Mongo db aggregate convert array to string

Question

have a collection with data


date_new:Array

Using mongodb aggregation how to convert into string like this, if there is a empty string convert it into " "



date_new:Array
    0: " "

@theUnknown : Please check the answer below, I've few question, date_new : [0:'', 1:''], So it has to be an array of objects date_new : [ {0:' '},{ 1:' '} ] or with object & it's elements like below result. Also what do you mean by if there is a empty string convert it into " " ?? We're converting array how come there will be empty string ? Do you mean an element in date_new as empty string ? — whoami - fakeFaceTrueSoul
– whoami - fakeFaceTrueSoul, Commented Jan 14, 2020 at 21:24

whoami - fakeFaceTrueSoul · Accepted Answer · 2020-01-14 21:16:52Z

Please try this :

db.yourCollectionName.aggregate([{
    $addFields:
    {
        date_new: {
            $arrayToObject:
            {
                $map:
                {
                    input: "$date_new",
                    as: "each",
                    in: [{ $toString: { $indexOfArray: ["$date_new", '$$each'] } }, '$$each']
                }
            }
        }
    }
}])

Collection Data :

/* 1 */
{
    "_id" : ObjectId("5e1e2a74d3c98f2a7100fd44"),
    "date_new" : [ 
        "abc", 
        "def", 
        ""
    ]
}

/* 2 */
{
    "_id" : ObjectId("5e1e2f25d3c98f2a7100fd45"),
    "date_new" : []
}

Result :

/* 1 */
{
    "_id" : ObjectId("5e1e2a74d3c98f2a7100fd44"),
    "date_new" : {
        "0" : "abc",
        "1" : "def",
        "2" : ""
    }
}

/* 2 */
{
    "_id" : ObjectId("5e1e2f25d3c98f2a7100fd45"),
    "date_new" : {}
}

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