Laravel 5.2 急切负载关系与汇总计算

Question

I am working on a simple tasks app. I want to eager load the total time spent for each project. I have two tables:

Table: task_project 
id, client_id, name, description

Table: task_entries
id, task_project_id, start_time, end_time

The relationship between tables is established via task_project.id = task_entries.task_project_id .

For each project in table task_project , we track time for each task in task_entries . I have created a method called elapsed to handle this.

So in my model TaskProject I have a relationship for tasks and for elapsed :

public function tasks()
{
    return $this->hasMany(TaskEntry::class, 'task_project_id');
}

public function elapsed()
{
    return $this->hasOne(TaskEntry::class, 'task_project_id')
        ->selectRaw('time_format(SUM(timediff(task_end_time, task_start_time)), "%H:%m:%s") AS hours')
        ->groupBy('task_entries.task_project_id');
}

And then in my controller I call it as follows:

$tasks = TaskProject::with('elapsed')->paginate(15);

But the relation for elapsed is a null value for each project row.

I would like to end up being able to access this value in my blade template as hh:mm:ss by using:

$task->elapsed->hours

Any help is appreciated!

Answer 1

Thats an interesting approach. I've faced the problem of how to get a list of aggregates from Eloquent before. This is the best I've been able to come up with.

class TaskEntry
{
    public static function addElapsedTo($tasks)
    {
        $ids = $tasks->pluck('id');
        $placeholders = trim(str_repeat('?,', count($ids)), ',');

        $times = DB::select('
            SELECT 
                task_project_id,
                TIME_FORMAT(
                    SUM(TIMEDIFF(task_end_time, task_start_time)),
                    "%H:%m:%s"
                ) AS hours
            FROM task_entries
            WHERE task_project_id IN ('.$placeholders.')
            GROUP BY task_project_id
        ', $ids);

        $times = collect($times)->groupBy('task_project_id');

        foreach ($tasks as $task)
        {
            $task->setAttribute('elapsed', $times[$task->task_project_id]['hours']);
        }
        return $tasks;
    }
}

Then you can use it like this.

$tasks = TaskProject::paginate(15);
$tasks = TaskEntry::addElapsedTo($tasks);

$task->elapsed contains the elapsed hours value.

This way you execute two database queries instead of one. But you still avoid executing a query for every result.

Methods like this have worked well for me. Though it feels a little kludgy. I would love to find a better way.