$lookup using multiple criteria mongodb java aggregation - mongodb

Question

Have 2 following collections:
user collection
{
userId:user1,
creationTimeStamp:2019-11-05T08:15:30
status:active
},
{
userId:user2,
creationTimeStamp:2019-10-05T08:15:30
status:active
}
document collection
{
userId:user1,
category:Development
published:true
},
{
userId:user2,
category:Development
published:false
}
I want to join these two collections and filter users such that documents which are of development category and are not published from active users between creationtimestamp
How can I write a mongodb java aggregation in order to get a result like this:
{
userId: user2,
status:active,
category:Development,
published:false
}

Answer 1

You could run below aggregation query on the document collection to get the expected result
[{$match: {
category:'development',
published: false
}}, {$lookup: {
from: 'user',
localField: 'userId',
foreignField: 'userId',
as: 'JoinedTable'
}}, {$unwind: {
path: '$JoinedTable'
}}, {$group: {
_id: '$_id',
userId: {
$first: '$userId'
},
status: {
$first: '$JoinedTable.status'
},
category: {
$first: '$category'
},
published: {
$first: '$published'
},
}}]
Explanation:
1. filter documents using match for criteria category: 'development' & published: false
2. join document collection with user collection with key userId
3. unwind the joined collection field to convert array to object
4. project the fields needed using groups.
Hope this helps!

Answer 2

You haven't mentioned about the duplicate of userId in User collection.
So the script is
[{
$match: {
category: "Development",
published: false
}
}, {
$lookup: {
from: 'user',
localField: 'userId',
foreignField: 'userId',
as: 'joinUser'
}
}, {
$unwind: {
path: "$joinUser",
preserveNullAndEmptyArrays: true
}
}, {
$match: {
"joinUser.status": "active"
}
}, {
$addFields: {
"status": "$joinUser.status"
}
}, {
$project: {
_id: 0,
userId: 1,
category: 1,
published: 1,
status: 1
}
}]
And the java code,
include these imports
import static org.springframework.data.mongodb.core.aggregation.Aggregation.match;
import static org.springframework.data.mongodb.core.aggregation.Aggregation.lookup;
import static org.springframework.data.mongodb.core.aggregation.Aggregation.unwind;
import static org.springframework.data.mongodb.core.aggregation.Aggregation.project;
method is,
public Object findAllwithVideos() {
Aggregation aggregation=Aggregation.newAggregation(
match(Criteria.where("category").is("Development").and("published").is(false)),
lookup("user","userId","userId","joinUser"),
unwind("joinUser",true),
new AggregationOperation(){
#Override
public Document toDocument(AggregationOperationContext aggregationOperationContext){
return new Document("$addFields",
new Document("status","$joinUser.status")
);
}
},
project("userId","category","published","status")
).withOptions(AggregationOptions.builder().allowDiskUse(Boolean.TRUE).build());
return mongoTemplate.aggregate(aggregation, mongoTemplate.getCollectionName(Document.class), Object.class);
}