我如何从3张桌子中获得价值？

Question

表：项目 enter image description here

表：projects_departments enter image description here 表格：部门enter image description here

这是模型项目

public function projects_departments() {
    return $this->hasMany(Project_department::class); 
}

这是Model Project_department

public function projects()
{
    return $this->belongsTo(Project::class);
}

public function departments()
{
    return $this->belongsTo(Department::class);
}

这是模特部

public function projects()
{
    return $this->hasMany(Project::class);
}

public function projects_departments() {
    return $this->hasMany(Project_department::class); 
}

这是我的刀刃

project->departments->department_name

这是我的错误 SQLSTATE [42S22]：找不到列：1054“ where子句”中的未知列“ projects_departments.project_id”（SQL：从projects_departments中选择*，其中projects_departments。project_id = 48，{{ 1}}。projects_departments不为空）

Answer 1

$project = DB::table('projects')
        ->select(*)
        ->join('Department', 'projects_departments.department_id', '=', 'Department.id')
        ->join('projects_departments', 'projects_departments.project_id', '=', 'projects.id')

        ->get();

让我们尝试一下