Cannot create an array of nested object using a project operation - mongodb

Question

I'm forced to use the aggregation framework and the project operation of Spring Data MongoDb.
What I'd like to do is creating an array of object as a result of a project operation.
For example, considering this intermediate aggregation result:
[
{
"content": {
"processes": [
{
"id": "101a",
"title": "delivery"
},
{
"id": "101b",
"title": "feedback"
}
]
}
}
]
What I want to obtain is this:
[
{
"results":
{
"titles": [
{
"id": "101a",
"value": "delivery"
},
{
"id": "101b",
"value": "feedback"
}
]
}
}
]
This was just an example, I don't want to simply "rename" some fields.
What I want is the possibility to create an array of objects.
If I try something like this:
projectionOperation
.and("$content.processes.id").as("results.titles.id")
.and("$content.processes.title").as("results.titles.value");
I obtain this:
[
{
"results":
{
"titles": {
"id": ["101a", "101b"]
"value": ["delivery", "feedback"]
}
}
}
}
]
With this projection the array is created, but not "in the proper position".
However, If I use the nested operator, I haven't figure out a way to specify that I want to create an array instead of an object.
With this projection:
projectionOperation.and("results.titles")
.nested(
bind("id", "process.id")
.and("value", "process.title")
);
I can create a proper nested object but not into an array:
"results.titles": {
"id": "101b",
"value": "feedback"
}

Answer 1

You can try below aggregation code.
ProjectionOperation po = Aggregation.project().and(
VariableOperators.mapItemsOf("content.processes").as("rt")
.andApply(
new AggregationExpression() {
#Override
public Document toDocument(AggregationOperationContext aggregationOperationContext) {
return new Document("id", "$$rt.id").append("value", "$$rt.title");
}
}
)
).as("result");