Sort by in mongodb field contains an array

Question

I have a collection in which I store data in below format I want to apply sort by in below collection.

{
"job_count" : [ 
        ObjectId("58eb607531f78831a8894a3e"),
        ObjectId("58eb607531f78831a8894a3e"),
        ObjectId("58eb607531f78831a8894a3e")
    ]
},
{
"job_count" : [ 
        ObjectId("58eb607531f78831a8894a3e")
    ]
},
{
"job_count" : [ 
        ObjectId("58eb607531f78831a8894a3e"),
        ObjectId("58eb607531f78831a8894a3e")
    ]
}

i want data to be like as below

{
    "job_count" : [ 
            ObjectId("58eb607531f78831a8894a3e"),
            ObjectId("58eb607531f78831a8894a3e"),
            ObjectId("58eb607531f78831a8894a3e")
        ]
    },
    {
    "job_count" : [ 
            ObjectId("58eb607531f78831a8894a3e"),
            ObjectId("58eb607531f78831a8894a3e")
        ]
    },
    {
    "job_count" : [ 
            ObjectId("58eb607531f78831a8894a3e")
        ]
    }

my complete query is

Jobs.aggregate(
            {"$match"  : $condArray},
            {"$unwind" : { path: "$mytradesmen.hired", preserveNullAndEmptyArrays: true}},
            {"$lookup" : {
                        "from":"users",
                        "localField":"mytradesmen.hired",
                        "foreignField":"_id",
                        "as": "user_details"
                    }
            },
            {"$unwind": { path: "$user_details", preserveNullAndEmptyArrays: true}},

            { "$sort" : {"job_count":-1}})

Can anyone help me figure out the query i should modify to get the expected result, please let me know in case of any further detail required i will edit my question accordingly

chridam · Accepted Answer · 2017-04-19 09:46:29Z

2

Use the $size operator to create an extra field that holds the count of the elements in the array and then $sort on that field:

Jobs.aggregate([
    {
        "$project": {
            "count": { "$size": "$job_count" },
            "job_count": 1
        }
    },
    { "$sort" : { "count": -1 } }
])

answered Apr 19, 2017 at 9:46

chridam

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2 Comments

Mukesh Over a year ago

what if i want this to be conditional actually by using project i will have to mention all the field i need to display which will be quiet time taking is there any way to make this condition optional

chridam Over a year ago

There is a better way if you have MongoDB version 3.4 and greater which has the $addFields operator, equivalent to a $project stage that explicitly specifies all existing fields in the input documents and adds the new fields.

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