如何在 Laravel 5.3 中创建两次连接到表的查询?

How to create query with twice a connection to a table in Laravel 5.3?(如何在 Laravel 5.3 中创建两次连接到表的查询?)

问题描述

我需要通过一个查询获得两个城市名称:

I need get two city names with one query:

例如:

城市表:

+---------+----------+
|  Pana   |   Name   |
+---------+----------+
|   THR   |  Tehran  |
|   LON   |  London  |
+---------+----------+

在模型中:from_city 是 THR，to_city 是 LON

In Model: from_city is THR and to_city is LON

public function scopePrintQuery($query, $id)
{
    $join = $query
        -> join('cities', 'cities.pana', 'flights.from_city')
        -> join('cities', 'cities.pana', 'flights.to_city')
        -> where('flights.id', $id)
        ->get([
            'flights.*',
            'cities.name as from_city'
            ??? for to_city?
        ]);
    return $join;
}

现在，我需要在此查询中获取 from_city 名称和 to_city 名称.

Now, I need get from_city name and to_city name in this query.

该查询不适用于一张表中的两个连接！

The query does not work with two joins from one table!

如何创建这个查询?

推荐答案

使用直接的 SQL 你可以给每个连接的表一个别名 - 例如

With straight SQL you could give each joined table an alias - e.g.

SELECT flights.*
FROM flights as f
 JOIN cities as fromCity on fromCity.pana = f.from_city
 JOIN cities as toCity on toCity.pana = f.to_city
WHERE f.id = 3 --

对于 Eloquent，使用 select() 来指定选择字段.还可以使用 DB::raw() 来使用原始 SQL(例如给出一个表的别名，如 DB::raw('cities as toCity').

With Eloquent, use select() to specify select fields. Also use DB::raw() to use raw SQL (e.g. giving an alias to table like DB::raw('cities as toCity').

public function scopePrintQuery($query, $id)
{
  $join = $query
    -> join(DB::raw('cities as fromCity'), 'fromCity.pana', 'flights.from_city')
    -> join(DB::raw('cities as toCity'), 'toCity.pana', 'flights.to_city')
    -> where('flights.id', $id)
    ->select([
        'flights.*',
        DB::raw('fromCity.name as from_city')
        DB::raw('toCity.name as to_city')
    ]);
    return $join->get();
}

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