Apply $elemMatch to multiple arrays - mongodb

Question

The result of my query is:
{
"_id" : ObjectId("5b5e680bca55f2885cb3c864"),
"barcelona" : [
{
"date" : ISODate("2018-07-01T00:00:00.000+0000"),
"name" : "david",
"age" : 17.0
}
]
}
My query looks like this:
db.test8.find({ line: '2' },{ barcelona: { $elemMatch: {
date :
{
"$gte" : ISODate("2018-07-01T00:00:00Z"),
"$lt" : ISODate("2018-07-02T00:00:00Z")
}
}}});
The dataset looks like this in the mongodb. It has three arrays: barcelona, paris, and london. I will answer any questions you may have.
{
"_id" : ObjectId("5b5e680bca55f2885cb3c864"),
"piwikID" : "2",
"barcelona" : [
{
"date" : ISODate("2018-07-01T00:00:00.000+0000"),
"name" : "david",
"age" : 11.0
},
{
"date" : ISODate("2018-07-02T00:00:00.000+0000"),
"name" : "damo",
"age" : 16.0
},
{
"date" : ISODate("2018-07-03T00:00:00.000+0000"),
"name" : "dani",
"age" : 12.0
}
],
"paris" : [
{
"date" : ISODate("2018-07-01T00:00:00.000+0000"),
"name" : "david",
"age" : 17.0
},
{
"date" : ISODate("2018-07-02T00:00:00.000+0000"),
"name" : "damo",
"age" : 10.0
},
{
"date" : ISODate("2018-07-03T00:00:00.000+0000"),
"name" : "danp",
"age" : 13.0
}
],
"london" : [
{
"date" : ISODate("2018-07-01T00:00:00.000+0000"),
"name" : "dan",
"age" : 11.0
},
{
"date" : ISODate("2018-07-02T00:00:00.000+0000"),
"name" : "donner",
"age" : 12.0
},
{
"date" : ISODate("2018-07-03T00:00:00.000+0000"),
"name" : "dangus",
"age" : 14.0
}
]
};
There are other cities paris, london, etc. which are arrays and should display in my result.
How can I modify my query to show them in my result as well?

Answer 1

You want to use $elemMatch for multiple arrays first, you need to build the dynamic query.
Suppose you know the city names before you queried the DB you can build a query like this.
var cities = ['barcelona', 'paris', 'london'];
var query = {
"$or": []
};
for (let i = 0; i < cities.length; i++) {
let queryObj = {};
queryObj[cities[i]] = {
"$elemMatch": {
date:
{
"$gte": ISODate("2018-07-01T00:00:00Z"),
"$lt": ISODate("2018-07-02T00:00:00Z")
}
}
};
query["$or"].push(queryObj);
};
Your query like this :
{
"$or":
[{ "barcelona": { "$elemMatch": { "date": { "$gte": ISODate("2018-07-01T00:00:00Z"), "$lt": ISODate("2018-07-02T00:00:00Z") } } } },
{ "paris": { "$elemMatch": { "date": { "$gte": ISODate("2018-07-01T00:00:00Z"), "$lt": ISODate("2018-07-02T00:00:00Z") } } } },
{ "london": { "$elemMatch": { "date": { "$gte": ISODate("2018-07-01T00:00:00Z"), "$lt": ISODate("2018-07-02T00:00:00Z") } } } }]
}
db.col.find(query);