Add custom attribute in eloquent model

Question

Here is a raw SQL query:

SELECT name, area, point(area) AS center FROM places;

I want to get an Eloquent model based on this query. Here is the Model:

class Place extends Model
{
    protected $visible = ['name', 'area'];
}

So, I want to get the center property if I run this code:

return response()->json( Place::all() );

center is missing. I don't know how to add the center property in my Place object. I don't want to build a raw query in my controller, is there any solution with mutator or something like this? (The only thing I want to call is Place::all(), I really want to use Eloquent Model in controllers, not an SQL query).

Amelia · Accepted Answer · 2015-07-06 10:04:45Z

6

Use a combination of Mutators and the $appends property. Here's an example:

<?php namespace App;

use Illuminate\Database\Eloquent\Model;

class Place extends Model {

    protected $appends = ['center'];

    public function getCenterAttribute()
    {
        return $this->point($this->getRawAttribute("area"));
    }

    protected function point($area)
    {
        // logic for SQL POINT(), etc
    }
}

The $appends property will mean that the mutated attribute is included in JSON/array output when $model->toJson() or $model->toArray() is called (which Response::json() does)

The reason for doing point logic in code is because with eloquent models, you'd hit the N+1 query problem when fetching a list of places and their centers, and that's not a great idea for your database.

Your query wouldn't be used when fetching data for the model from the database, either, since the default query for models is

select * from `table` where id = :id

Which is then figured out internally to set up data on the model.

edited Jul 6, 2015 at 10:04

answered Jul 6, 2015 at 9:36

Amelia

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3 Comments

rap-2-h Over a year ago

Ok, thanks a lot! I'm not sure to understand everything yet; so i can't use the "power" of postgresql for this? (it can transform polygon to a center point). I have to write a custom php code for this?

Amelia Over a year ago

You can technically use a custom query, but it still has performance penalties. I can't remember if raw expressions are allowed in $columns; i'll check that now

Chintan7027 Over a year ago

But when i save the object which contains appended field then it will going to update the filed. How to prevent that ?

Maksym · Accepted Answer · 2015-07-06 09:22:34Z

0

You may want to take a look at this: http://laravel.com/docs/5.0/eloquent#global-scopes. It should help you build the query that will always get center along with the rest of data.

edited Jul 6, 2015 at 9:22

answered Jul 6, 2015 at 8:56

Maksym

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2 Comments

Ben Swinburne Over a year ago

OP has tagged laravel-5 in which they're implemented slightly differently if I recall correctly. Might want to update with the correct docs.

Ben Swinburne Over a year ago

In addition, OP may not need to use a global scope if they're happy with doing Place::center()->get();. Normal scopes are much quicker to implement and slightly more verbose for those looking at code later.

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