Morphia query to filter and fetch an embedded list element - mongodb

Question

I am new to NoSQL and morphia. I am using Morphia to query MongoDB.
I have a sample collection as below:
[
{
"serviceId": "id1",
"serviceName": "ding",
"serviceVersion": "1.0",
"files": [
{
"fileName": "b.html",
"fileContents": "contentsA"
},
{
"fileName": "b.html",
"fileContents": "contentsB"
}
]
},
{
"serviceId": "id2",
"serviceName": "ding",
"serviceVersion": "2.0",
"files": [
{
"fileName": "b.html",
"fileContents": "contentsA"
},
{
"fileName": "b.html",
"fileContents": "contentsB"
}
]
}
]
I would like to fetch an element in "files" List , given service name, service version and filename., using Morphia.
I was able to get what I want using the query below:
db.ApiDoc.find({ serviceName: "ding", serviceVersion: "2.0"}, { files: { $elemMatch: { fileName: "b.html" } } }).sort({ "_id": 1}).skip(0).limit(30);
What I tried so far :
I tried using "elemmatch" api that morphia has, but no luck.
query = ...createQuery(
Result.class);
query.and(query.criteria("serviceName").equal("ding"),
query.criteria("serviceVersion").equal(
"2.0"));
query.filter("files elem",BasicDBObjectBuilder.start("fileName", "a.html").get());
I seem to get the entire Result collection with all the files. I would like to get only the matched files(by filename).
can some one help me how I can get this to work?
Thanks
rajesh

Answer 1

I don't believe it's possible to get just the matching sub element. You can request just to have the 'files' array returned but all elements will be included in the result set and you will have to refilter in your code.
The other option is to make Files a collection of its own with a serviceId field and then you'll have more power to load only certain files.

Answer 2

It's possible to do that.
the filter doesn't really work like projection.
try this :
datastore.createQuery(Result.class)
.field("serviceName").equal("dong")
.field("serviceVersion").equal("2.0")
.field("files.filename").equal("a.html")
.project("files.$.filename", true);