Cannot access Eloquent attributes on Twig - php

Question

I am trying to access an Eloquent attribute with Twig in Slim, and getting an error.
I have a Field and a Type object, and the relationship is as follows
class Field extends \Illuminate\Database\Eloquent\Model {
protected $table = 'fields';
public function type()
{
return $this->belongsTo('models\Type');
}
When doing {{ f }} (being f a field), the output is this:
{"field_id":"1","field_name":"Your name","form_id":"2","type_id":"1","placeholder":"Please give us your name"}
And when doing {{ f.type }}, the result is:
Message: An exception has been thrown during the rendering of a template ("Object of class Illuminate\Database\Eloquent\Relations\BelongsTo could not be converted to string") in "pages/editform.html" at line 97.
If I try to do {{ f.type.name }}, doesn't throw up an exception but doesn't print anything either.
If I do it in PHP
$fields = $form->fields;
var_dump($fields[0]->type->name);
The value gets output correctly.
Any ideas?,
Thanks

Answer 1

If you don't want to do an eager load, you can override the magic __isset method in your Field class to return true for the type relationship property:
public function __isset($name)
{
if (in_array($name, [
'type'
])) {
return true;
} else {
return parent::__isset($name);
}
}
Explanation
The problem is in the interaction between how Eloquent implements the "dynamic property" for a relation (in your case, f.type), and the rules that Twig uses for accessing "attributes" of a variable.
From the Twig documentation:
For convenience's sake foo.bar does the following things on the PHP layer:
check if foo is an array and bar a valid element;
if not, and if foo is an object, check that bar is a valid property;
if not, and if foo is an object, check that bar is a valid method (even if bar is the constructor - use __construct() instead);
if not, and if foo is an object, check that getBar is a valid method;
if not, and if foo is an object, check that isBar is a valid method;
if not, return a null value.
foo['bar'] on the other hand only works with PHP arrays:
check if foo is an array and bar a valid element;
if not, return a null value.
The key here is the part where it says "check that bar is a valid property". This means that on the level of PHP, Twig is calling isset on $f->type. Eloquent implements the magic __isset method in Model, so you might think that this wouldn't be a problem.
However, take a look at how it actually implements __isset for model relations:
/**
* Determine if an attribute exists on the model.
*
* #param string $key
* #return bool
*/
public function __isset($key)
{
return (isset($this->attributes[$key]) || isset($this->relations[$key])) ||
($this->hasGetMutator($key) && ! is_null($this->getAttributeValue($key)));
}
It determines whether a relation is "set" by looking in its array of loaded relationships (isset($this->relations[$key])). The problem is that if type hasn't been loaded yet, Eloquent will say that it is not "set".
Thus when Twig looks at $f->type, it will think that type is not a valid property, and move on to the next rule:
...if foo is an object, check that bar is a valid method
So now it will look for the method type(), which it finds. The only problem? type() (the method) returns a Relation (specifically, a BelongsTo), rather than a Type object. And BelongsTo objects aren't models.
If you want Twig to know that the property $f->type does indeed exist, you have two choices:
You can eager-load the related Type object along with your Field, as suggested by #roger-collins, or;
You can overload the __isset magic method in Field:
public function __isset($name)
{
if (in_array($name, [
'type'
])) {
return true;
} else {
return parent::__isset($name);
}
}
This will force Twig to recognize that type is a valid property for Field, even before the related model has actually been loaded.

Answer 2

I had the same issue and stumbled upon this question. After solving it myself, I thought I'd try to help you out.
Try doing a Eager Load on the model:
Field::with('type')->get()
This should allow you to do the following with no other issues.
{{ f.type }}
See more info here: http://laravel.com/docs/4.2/eloquent#eager-loading