CakePHP 3.x - hasMany 通过关联 - 查找

Question

假设我的设置与 CookBook 中的设置完全相同： http://book.cakephp.org/3.0/en/orm/associations.html

class StudentsTable extends Table
{
    public function initialize(array $config)
    {
        $this->belongsToMany('Courses', [
            'through' => 'CourseMemberships',
        ]);
    }
}

class CoursesTable extends Table
{
    public function initialize(array $config)
    {
        $this->belongsToMany('Students', [
            'through' => 'CourseMemberships',
        ]);
    }
}

class CoursesMembershipsTable extends Table
{
    public function initialize(array $config)
    {
        $this->belongsTo('Students');
        $this->belongsTo('Courses');
    }
}

Student BelongsToMany Course
Course BelongsToMany Student

id | student_id | course_id | days_attended | grade

我应该如何构造查询来查找给定学生的课程，他的成绩 ==“A”？

$query = $this->Courses->find('all')
    ->contain(['CourseMemberships'])
    ->where(['CourseMemberships.student_id' => $student['id'], 'CourseMemberships.grade' => 'A']);

这行不通。应该怎么写？

Answer 1

通常您会使用matching，但 ORM 似乎不支持在连接表“关联”上进行匹配，因为此时它们不是“真正的”关联（您可能想要suggest that as an enhancement），稍后会添加它们。

matching() 解决方法

有效的是在外部查询上使用matching() 和where()，即

$query = $this->Courses
    ->find('all')

     // contain needs to use `Students` instead (the `CourseMemberships`
     // data can be found in the `_joinData` property of the tag),
     // or dropped alltogether in case you don't actually need that
     // data in your results
    ->contain(['Students'])

     // this will do the magic
    ->matching('Students')

    ->where([
        'CourseMemberships.student_id' => $student['id'],
        'CourseMemberships.grade' => 'A'
    ]);

这将使用CourseMemberships 别名加入students 表以及courses_students 连接表，例如

INNER JOIN
    students Students ON 1 = 1
INNER JOIN
    courses_students CourseMemberships ON (
        Courses.id = (CourseMemberships.course_id)
        AND Students.id = (CourseMemberships.student_id)
    )

因此可以应用条件。感觉这不是一个很好的解决方法。

使用额外的关联（可能是更好的方法）

另一种选择是添加另一个显式关联（就像提到的@AtaboyJosef），即连接表的hasMany 关联（这将在稍后自动完成，但如前所述，它也是matching() 迟到了）。

请注意，这需要将连接表命名为course_memberships！

class CoursesTable extends Table
{
    public function initialize(array $config)
    {
        $this->belongsToMany('Students', [
            'joinTable' => 'course_memberships',
            'through' => 'CourseMemberships',
        ]);

        $this->hasMany('CourseMemberships', [
            'foreignKey' => 'course_id'
        ]);
    }
}

这样您就可以在CourseMemberships 关联上使用匹配

$query = $this->Courses
    ->find('all')
    // with this solution you can also use contain for `CourseMemberships`
    ->contain(['CourseMemberships'])
    ->matching('CourseMemberships', function(\Cake\ORM\Query $query) use ($student) {
        return $query->where([
            'CourseMemberships.student_id' => $student['id'],
            'CourseMemberships.grade' => 'A'
        ]);
    });

应该创建一个类似的查询

INNER JOIN course_memberships CourseMemberships ON (
    CourseMemberships.student_id = 1 
    AND CourseMemberships.grade = 'A' 
    AND Course.id = (CourseMemberships.course_id)
)

这可能会更有效，因为它需要更少的选择。

Answer 2

through 允许您提供要在连接表上使用的表实例的名称或实例本身。这使得自定义连接表键成为可能，并允许您自定义数据透视表的行为。

使用数组语法定义更具体的关系：

class StudentsTable extends Table
{

    public function initialize(array $config)
    {
        $this->belongsToMany('Courses', [
            'joinTable' => 'courses',
            'through' => 'CourseMemberships',
        ]);
    }
}

class CoursesTable extends Table
{

    public function initialize(array $config)
    {
        $this->belongsToMany('Students', [
            'joinTable' => 'students',
            'through' => 'CourseMemberships',
        ]);
    }
}

class CoursesMembershipsTable extends Table
{

    public function initialize(array $config)
    {
        $this->belongsTo('Students', [
            'foreignKey' => 'student_id',
            'joinType' => 'INNER',        // OR specify the type 
        ]);
        $this->belongsTo('Courses', [
            'foreignKey' => 'course_id',
            'joinType' => 'INNER',
        ]);
    }
}

确保您有表 courses、students 和 course_memberships。

现在运行代码：

$query = $this->Courses->find('all')
    ->contain(['CourseMemberships'])
    ->where(['CourseMemberships.student_id' => $student['id'], 'CourseMemberships.grade' => 'A']);

好吧，如果你真的需要与HasMany Associations 相关的东西，我很害怕。