How addSelect() Builder method works in Laravel

问题

Say I have these models:

User Model

namespace App;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
    /**
     * The table associated with the model.
     *
     * @var string
     */
    protected $table = 'User';

    protected $fillable =
    [
       'username', 'favoriteColor'
    ];          

    public function flights()
    {
        return $this->hasMany('App\Flight');
    }
}

Flight Model

namespace App;

use Illuminate\Database\Eloquent\Model;

class Flight extends Model
{
    /**
     * The table associated with the model.
     *
     * @var string
     */
    protected $table = 'Flight';

    protected $fillable =
    [
       'flightName', 
    ];              
}

I'm trying to do something with eager loading, whenever I do this:

$usersWithFlights = User::with(['flights'])->get();

I get data like this: (Which if fine, is what I expect)

{
    "userID": 1,
    "favoriteColor": green
    "flights": 
    [
       {
           "flightID": 2240,
           "flightName" : "To Beijing fellas"
       },
       {
           "flightID": 4432,
           "flightName" : "To Russia fellas"
       },       
    ]
}

But then I want to add a column using a select raw like this: (Don't think about how silly the 1 as number is, it's just for the sake of the example.

$usersWithFlights = User::with(['flights'])->addSelect(DB::raw('1 as number'))->get();

I get the data like this:

[
    {
        "userID": 1,
        "favoriteColor": green
        "flights": []
    }
]

QUESTION

Was the addSelect() method made for this kind of behaviour? If not are other work arounds in order to achieve this?

NOTE

I know I could add in the select method something like Flights.*, Users.* but I want to know if the addSelect method works that way

回答1:

If you need default values from select and add some extra, you can use this construction:

$usersWithFlights = User::with(['flights'])->select()->addSelect(DB::raw('1 as number'))->get();

回答2:

At first take a look at the addSelect method:

public function addSelect($column)
{
    $column = is_array($column) ? $column : func_get_args();
    $this->columns = array_merge((array) $this->columns, $column);
    return $this;
}

This just adds the column(s) by merging with existing selected columns. So, when you use something like this:

$usersWithFlights = User::with(['flights'])->addSelect(DB::raw('1 as number'))->get();

The query becomes select 1 as number from flights and since your relation depends on a column value in the parent query so without any real column value there are no related records retrived. To check the queries you may try something like this:

\DB::enableQueryLog();
$usersWithFlights = User::with(['flights'])->addSelect(DB::raw('1 as number'))->get();
dd(\DB::getQueryLog());

Also, if you use a real column name in add select and if you don't select the related column for example, if you use addSelect('someString') then you'll get no related records either because you've to also select the related column that makes the relation and in this case you may try something like this:

$usersWithFlights = User::with(['flights'])->addSelect(['id', 'someString']))->get();

Test:

This is a test result of DB::getQueryLog() where I've used something similar but with different tables in my DB which is:

Post->with('comments')->addSelect(DB::raw('1 as number'))->get();
dd(DB::getQueryLog());

Result:

0 => array:3 [▼
  "query" => "select 1 as number from "posts""
  "bindings" => []
  "time" => 9.0
  ]
1 => array:3 [▼
  "query" => "select * from "comments" where "comments"."post_id" in (?)"
  "bindings" => array:1 [▼
    0 => null
  ]
  "time" => 1.0
]

Update:

The addSelect method is usefull when you've a query object at hand with some selected fields and later you want to add more fields in the select list so aan example could be like this:

$userWithFlights = User::with('flights')->select(['id', 'someColumn']);
// Some code ... 
if(SomeCondition) {
    // So, now the query will be something like this:
    // ->select(['id', 'someColumn', 'anotherField'])
    $userWithFlights->addSelect('anotherField');
}

$result =  $userWithFlights->get();

If you want to specifi some fields to be selected then you may use select($fieldsArray) instead. You may also try something like this:

$userWithFlights = User::with('flights')->get(['id', 'someColumn']);

Also you may try something like this:

$userWithFlights = User::with(['flights' => function($query) {
    $query->select('user_id', 'flight_title');
}])->get(['id', 'someColumn']);

来源：https://stackoverflow.com/questions/36345690/how-addselect-builder-method-works-in-laravel

标签

php

laravel

laravel-5

eager-loading