Select specific fields from array of Eloquent collecton | Laravel - php

Question

I have a collection object which includes the array of Model objects and I would like to select specific fields from the model.
Illuminate\Database\Eloquent\Collection Object
(
[items:protected] => Array
(
[0] => App\Model Object
[1] => App\Model Object
[2] => App\Model Object
)
)
Now I would like to select some fields from the model object. When I try to do the following syntax
print_r($collection->select('filed a', 'field b'));
then the following error occurs.
BadMethodCallException in Macroable.php line 74: Method select does
not exist.
I think select can work directly with the eloquent model but not with a collection.

Answer 1

Are you looking for only()
$filtered = $collection->only(['list', 'of', 'fields', 'to', 'keep']);
or perhaps mapWithKeys()

Answer 2

You are correct that select is not present on the Collection class.
What you can do is map, filter or transform the collection yourself e.g.
$whiteList = ['filed a', 'field b'];
$filledOnly = $collection->map(function ($item) use ($whiteList) {
$properties = get_object_vars($item);
foreach ($properties as $property) {
if(!in_array($property, $whiteList) {
unset($item->{property});
}
}
return $item;
});
The problem is in PHP once a property (or field) is set on an object, you really have to unset it or create new objects of the same class). This is why I came up with this solution.
Question is: How did you retrieve this collection in the first place, could you not add the select to the query itself?

Answer 3

The best would have been to select the fields you need before you execute the query on the model. However, you can use map() if you want to preserve the initial collection or transform() if you want to override the collection (for example):
$selected_fields = ['filed a', 'field b']
$models->map(function ($zn) use ($selected_fields) {
return $zn->newInstance(array_only($zn->getAttributes(), $selected_fields));
})->toArray();
newInstance() method creates a new empty instance of that model then getAttributes() retrieves the attributes present in the model. So the initial model is preserved in this process.
For reference sake, the implementation of newInstance() can be found on at Illuminate\Database\Eloquent\Model class and it is as follows (on Laravel 5.2):
/**
* Create a new instance of the given model.
*
* #param array $attributes
* #param bool $exists
* #return static
*/
public function newInstance($attributes = [], $exists = false)
{
// This method just provides a convenient way for us to generate fresh model
// instances of this current model. It is particularly useful during the
// hydration of new objects via the Eloquent query builder instances.
$model = new static((array) $attributes);
$model->exists = $exists;
return $model;
}