Convert a String to Object (json) MongoDB shell

Question

I am trying to execute the below command

function(field) {

   //field = '{"'+field+'":{$exists:true}}'; Not working
   //field = tojson(field) Not working
   //field = {"events.concessionDetails":{$exists:true}}; Works if passed as input param


    print(field);
    var cur = db.cssCases.aggregate([

    {$match:{"events.eventType" : {$nin:["FAIL_SYSTEM_SERVICE_CALL"]}}},

    { $unwind: "$events" },

    {$match:field},

    {$group:{_id:{eventType:"$events.eventType"}}},

    { $limit : 100 }

    ])
}

if I pass the below value for the field it works fine.

var field1 = {"events.concessionDetails":{$exists:true}};

But I dont want to pass the '{$exists:true}' and just want to pass events.concessionDetails and form the full command, Below is some code which I would like to execute to accomplish this task.

I tried the following with no success,

tojson(field) tojsonObject(field) eval(field)

Is there any way that we can use to convert a input string to json query to use it in query.

The first line won't work cos you convert it into a string literal instead of a JS primative (a.k.a an Object), try something like (without testing this one bit) `var field = {""+field+"": {$exists: true}}` — Sammaye, Jul 09 '15 at 00:51
@Sammaye: The escape character is \ in Javascript, we tried it and we tried yours as well, its working. — Senthil Arumugam SP, Jul 09 '15 at 16:07

score 0 · Answer 1 · answered Jul 10 '15 at 16:00

Why don't you put the {$exists: true} part in your function code ?

Something like :

var field = "events.concessionDetails" // function argument

var match = {
    $match: {}
}
match.$match[field] = { exists: true }

Then use the match variable when you call the aggregate method.

Convert a String to Object (json) MongoDB shell

1 Answers1