Spring mongo slice array in embedded document - mongodb

Question

The slice method in aggreation for array within an embedded document is not working for me using spring mongo template.
Example:
Invoice collection:
{
"reference_number": "aaa111",
"historical_data": {
"year": 2010,
"data": [
{
"item_name": "Apple",
"price": 50
},
{
"item_name": "Book",
"price": 200
}
]
}
}
Using mongoTemplate I would like to get only the historical data in slices.
For the arrays which needs to be sliced that appear directly under the root I had found a solution using aggregation
Refer : Spring mongo repository slice
Applying a similar query for array in an embedded document returns an empty list even if there is data.
The query that I was trying was :
TypedAggregation<Invoice> agg = newAggregation(Invoice.class,
match(where("reference_number").is(referenceNumber)),
project.andExpression("historicalData.data").slice(limit, offset));
AggregationResults<Invoice> result = mongoTemplate.aggregate(agg, Invoice.class, Invoice.class);
But this returns an empty list of data.
Is there any other alternative way to get the sliced result for arrays within an embedded document?
Invoice.java
#Data
#Document(collection = "invoice")
public class Invoice {
#Id
private String id;
#NotEmpty
#Indexed(unique = true)
#Field("reference_number")
private String referenceNumber = UUID.randomUUID().toString();
#Valid
#Field("historical_data")
private HistoricalData historicalData = new HistoricalData();
}
HistoricalData:
#Data
public class HistoricalData {
#NotEmpty
#Field("year")
private Intger year;
#Valid
#NotNull
#Field("data")
private List<InvoiceData> data = new LinkedList<>();
}
Note : I have also tried :
TypedAggregation<Invoice> agg = newAggregation(Invoice.class,
match(where("reference_number").is(referenceNumber)),
project.andExpression("historical_data.data").slice(limit, offset));
AggregationResults<Invoice> result = mongoTemplate.aggregate(agg, Invoice.class, Invoice.class);
But this gave me a PropertyPathException.
Thanks in advance!!

Answer 1

After a weeks struggle I have figured out a solution for this:
ProjectionOperation project = project().and("historicalRevisionData.data").slice(limit, offset).as("historical_revision_data.data")
.andInclude("id")
.and("referenceNumber").as("reference_number");
TypedAggregation<Invoice> agg = newAggregation(Invoice.class,
match(where("reference_number").is(referenceNumber)),
project);
AggregationResults<TaxInvoice> aggregate = mongoTemplate.aggregate(agg, Invoice.class, Invoice.class);
Hoping that this would help someone else too.