Laravel Eloquent pass variable to with relationship function
Stefan Bogdanescu
Founder & Senior Architect · 2026-06-29
# Mastering Dynamic Filtering in Eloquent: Passing Variables into `with()` Relationships
As senior developers working with Laravel and Eloquent, we constantly face scenarios where we need to perform complex data retrieval. One common challenge arises when trying to apply dynamic filtering—like date ranges or specific IDs—to related models that are being eagerly loaded using the `with()` method.
The core issue you are encountering is how to inject a variable from the main query scope into the constraint applied to a nested relationship defined within the `with()` clause. Let's break down why this happens and the correct, idiomatic way to achieve dynamic relationship filtering in Eloquent.
## The Challenge: Scoping Eager Loaded Relationships
You are attempting to filter the related tasks based on a `$date` variable when eager loading a relationship. Your attempt using a closure within `with()` is conceptually correct, but understanding the context of how Eloquent processes these nested queries is crucial.
Your provided example highlights two distinct ways of querying:
1. **Direct Querying:** Applying constraints directly to the main query (`TaskAssignment::where('dueDate', $date)->get()`). This is straightforward because all constraints live on the primary model being fetched.
2. **Eager Loading Scoping:** Applying constraints inside a `with()` closure, which scopes the filtering specifically to the relationship being loaded.
The confusion often stems from thinking that the variable `$date` must be passed directly into the outer query builder, rather than realizing that the closure provides access to the scope necessary for the inner query.
## The Solution: Using Closures for Relationship Constraints
The correct approach for dynamic filtering on eager-loaded relationships is indeed using a closure within `with()`. This closure receives an instance of the query builder (the `$query` variable in your example) that is specifically scoped to load the related data. By modifying this internal `$query`, you effectively constrain the relationship query *before* it is loaded into memory.
Let’s examine your specific case for the `teacher` scenario:
```php
// Example of the problematic structure:
$allTasks = Tasks::where('teacher_id', $myTid)
->with(['assignment' => function ($query) use ($date) { // Note: 'use ($date)' is often required if outside helper methods
$query->where('dueDate', $date);
$query->orderBy('dueDate', 'asc');
}
])-->get();
```
### Deeper Dive into the Mechanism
When you define a relationship using `with(['relationship' => function ($query) { ... }])`, Eloquent executes two distinct operations:
1. **The Outer Query:** Fetches the primary models (e.g., `Tasks`).
2. **The Eager Loading Operation:** For each model fetched, Eloquent initiates a separate query to load the specified relationships. The closure you define is executed *within* this eager loading context. By calling methods like `where()` or `orderBy()` on `$query` inside the closure, you are modifying that subordinate query, ensuring that only tasks matching the required date are retrieved for that specific teacher's assignments.
This technique demonstrates Eloquent’s power in handling complex data relationships efficiently. For more advanced structuring and reusability of these constraints across your application, consider leveraging **Local Scopes**, as highlighted by best practices found on sites like [Laravel Company](https://laravelcompany.com). Local scopes allow you to define reusable query constraints directly on your models, making your code cleaner and more maintainable than embedding complex logic deep within service methods.
## Best Practices: When to Use Scopes vs. Closures
While the closure method works perfectly for dynamic, runtime filtering based on variables, it's important to understand when to use other Eloquent features:
1. **Closures (Dynamic Filtering):** Ideal for scenarios where the filter criteria (like `$date`) is determined dynamically at runtime and is specific to a single request or operation.
2. **Local Scopes (Reusable Constraints):** Use these when you have standard, reusable filtering logic that should be applied consistently across many different queries involving a model (e.g., defining `scopeDueTasks($date)` on the `Task` model). This keeps your controller and service layers very clean.
For instance, instead of nesting the date logic in every service method, you would define a scope:
```php
// In Task Model
public function scopeDue($query, $date)
{
return $query->where('due_date', $date);
}
```
Then, your query becomes much cleaner:
```php
$allTasks = Tasks::where('teacher_id', $myTid)
->with(['assignment' => function ($query) {
$query->due($date); // Using the defined scope
}])
->get();
```
## Conclusion
Passing variables into Eloquent `with()` relationships is not only possible but is a powerful feature of the framework, allowing you to construct highly specific and efficient database queries. By understanding that the closure provides access to an inner query builder, you can effectively constrain your eager loading. For production systems, remember to balance dynamic runtime filtering (using closures) with reusable structural logic (using Local Scopes) to maintain the cleanest and most scalable codebase possible.