how to convert epoch time stored in nested field to date mongodb

Question

I have a nested field msgs.crtDtTm inside a mongodb which has epoch date ( 1554120000 )stored as string. I need to convert msgs.crtDtTm to Date format to apply $gte (which is not working in String format).

cond: { $gte: [ "$msg.crtDtTm", "1554120000" ] }

I tried this but greater than operation not performed. It is returning all the nested elements without filtering.

Answer 1

You can convert string to date by this command :

new Date("1554120000")

Like this :

db.YourCollection.find({"created_at" : { $gte : new Date("1554120000") }});

in your example :

cond: {$msg.crtDtTm : { $gte:  new Date("1554120000") }}

Let me know the result please .

This link is also useful

Answer 2

Once your time april 1,2019 being converted into ms and then to type of string in your code, it would be easy that way(as converting one element vs n values in DB - altogether it might be easy for that format to be converted into ms in code), then use this query to retrieve elements that match your criteria :

db.yourCollection.aggregate([
    {$match: {'msgs.crtDtTm': {$gt: '1554120000'}}},
    {$addFields: {
        msgs: {$filter: {
            input: '$msgs',
            as: 'msg',
            cond: {$gt: ['$$msg.crtDtTm', '1554120000']}
        }}
    }}
])

You could achieve similar using $unwind on msgs & then $match finally $group or $match to start with, which ever is feasible you can go ahead. Something like this :

db.yourCollection.aggregate([{
    $match: {
        'msgs.crtDtTm': { $gt: '1554120000' }
    }
},
{ $unwind: "$msgs" },
{
    $match: {
        'msgs.crtDtTm': { $gt: '1554120000' }
    }
}, { $group: { _id: '$_id', msgs: { $push: '$msgs' }, docs: { $first: '$$ROOT' } } }, { $addFields: { 'docs.msgs': '$msgs' } }, { $replaceRoot: { newRoot: '$docs' } }])

Lastly, It would be a better idea if you can store the same format which will be used to query.