Relationships & Validation

Relationships

Eloquent makes relationships effortless. Define them once on the model, then access related data like a property.

// In the User model
public function posts() {
    return $this->hasMany(Post::class);
}

// In the Post model
public function user() {
    return $this->belongsTo(User::class);
}

You declare the link once on each model. In the User model, hasMany(Post::class) says "one user owns many posts". In the Post model, belongsTo(User::class) says "each post belongs to one user". These two methods describe the same relationship from both sides.

With those defined, you reach related data as if it were a normal property — no JOIN to write:

$user = User::find(1);
$user->posts;          // all of this user's posts — no JOIN written!

$post = Post::find(1);
$post->user->name;     // the post's author name

Because we named the method posts() on the User model, $user->posts gives back that user’s posts. Going the other way, $post->user gives the post’s owner, and $post->user->name steps straight to that owner’s name. Eloquent runs the database query for you behind that simple dot.

Validation

Validation means checking the user’s input is acceptable *before* you save it — for example, the name must not be empty and the price must be a number. Laravel does this in one line:

public function store(Request $request)
{
    $validated = $request->validate([
        'name'  => 'required|max:100',
        'price' => 'required|numeric|min:0',
    ]);
    Product::create($validated);
    return redirect('/products');
}

The $request->validate([...]) call lists each field and its rules as a simple string: 'required|max:100' means "must be present and at most 100 characters", and 'required|numeric|min:0' means "must be present, a number, and not negative". If every rule passes, the clean values come back in $validated and you save them. If any rule fails, Laravel stops, sends the user back to the form, and shows the error messages — you write no if checks at all.

How a validated form submission flows:

1. The user submits the form and the request reaches the store method.
2. $request->validate([...]) checks each field against its rules.
3. If a rule fails, Laravel automatically redirects back to the form with error messages — your saving code never runs.
4. If all rules pass, the clean data is returned and you save it with Product::create($validated).
5. Finally you redirect the user on to the next page.