Get property of relation in model - laravel

Question

class Ingredient extends Eloquent {
public function unit() {
return $this->hasOne('IngredientUnit', 'id', 'unit_id');
}
}
class IngredientUnit extends Eloquent {
public function ingredient() {
return $this->belongsTo('Ingredient', 'unit_id', 'id');
}
public function getNamesAttribute() {
$quantity = $this->ingredient()->quantity; // <- ErrorException
...
}
}
ErrorException (E_UNKNOWN):
Undefined property: Illuminate\Database\Eloquent\Relations\BelongsTo::$quantity
If I remove brackets - $this->ingredient->quantity; - I get
ErrorException (E_UNKNOWN)
Trying to get property of non-object
How can I get property of relation object (belongsTo) ?
Schemas:
Schema::create('ingredients', function(Blueprint $table)
{
$table->increments('id');
$table->integer('recipe_id')->unsigned();
$table->integer('unit_id')->unsigned()->nullable();
$table->float('quantity')->unsigned();
...
});
Schema::create('ingredient_units', function(Blueprint $table)
{
$table->increments('id');
$table->string('name');
...
});

Answer 1

With these tables your relations are wrong.
You need to swap them, for it goes like this: unit hasOne/hasMany ingredients, ingredient belongsTo unit.
// Ingredient
public function unit()
{
return $this->belongsTo('IngredientUnit', 'unit_id', 'id');
}
// IngredientUnit - I don't think it's hasOne, rather hasMany
public function ingredients()
{
return $this->hasMany('Ingredient', 'unit_id', 'id');
}
Next, this can't work:
$this->ingredient()->quantity;
but this will work, as long as there is model returned from the relation:
$this->ingredient->quantity;
So basically you don't have related ingredient, that's why it returns null and your get the error.

Answer 2

First you should change:
$quantity = $this->ingredient()->quantity;
into
$quantity = $this->ingredient->quantity;
But in case no Ingredient is found, you get exception, so you should better change it into:
$ingredient = $this->ingredient;
$quantity = ($ingredient) ? $ingredient->quantity : 0;
to assign 0 if no ingredient is found;