Question

我对laravel关系感到非常惊讶，因为它与左联接相比可以提供没有重复条目的结果。例如最近我尝试自连接对同一张表有很多

 public function parentMenu(){
        return $this->hasMany(Page::class,'parent_page_id','id');
    }

它返回以下结果

Array
(
    [0] => Array
        (
            [id] => 1
            [page_name] => Branch Details
            [page_url] => #
            [parent_page_id] => 0
            [page_type] => 1
            [created_at] => 2018-06-23 23:45:34
            [updated_at] => 2018-06-23 23:45:34
            [deleted_at] => 
            [slug] => branch_detail
            [parent_menu] => Array
                (
                    [0] => Array
                        (
                            [id] => 2
                            [page_name] => Add Branch Detail
                            [page_url] => add-branch
                            [parent_page_id] => 1
                            [page_type] => 1
                            [created_at] => 2018-06-23 23:45:54
                            [updated_at] => 2018-06-23 23:45:54
                            [deleted_at] => 
                            [slug] => add_branch_detail
                        )

                    [1] => Array
                        (
                            [id] => 11
                            [page_name] => View Branch Detail
                            [page_url] => list-branch
                            [parent_page_id] => 1
                            [page_type] => 1
                            [created_at] => 2018-06-23 23:46:08
                            [updated_at] => 2018-06-23 23:46:08
                            [deleted_at] => 
                            [slug] => 
                        )

                )

        )

我也试图找出查询内容

Array
(
    [0] => Array
        (
            [query] => select * from `pages` where `pages`.`deleted_at` is null
            [bindings] => Array
                (
                )

            [time] => 0.82
        )

    [1] => Array
        (
            [query] => select * from `pages` where `pages`.`parent_page_id` in (?, ?, ?, ?, ?, ?, ?, ?, ?, ?) and `pages`.`deleted_at` is null
            [bindings] => Array
                (
                    [0] => 1
                    [1] => 2
                    [2] => 4
                    [3] => 5
                    [4] => 7
                    [5] => 8
                    [6] => 9
                    [7] => 10
                    [8] => 11
                    [9] => 12
                )

            [time] => 0.86
        )

)

现在我的问题是如果我尝试获得相同的结果，那将是mysql查询。因为我想知道内部关系查询的工作原理？它将在内部执行forloop还是在查询本身中产生结果。

它还会循环执行单独的查询以检索子菜单列表吗？

Answer 1

Laravel的活动记录实现不使用联接来建立关系（它们中的某些关系也使用联接，但这适用于belongsToMany之类的需要使用枢轴/中间表的关系）。

实际发生的是Eloquent将从表中获取相关键并执行另一个查询以获取所需的关系，例如

Post有许多Comment，并且数据库中有3个ID为1，2和3的帖子。

Post::with('comments')->get();

将导致：

查询1

SELECT * from `posts`

查询2

SELECT * FROM `comments` WHERE `comment`.`post_id` in ('1', '2', '3')

它将检查第二个查询的结果，并将其与从第一个查询加载的模型进行匹配。

如果您想查看正在从Laravel应用程序中运行什么查询，那么我建议安装其中一个：

除其他外，这两个工具都可以向您显示正在运行的查询。

laravel关系在内部如何运作？

1 个答案: