Consider the following document in the collection named 'CityAssociation'
{
"_id" : "MY_ID",
"ThisCityID" : "001",
"CityIDs" : [{
"CityID" : "001",
"CityName" : "Bangalore"
}, {
"CityID" : "002",
"CityName" : "Mysore"
}],
"CityUserDetails": {
"User" : "ABCD"
}
}
Now I have User
value ie in above case I have value ABCD
and want to find it with only city where the first level's field ThisCityID
matches to the embedded array documnet's field CityID
. Finally I need to project as follows (for the above case):
{
'UserName': 'ABCD',
'HomeTown':'Bangalore'
}
In Node.js + MongoDB native drive, I wrote a aggregation query as follows which is not working as expected.
collection.aggregate([
{ $match: { 'CityUserDetails.User': 'ABCD', 'CityIDs': { $elemMatch: { CityID: ThisCityID}}} },
{ $unwind: "$CityIDs" },
{ $group: {
_id: '$_id',
CityUserDetails: { $first: "$CityUserDetails" },
CityIDs: { $first: "$CityIDs" }
}
},
{ $project: {
_id: 0,
"UserName": "$CityUserDetails.User",
"HomeTown": "$CityIDs.CityName"
}
}
], function (err, doc) {
if (err) return console.error(err);
console.dir(doc);
}
);
Can anyone tell me how this can be done with query.
Note: On MongoDB schema we don't have control to change it.
You can use the $eq
operator to check if the first level's field ThisCityID matches embedded array document's field CityID.
db.city.aggregate([
{ $match : { "CityUserDetails.User" : "ABCD" }},
{ $unwind : "$CityIDs" },
{ $project : {
matches : { $eq: ["$CityIDs.CityID","$ThisCityID"]},
UserName : "$CityUserDetails.User",
HomeTown : "$CityIDs.CityName"
}},
{ $match : { matches : true }},
{ $project : {
_id : 0,
UserName : 1,
HomeTown : 1
}},
])
And the result is:
{
"result" : [
{
"UserName" : "ABCD",
"HomeTown" : "Bangalore"
}
],
"ok" : 1
}
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