爱因诗贤 ·前面小节介绍了如何在课程列表中使用一对一模型关联出教师信息，本小节介绍如何在学生课程关联列表中一对多关联出学生选课信息，一对多模型关联主要针对的是查询两个表有一对多的关系，而连表查询就可能带来性能问题， ThinkPHP中提供了 with()方法用于这种连表查询的预加载，在一对多模型关联的时候，框架底层会用过主驱动表的 id 集去另外一张表中 IN 查询一次获取全部数据并且能自动对应，这样的操作就减少了开发者书写很多循环和处理数据的代码了。
这里为了演示方便，需要向之前新建好的 学生表(student)、学生课程关联表(student_course) 添加数据，添加学生表数据的 SQL 如下：
如下图所示：
添加学生课程关联表数据 SQL 语句如下：
如下图所示：
这里复用上小节的控制器，只需要定义一个学生课表关列表的路由：
//学生课程表关联列表接口 Route::get('course-students','app\controller\Study\CourseController@courseStudnetList');代码块预览 复制
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如下图所示：
/** * 学生课表信息关联表 * @return \think\response\Json */ public function courseStudnetList(){ //每页条数 $size = (int)$this->request->param('size', 15); $courseStudents = StudentModel::order('created_at DESC') ->with('course_students') ->paginate($size); return json($courseStudents); }代码块预览 复制
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如下图所示：
在 StudentModel 中可以定义 courseStudents 方法：
/** * 一对多模型关联 * @return \think\model\relation\HasMany */ public function courseStudents(){ return $this->hasMany(StudentCourseModel::class,"student_id","id"); }代码块预览 复制
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如下图所示：
下面使用 postman 请求接口数据如下：
{ "total": 14, "per_page": 10, "current_page": 1, "last_page": 2, "data": [ { "id": 1, "name": "赵雷", "age": 24, "id_number": "42011720100506XXXX", "created_at": 1603617951, "update_at": 0, "status": 1, "course_students": [ { "id": 1, "student_id": 1, "course_id": 1, "created_at": 1603617951 }, { "id": 2, "student_id": 1, "course_id": 2, "created_at": 1603617951 }, { "id": 3, "student_id": 1, "course_id": 2, "created_at": 1603617951 } ], "created_at_text": "2020-10-25 17:25" }, { "id": 2, "name": "孙空", "age": 23, "id_number": "42011720110606XXXX", "created_at": 1603617951, "update_at": 0, "status": 1, "course_students": [ { "id": 4, "student_id": 2, "course_id": 3, "created_at": 1603617951 }, { "id": 5, "student_id": 2, "course_id": 4, "created_at": 1603617951 }, { "id": 6, "student_id": 2, "course_id": 6, "created_at": 1603617951 } ], "created_at_text": "2020-10-25 17:25" }, { "id": 3, "name": "钱学", "age": 18, "id_number": "42011720120306XXXX", "created_at": 1603617951, "update_at": 0, "status": 1, "course_students": [ { "id": 7, "student_id": 3, "course_id": 4, "created_at": 1603617951 }, { "id": 8, "student_id": 3, "course_id": 1, "created_at": 1603617951 } ], "created_at_text": "2020-10-25 17:25" }, { "id": 4, "name": "王五", "age": 25, "id_number": "42011720030506XXXX", "created_at": 1603617951, "update_at": 0, "status": 1, "course_students": [ { "id": 9, "student_id": 4, "course_id": 1, "created_at": 1603617951 }, { "id": 10, "student_id": 4, "course_id": 3, "created_at": 1603617951 } ], "created_at_text": "2020-10-25 17:25" }, { "id": 5, "name": "张红", "age": 19, "id_number": "42011720050506XXXX", "created_at": 1603617951, "update_at": 0, "status": 1, "course_students": [ { "id": 11, "student_id": 5, "course_id": 5, "created_at": 1603617951 }, { "id": 12, "student_id": 5, "course_id": 6, "created_at": 1603617951 } ], "created_at_text": "2020-10-25 17:25" }, { "id": 6, "name": "吴晓明", "age": 21, "id_number": "42011720040506XXXX", "created_at": 1603617951, "update_at": 0, "status": 1, "course_students": [ { "id": 13, "student_id": 6, "course_id": 4, "created_at": 1603617951 }, { "id": 14, "student_id": 6, "course_id": 2, "created_at": 1603617951 } ], "created_at_text": "2020-10-25 17:25" }, { "id": 7, "name": "李珍", "age": 25, "id_number": "42011720060206XXXX", "created_at": 1603617951, "update_at": 0, "status": 1, "course_students": [ { "id": 15, "student_id": 7, "course_id": 3, "created_at": 1603617951 }, { "id": 16, "student_id": 7, "course_id": 4, "created_at": 1603617951 } ], "created_at_text": "2020-10-25 17:25" }, { "id": 8, "name": "猪刚", "age": 22, "id_number": "42011720070806XXXX", "created_at": 1603617951, "update_at": 0, "status": 1, "course_students": [], "created_at_text": "2020-10-25 17:25" }, { "id": 9, "name": "李亮", "age": 26, "id_number": "42011720080906XXXX", "created_at": 1603617951, "update_at": 0, "status": 1, "course_students": [], "created_at_text": "2020-10-25 17:25" }, { "id": 10, "name": "周康", "age": 28, "id_number": "42011720000706XXXX", "created_at": 1603617951, "update_at": 0, "status": 1, "course_students": [], "created_at_text": "2020-10-25 17:25" } ] }代码块预览 复制
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如下图所示：
本小节主要介绍了一对多模型关联，其中使用 with 预加载底层实现是 IN 查询一次性查出来的，所以无需担心存在循环查询的问题，另外如需要在上述结果中继续关联出课程信息可以如下使用 with 闭包查询：
/** * 学生课表信息关联表 * @return \think\response\Json */ public function courseStudnetList(){ //每页条数 $size = (int)$this->request->param('size', 15); $courseStudents = StudentModel::order('created_at DESC') ->with(['course_students' => function($query){ $query->with('course'); }]) ->paginate($size); return json($courseStudents); }代码块预览 复制
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其中需要在 CourseStudentModel 模型中新建 course 一对一关联课程信息。
Tips： 代码仓库：https://gitee.com/love-for-poetry/tp6
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