Laravel 雄辩地从连接表中选择最近的行 [英] Laravel eloquent selecting most recent row from joined table

问题描述

我有两个表，Project 和 Projectnote

I have two tables, Project and Projectnote

project 和 projectnote 之间存在一对多的关系.

There is a one to many relationship between project and projectnote.

我希望能够列出我的项目并根据 created_at 日期选择最新的项目笔记.

I want to be able to list my projects and select the most recent projectnotes based on the created_at date.

这是否可以在 Eloquent 中实现，我无法弄清楚.

Is this possible to do in Eloquent, I can't figure it out.

感谢您的帮助！

到目前为止，我有一个连接两个表的基本查询(如下).但是，这仅选择存在注释的项目，并且我得到多个行，其中每个项目有多个注释.

so far I have a basic query (below) that joins the two tables. However, this only selects projects where a note exists and I get multiple rows where there are several notes per project.

$projects = Project::join('projectnotes', 'projectnotes.project_id', '=', 'projects.id')
->select(array('projects.*', 'projectnotes.note as note'))
->get();

推荐答案

可以加入最新值的表格:

You can join the table on the latest value:

->join('t1', function($join) {
        $join->on('t1.t2_id', '=', 't2.id')
             ->on('t1.id', '=', DB::raw("(select max(id) from t1 WHERE t1.t2_id = t2.id)"));

如果您还想在 t1 没有值的地方加入，请使用 leftJoin.在您的情况下，这看起来像这样:

If you also want to join where t1 does not have a value, use a leftJoin. In your case this would look like this:

$projects = Project::leftJoin('projectnotes', function($join) { 
        $join->on('projectnotes.project_id', '=', 'projects.id')
             ->on('projectnotes.id', '=', DB::raw("(SELECT max(id) from projectnotes WHERE projectnotes.project_id = projects.id)")); 
        })
        ->select(array('projects.*', 'projectnotes.note as note'))

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