Laravel belongsToMany relationship with only one result

Question

I have a relationship between two tables with a join table that only has one result.

When I define a Laravel belongsToMany relationship, instead of returning a collection with only one element I would like to have it return that item alone.

Is there a way to model this in Laravel?

Thanks in advance.

[EDIT]

I'll try to explain what I want using the classic Users/Roles example. Besides de users and roles tables, we'll have a users_roles pivot table which will store all the roles the user has had. A user can, at any given time, have only one active role (identified by the active attribute being true).

class User {
    function role() {
        return $this->belongsToMany('App\Role')->wherePivot('active', 'true');
    }
}

With this relationship definition, when I access $user->role I get a collection (with only one element) of Roles. What I would like is to have that Role instance directly.

Answer 1

I have written a more generic approach to solving this issue. The downside to it is that I had to copy code from the laravel/frame vendor files. So this might break someday when upgrading Laravel Framework.

use Illuminate\Contracts\Support\Arrayable;
use Illuminate\Support\Str;

/**
 * Based on laravel/framework@8.54.0
 */
trait SupportsSingleResultBelongsToMany
{
    /**
     * Get the model's relationships in array form.
     *
     * @return array
     */
    public function relationsToArray()
    {
        $attributes = [];

        foreach ($this->getArrayableRelations() as $key => $value) {
            // If the values implements the Arrayable interface we can just call this
            // toArray method on the instances which will convert both models and
            // collections to their proper array form and we'll set the values.
            if ($value instanceof Arrayable) {
                if (isset($this->forceSingleResult) &&
                    in_array($key, $this->forceSingleResult) &&
                    $value instanceof \ArrayAccess &&
                    $value instanceof \Countable
                ) {
                    $relation = count($value) > 0 ? $value[0] : null;
                } else {
                    $relation = $value->toArray();
                }
            }

            // If the value is null, we'll still go ahead and set it in this list of
            // attributes since null is used to represent empty relationships if
            // if it a has one or belongs to type relationships on the models.
            elseif (is_null($value)) {
                $relation = $value;
            }

            // If the relationships snake-casing is enabled, we will snake case this
            // key so that the relation attribute is snake cased in this returned
            // array to the developers, making this consistent with attributes.
            if (static::$snakeAttributes) {
                $key = Str::snake($key);
            }

            // If the relation value has been set, we will set it on this attributes
            // list for returning. If it was not arrayable or null, we'll not set
            // the value on the array because it is some type of invalid value.
            if (isset($relation) || is_null($value)) {
                $attributes[$key] = $relation;
            }

            unset($relation);
        }

        return $attributes;
    }
}

Then in your model, just use the Trait and specify which relations are single result.

class MyModel extends Model
{
    use SupportsSingleResultBelongsToMany;

    protected $forceSingleResult = ["teams"];

    public function teams()
    {
        $this->belongsToMany(Team::class);
    }
}

Answer 2

In my case that was the most straight forward solution:

class User extends Model {

    public function services()
    {
        return $this->belongsToMany(Service::class, 'service_user')
                    ->using(ServiceUser::class)
                    ->withPivot('user_id', 'service_id', 'is_main_service');
    }

    public function mainService()
    {
 
        return $this->hasOneThrough(Service::class, ServiceUser::class, 'user_id', 'id', 'id', 'service_id')
                    ->where('is_main_service', 1);
    }
}

Pivot table class:

use Illuminate\Database\Eloquent\Relations\Pivot;

class ServiceUser extends Pivot
{
    
}

Answer 3

I faced this issue, and have found a really clean way to solve it.

First, change the name of the accessor function that returns the belongsToMany result to reflect the fact that these return multiple results. In your case this would mean using roles instead of role:

function roles() {
  return $this->belongsToMany('App\Role')->wherePivot('active', 'true');
}

Then add the following to your model:

protected $appends = ['role'];

public function getRoleAttribute() {
  return $this->roles()->first();
}

Now, when you call $user->role you'll get the first item.

Answer 4

Laravel Eloquent works on the principle of magic. You can override the magic method __get. If there is no property, the __get method is called:

(in your model)

    public function __get ($name)
    {
        $answer = parent::__get($name);
        if($name=='your_prop'){
            $answer=!empty($answer)?$answer[0]:null;
        }
        return $answer;
    }

If your your_prop to-many relationship returns anything take the first in the array.

Answer 5

I don't know why you have belongsToMany if you need only one relation, however below code will help you:

public function products()
{
    return $this->belongsToMany('App\Product');
}

public function specific_product()
{
    return $this->products()
                ->where('column','value')->first();
}

OR

public function getSpecificProductAttribute()
{
    return $this->products()
                ->where('column','value')->first();
}

Answer 6

I faced the exactly same issue, let me show you how I managed it.

In my case a have a belongsToMany relationship between materials and customer_types, the pivot table contains the material price for specific customer types, therefore there are as many records (prices) in the pivot table as customer_types are.

What I expected: when a price is requested for a specific customer_type I want to get the scoped price for that specific customer_type as a nested element.

What I got: a collection with only 1 element.

This is what I had at the beginning in my Model:

class Material extends Model
{
    public function customer_types(){
        return $this->belongsToMany('App\CustomerType', 'customertype_material', 'material_id', 'customertype_id')->withPivot('price');
    }
}

Of course, when I requested the customer_types for a specific customer_type the result wasn't the expected one:

$resources = Material::with(['customer_types' => function($query) use ($customer_type_id){
                        $query->where('customertype_id', $customer_type_id);
                       }])->get();

It was returning a Material model with a customer_types nested collection with 1 element on it, forcing me to use first() or loop over 1 element.

The solution: Create a Model that extends the pivot table and add a relationship to it.

Created a new model that extends the pivot:

use Illuminate\Database\Eloquent\Relations\Pivot;

class CustomertypeMaterial extends Pivot
{
    protected $table    = 'customertype_material';
    protected $fillable = ['price', 'customertype_id', 'material_id'];
}

Now, added a relationship pointing to this new model in my Material Model:

public function scoped_price(){
    return $this->belongsTo('App\CustomertypeMaterial', 'id','material_id');
}

Finally the query loading this new relationship:

$resources = Material::with(['scoped_price' => function($query) use ($customer_type_id){
                        $query->where('customertype_id', $customer_type_id);
                       }])->get();

The result is a Material model with a scoped_price element nested on it and filtered by a customer_type_id

I'm not sure if it's the right way to do this, but it's working for me.

Hope it helps!