$concat mongo not working

Question

Using $project operator and want to concatenate two fields result and one string to them.

  'check_concat'=>array('$concat'=>'$pickup_delivery_date_and_time_to','cheema'),

giving output as an exception

127.0.0.1:27017: exception: this object is already an operator expression, and can't be used as a document expression (at '0')

This may help you with the exact notations to used.https://docs.mongodb.com/manual/reference/operator/aggregation/project/ — Dileephell, Jul 07 '16 at 11:45

score 0 · Answer 1 · edited May 23 '17 at 12:24

0

You should use double quotes:

'check_concat' => array("$concat"=>"$pickup_delivery_date_and_time_to",'cheema'),

What is the difference between single-quoted and double-quoted strings in PHP?

edited May 23 '17 at 12:24

Community

1
1

answered Jul 07 '16 at 11:48

Maksim I. Kuzmin

1,170
7
16

score 0 · Answer 2 · answered Jul 07 '16 at 13:18

The correct syntax follows, for example:

db.collection.aggregate([
    { 
        "$project": { 
            "check_concat": { 
                "$concat": ["$pickup_delivery_date_and_time_to", "cheema"] 
            } 
        } 
    }
])

in PHP, this translate to

<?php
$m = new MongoClient("localhost");
$c = $m->selectDB("test")->selectCollection("collection");
$ops = array(
    array(
        "$project" => array(
            "check_concat" => array(                
                "$concat" => array("$pickup_delivery_date_and_time_to", "cheema")
            )
        )
    )
);
$results = $c->aggregate($ops);
var_dump($results);
?>

Thanks @chridam Its working now according to your example .Cheers Thanks a lot. — Pankaj Cheema, Jul 08 '16 at 05:23

$concat mongo not working

2 Answers2