我正在对employees表进行聚合,以通过投影来获取一些旅馆详细信息,例如
$query = ['_id' => new MongoDB\BSON\ObjectID($this->EmployeeId)];
$pipeline = array(
['$match' => $query],
[ '$addFields'=> [
'assigned_master_keys'=> [
'$cond'=> [
'if'=> [
'$ne'=> [ [ '$type'=> '$assigned_master_keys' ], 'array' ]
],
'then'=> [],
'else'=> '$assigned_master_keys'
]
]
]],
['$unwind'=> '$assigned_master_keys'],
['$lookup' => [
'from' => 'HostelTbl',
'let' => [ 'hostelid' => '$assigned_master_keys.hostel_id' ],
'pipeline' => [
['$match' => [ '$expr'=> [ '$eq' => [ '$_id', '$$hostelid' ]]]],
['$project' => [ 'Name'=> 1, 'MasterKeyDetails' => 1, '_id'=> 1]]
],
'as' => 'assigned_master_keys.hostel_id'
]],
);
$this->collection = $this->db->EmployeesTbl;
$cursor = $this->collection->aggregate($pipeline);
上面的代码对于那些名称为“ assigned_master_keys”的嵌入式文档的员工有效,但对于那些不存在“ assigned_master_keys”的员工则适用。分页符。如果我从上述代码中删除了unwind,该页面不会中断,但也不会获取旅馆数据。
请帮助!!!
答案 0 :(得分:1)
将$unwind
与preserveNullAndEmptyArrays
选项一起使用
['$unwind'=> ['path' => '$assigned_master_keys', 'preserveNullAndEmptyArrays' => true ]]