# Demystify Eager Loading

Eager loading is a technique in Laravel to load relationships efficiently. When you retrieve a model, you can specify which relationships should be loaded with it. This reduces the number of queries needed to fetch related models, enhancing performance.

Eager loading is accomplished using the with method. You pass the name of the relationship you want to load as an argument. For example, if you have a Post model that has a comments relationship, you can load the comments relationship like this:

# What is the difference between with and load?

The with method is used to eager load relationships when retrieving a model. In contrast, the load method is used to eager load relationships on an already retrieved model instance.

For example, if you want to load the comments relationship when retrieving a Post model, you can use the with method like this:

$post = Post::with('comments')->find(1);

If you already have a Post model instance (for example, from route model binding) and you want to load the comments relationship, you can use the load method like this:

$post->load('comments');

Another example;

public function mount(StudentCourse $studentCourse)
{
    // This gives you the entire student course instance with no related courses loaded.
    $sc = $studentCourse;

    // This returns all student courses and loads the related courses, which is not what you want.
    $sc = $sc->with('course')->get(); // Not ideal, retrieves all records

    // This correctly fetches a single student course by ID but does not eager load the course.
    $sc = $sc->with('course')->find($studentCourse->id); // Would not actually eager load

    // This is the right way to eager load the related course for the already existing student course instance.
    $sc = $sc->load('course'); // Correctly loads only the related course for the specific student course
}

# Trouble Shooting

When you are ripping your hair out because eager loading is not working as expected, here are a few things to check:

Correct Syntax for Selecting Columns

Ensure there are no spaces after commas in the column selection syntax.

// Correct
$studentCourse = $studentCourse->load('course:id,title');

// Incorrect
$studentCourse = $studentCourse->load('course:id, title');

Include the Foreign Key in the Relationship Definition

Make sure to include the foreign key in the eager loading statement.

// Correct
$studentCourse = $studentCourse->load('course:id,title');

// Incorrect
$studentCourse = $studentCourse->load('course:title');

Eager Loading Nested Relationships

When eager loading nested relationships, always include the foreign keys of the child models as well.

// Correct
$studentCourse = $studentCourse->load([
    'course:id,title',
    'course.modules:id,title,course_id',
]);
// Incorrect
$studentCourse = $studentCourse->load([
    'course:id,title',
    'course.modules:id,title',
]);