Fetch specific fields on a hasMany relation
Stefan Bogdanescu
Founder & Senior Architect · 2026-06-29
# Mastering Eager Loading: How to Fetch Only Specific Fields from a `hasMany` Relation
As developers working with Eloquent and Laravel, eager loading (`with()`) is one of the most powerful features we have for optimizing database queries. We use it to prevent the N+1 problem by fetching related data in bulk. However, sometimes, simply fetching *all* columns from a relationship results in over-fetching—pulling unnecessary data that slows down your application and increases memory consumption.
This post addresses a very common scenario: how do we instruct Eloquent to fetch only a subset of fields from a `hasMany` relationship without manually iterating through the results after the query returns? We will explore the mechanism behind constrained relationships and demonstrate the best practice for optimizing data retrieval in Laravel.
## The Problem: Over-fetching Data via Eager Loading
Let's start by looking at the standard way we handle relationships. Suppose we have a `User` model with a `hasMany` relationship to an `Article` model.
When you use eager loading, Eloquent fetches all necessary data. If the related model (`Article`) has many columns, they are all loaded into memory, even if you only need two or three fields for display.
**The Initial Scenario:**
You start with this setup:
```php
// In User Model
public function articles()
{
return $this->hasMany('App\Article');
}
```
And when you load the data:
```php
$data = \App\User::with('articles')->get();
```
The result includes all columns for every article, which is often more than necessary:
```json
{
"id": 1,
"name": "Jhon",
"lastname": "Doe",
"articles": [
{
"id": 1,
"title": "Article 1",
"status": "published",
"published_at": "2015-04-30" // Unwanted fields included here
},
// ... other articles
]
}
```
Your goal is to refine this to only return the essential data: `id` and `title` for each article.
## The Solution: Constrained Relationships
The key to solving this efficiently lies in defining **constrained relationships** on your Eloquent models. This mechanism allows you to specify which columns should be selected whenever that relationship is loaded, effectively filtering the data at the database level during the eager loading process.
Instead of relying solely on the parent model's definition, we need to modify the relation definition within the related model itself.
### Step 1: Constraining the Relation in the Related Model
We must go into the `Article` model and redefine how it interacts with its parent. We use the `with()` method inside the relationship definition to scope the selection.
**In `app/Models/Article.php`:**
```php
hasMany(Article::class)->select('id', 'title');
}