PHP：具有位置运算符的嵌入式文档数组上的MongoDB投影

Question

I want to retrieve a specific array from embedded document on matching base but either the output is displaying all arrays in that document not a specific one or displaying just the first array.... this is my code please have a look and answer this according to PHP.

$dept->findOne(['$and' => [
    ['_id' => 'd004'],
    ['dept_employees.from_date' => '1986-12-01'],
    ['dept_employees.to_date' => '9999-01-01']
                         ]
    ],
    ['projection' => ['dept_employees.$' => 1] ]);

this is the output

 MongoDB\\Model\\BSONDocument::__set_state(array( '_id' => 'd004', 'dept_employees' => MongoDB\\Model\\BSONArray::__set_state(array( 0 => MongoDB\\Model\\BSONDocument::__set_state(array( 'emp_id' => '10003', 'from_date' => '1995-12-03', 'to_date' => '9999-01-01', )), )), )) 

the document is like this have 247 sub-arrays

 MongoDB\\Model\\BSONDocument::__set_state(array( '_id' => 'd004', 'dept_employees' => MongoDB\\Model\\BSONArray::__set_state(array( 0 => MongoDB\\Model\\BSONDocument::__set_state(array( 'emp_id' => '10003', 'from_date' => '1995-12-03', 'to_date' => '9999-01-01', )), 1 => MongoDB\\Model\\BSONDocument::__set_state(array( 'emp_id' => '10004', 'from_date' => '1986-12-01', 'to_date' => '9999-01-01', )), 2 => MongoDB\\Model\\BSONDocument::__set_state(array( 'emp_id' => '10010', 'from_date' => '1996-11-24', 'to_date' => '2000-06-26', )), 

and i want only this

 MongoDB\\Model\\BSONDocument::__set_state(array( '_id' => 'd004', 'dept_employees' => MongoDB\\Model\\BSONArray::__set_state(array( 1 => MongoDB\\Model\\BSONDocument::__set_state(array( 'emp_id' => '10004', 'from_date' => '1986-12-01', 'to_date' => '9999-01-01', )), 

Dates are here only as strings, i am just matching strings. The shell is also displaying same results:

db.departments.find( {"dept_employees.from_date": '1986-12-01',    
"dept_employees.to_date": '9999-01-01'}, {"dept_employees.$":1} ).pretty()
{
        "_id" : "d004",
        "dept_employees" : [
                {
                        "emp_id" : "10003",
                        "from_date" : "1995-12-03",
                        "to_date" : "9999-01-01"
                }
        ]
}

Answer 1

According to MongoDB documentation :

The positional $ operator limits the contents of an from the query results to contain only the first element matching the query document.

and :

See the aggregation operator $filter to return an array with only those elements that match the specified condition.

https://docs.mongodb.com/manual/reference/operator/projection/positional/

https://docs.mongodb.com/manual/reference/operator/aggregation/filter/#exp._S_filter

Also, not exactly sure in your case, but if you are looking to match date ranges, maybe using '$gt' and '$lt' can help.