How to Select Specific Columns in Laravel's Eloquent `with()` Function?

Specifying Specific Columns in Eloquent's "With()" Function

When leveraging the "with()" function in Laravel's Eloquent ORM to fetch related data from multiple tables, you may encounter situations where you only require specific columns from the second table. This article delves into how to achieve this without resorting to the Query Builder.

Consider the scenario where you have two tables, "User" and "Post," with a one-to-many relationship between them. In your User model, you define a "hasMany" relationship with the Post model:

public function post()
{
    return $this->hasmany('post');
}

Similarly, in the Post model, you establish a "belongsTo" relationship with the User model:

public function user()
{
    return $this->belongsTo('user');
}

However, when you use the "with()" function to join these two tables, you may notice that it selects all columns from the second table by default. Suppose you only want to retrieve specific columns, such as "id" and "username," from the "User" table. The following code snippet won't suffice:

Post::query()
    ->with('user')
    ->get();

To accomplish your goal, you can pass a closure function as the second index of the array passed to the "with()" function:

Post::query()
    ->with(['user' => function ($query) {
        $query->select('id', 'username');
    }])
    ->get()

This closure allows you to specify which columns to retrieve from the second table. In this instance, it will only select the "id" and "username" columns from the "User" table.

Note: As mentioned in the answer, the primary key ("id" in this case) must be the first parameter in the $query->select() method to ensure proper results retrieval.

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