Laravel：根据 Eloquent 关系获取用户

Question

I have a User model which has an attribute type among other attributes. Type is used to identify parents and children .

Parent and children (students) have many-to-many relationship. Also students belong to one or many groups (model Group ).

User model

/**
 * Filter the scope of users to student type.
 *
 * @param $query
 */
public function scopeStudent($query){
    $query->where('type', '=', 'std');
}

/**
 * Filter the scope of users to parent type.
 *
 * @param $query
 */
public function scopeParent($query){
    $query->where('type', '=', 'prt');
}

/**
 * List of groups the user is associated with.
 *
 * @return \Illuminate\Database\Eloquent\Relations\BelongsToMany
 */
public function groups(){
    return $this->belongsToMany('\App\Group', 'group_user_assoc')
                ->withTimestamps();
}

/**
 * List of students associated with the user(parent).
 *
 * @return \Illuminate\Database\Eloquent\Relations\BelongsToMany
 */
public function children(){
    return $this->belongsToMany('\App\User', 'student_parent_assoc', 'parent_id', 'student_id')
                ->withPivot('relation');
}

/**
 * List of parents associated with the user(student).
 *
 * @return \Illuminate\Database\Eloquent\Relations\BelongsToMany
 */
public function parents(){
    return $this->BelongsToMany('\App\User', 'student_parent_assoc', 'student_id', 'parent_id')
                ->withPivot('relation');
}

The aforementioned relations are working correctly.

Below are my association tables.

student_parent_assoc
----------------------
+------------+------------------+------+-----+
| Field      | Type             | Null | Key |
+------------+------------------+------+-----+
| student_id | int(10) unsigned | NO   | PRI |
| parent_id  | int(10) unsigned | NO   | PRI |
| relation   | varchar(25)      | YES  |     |
+------------+------------------+------+-----+

group_user_assoc
----------------------
+------------+------------------+------+-----+
| Field      | Type             | Null | Key |
+------------+------------------+------+-----+
| group_id   | int(10) unsigned | NO   | MUL |
| user_id    | int(10) unsigned | NO   | MUL |
| created_at | timestamp        | NO   |     |
| updated_at | timestamp        | NO   |     |
+------------+------------------+------+-----+

I need to find students who do not belong to any group along with their parents. I have managed to find students like so

$students = User::student()
                ->whereDoesntHave('groups')
                ->get();

Question: Now I want to find parents of these students. But I am not able to build an eloquent query for the same. How do I do it?

Note: I could get collection of students from above query and run a foreach loop to get their parents like so

$parents = new Collection;
foreach($students as $student) {
    foreach($student->parents as $parent) {
        $parents->push($parent);
    }
}
$parents = $parents->unique();

But I need a Builder object and not a Collection as I am using Datatables server side processing with Yajra/datatables .

Answer 1

for loading parents relation you hae to use eager loading. 2 methods are with($relation) and load($relation) . Difference is just you get parents already with result objects or load them later.

So in your example to get parents you can use with('parents') or if you want to modify resulted set:

User::student()
->with(['parents' => function ($parentsQueryBuilder) {
    $parentsQueryBuilder->where('condition', 1)->whereIn('condition2', [1,2,3]);
}])
->whereDoesntHave('groups')
->get();

Then you will get your parents in a relationship aswell but performance will be high cause you will spend only one query to load parents to your objects. Then you can pluck if needed them in one collection like this:

$students->pluck('parents')->flatten()->unique();

Or example 2 - if you just need all parents related to selected students - almost the same what eager loading does:

$studentIds = $students->modeKeys();
User::parent()->whereHas('children', function ($query) use($studentIds) {
    $query->whereIn('id', $studentIds);
})->get();

UPDATED

For getting builder of parents try this:

/** BelongsToMany   <- relation query builder */    
$relation = with(new User)->query()->getRelation('parents');

$relation->addEagerConstraints($students->all());

This will create for you new instance of BelongsToMany relation and attach Constraints of whereIn($studentIds) to it. Then hitting ->get() on it you have to receive related $parents

Answer 2

Well, I managed to solve it like so

$students = User::student()
                ->with('parents')
                ->whereDoesntHave('groups')
                ->has('parents') //to get only those students having parents
                ->get();

$parent_ids = array();

// get ids of all parents
foreach ($students as $student) {
    foreach ($student->parents as $parent) {
        $parent_ids[] = $parent->user_id;
    }
}

// build the query
$users = User::parent()
             ->with('children')
             ->whereIn('user_id', $parent_ids);

I would still like it if someone could suggest a better and simple approach.