Count Documents Matching Multiple Array Criteria - spring

Question

Schema is:
{
"_id" : ObjectId("594b7e86f59ccd05bb8a90b5"),
"_class" : "com.notification.model.entity.Notification",
"notificationReferenceId" : "7917a5365ba246d1bb3664092c59032a",
"notificationReceivedAt" : ISODate("2017-06-22T08:23:34.382+0000"),
"sendTo" : [
{
"userReferenceId" : "check",
"mediumAndDestination" : [
{
"medium" : "API",
"status" : "UNREAD"
}
]
}
]
}
{
"_id" : ObjectId("594b8045f59ccd076dd86063"),
"_class" : "com.notification.model.entity.Notification",
"notificationReferenceId" : "6990329330294cbc950ef2b38f6d1a4f",
"notificationReceivedAt" : ISODate("2017-06-22T08:31:01.299+0000"),
"sendTo" : [
{
"userReferenceId" : "check",
"mediumAndDestination" : [
{
"medium" : "API",
"status" : "UNREAD"
}
]
}
]
}
{
"_id" : ObjectId("594b813ef59ccd076dd86064"),
"_class" : "com.notification.model.entity.Notification",
"notificationReferenceId" : "3c910cf5fcec42d6bfb78a9baa393efa",
"notificationReceivedAt" : ISODate("2017-06-22T08:35:10.474+0000"),
"sendTo" : [
{
"userReferenceId" : "check",
"mediumAndDestination" : [
{
"medium" : "API",
"status" : "UNREAD"
}
]
},
{
"userReferenceId" : "hello",
"mediumAndDestination" : [
{
"medium" : "API",
"status" : "READ"
}
]
}
]
}
I want to count a user notifications based on statusList which is a List. I used mongoOperations to make a query:
Query query = new Query();
query.addCriteria(Criteria.where("sendTo.userReferenceId").is(userReferenceId)
.andOperator(Criteria.where("sendTo.mediumAndDestination.status").in(statusList)));
long count = mongoOperations.count(query, Notification.class);
I realise I'm doing it wrong because I am getting count as 1 when I query for user with reference ID hello and statusList with single element as UNREAD.
How do I perform an aggregated query on array element?

Answer 1

The query needs $elemMatch in order to actually match "within" the array element that matches both criteria:
Query query = new Query(Criteria.where("sendTo")
.elemMatch(
Criteria.where("userReferenceId").is("hello")
.and("mediumAndDestination.status").is("UNREAD")
));
Which essentially serializes to:
{
"sendTo": {
"$elemMatch": {
"userReferenceId": "hello",
"mediumAndDestination.status": "UNREAD"
}
}
}
Note that in your question there is no such document, the only matching thing with "hello" actually has the "status" of "READ". If I supply those criteria instead:
{
"sendTo": {
"$elemMatch": {
"userReferenceId": "hello",
"mediumAndDestination.status": "READ"
}
}
}
Then I get the last document:
{
"_id" : ObjectId("594b813ef59ccd076dd86064"),
"_class" : "com.notification.model.entity.Notification",
"notificationReferenceId" : "3c910cf5fcec42d6bfb78a9baa393efa",
"notificationReceivedAt" : ISODate("2017-06-22T08:35:10.474Z"),
"sendTo" : [
{
"userReferenceId" : "check",
"mediumAndDestination" : [
{
"medium" : "API",
"status" : "UNREAD"
}
]
},
{
"userReferenceId" : "hello",
"mediumAndDestination" : [
{
"medium" : "API",
"status" : "READ"
}
]
}
]
}
But with "UNREAD" the count is actually 0 for this sample.