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以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

through 允许您提供要在联接 table 上使用的 Table 实例的名称，或者实例本身。这使得自定义连接 table 键成为可能，并允许您自定义枢轴 table.

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',
        ]);
    }
}

请确保您有 tables 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 有关的东西，我很担心。

Answer 2

通常您会使用 matching, but the ORM doesn't seem to support matching on join table "associations", as they are not "real" associations at that point (you may want to suggest that as an enhancement)，稍后会添加它们。

`matching()` 解决方法

有效的方法是在外部查询中使用 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 table 以及 courses_students 加入 table，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)
    )

等条件可以适用。这感觉像是一个不太好的解决方法。

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@AtaboyJosef 提到的那样），即 hasMany 连接的关联 table（这将在稍后自动完成，但正如已经提到的，matching()).

为时已晚

请注意，这需要将联接 table 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'
        ]);
    }
}

这样你就可以在 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)
)

这可能会更有效一些，因为它需要更少的选择。

CakePHP 3.x - hasMany 通过关联 - 查找

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CakePHP 3.x - hasMany through association - find

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