will be generated? I saw that the sql query has duplicated conditions...

[cosmastech]

@cosmastech could you please check which sql query will be generated? I saw that the sql query has duplicated conditions...

@siarheipashkevich could you provide a code sample the generated SQL?

edit: I see now.

$user->userPreferences()->one()->toSql();
// select * from `user_preferences` where `user_preferences`.`user_id` = ? and `user_preferences`.`user_id` is not null and `user_preferences`.`user_id` = ? and `user_preferences`.`user_id` is not null

[siarheipashkevich]

I've terminal model with next relations:

In Shift model I've opened scope:

Get openedShift from terminal:

Logs:

[2023-03-24 11:41:38] local.INFO: select * from `shifts` where `shifts`.`terminal_id` = ? and `shifts`.`terminal_id` is not null and `shifts`.`terminal_id` = ? and `shifts`.`terminal_id` is not null and `closed_at` is null and `shifts`.`deleted_at` is null limit 1 [480,480] 
[2023-03-24 11:41:38] local.INFO: see logs above  

[siarheipashkevich]

@cosmastech could you please check which sql query will be generated? I saw that the sql query has duplicated conditions...

@siarheipashkevich could you provide a code sample the generated SQL?

edit: I see now.

$user->userPreferences()->one()->toSql();
// select * from `user_preferences` where `user_preferences`.`user_id` = ? and `user_preferences`.`user_id` is not null and `user_preferences`.`user_id` = ? and `user_preferences`.`user_id` is not null

Please take a look at your sql. You also have diplicated conditions

`user_preferences`.`user_id` = ? and `user_preferences`.`user_id` is not null and `user_preferences`.`user_id` = ? and `user_preferences`.`user_id` is not null

[cosmastech]

@siarheipashkevich thank you for reporting this! #46575 should resolve this issue