Question

I have a list of embedded entities:

@Embedded
private List<EmbeddedEntity> embedded = new ArrayList<EmbeddedEntity>();

In this list, I want to search for any embedded entity which has a specific attribute (let’s call it foo), but not another one (bar). So foo should be non-null and bar null in Java / inexistant in MongoDB.

I tried the following code (I do have the UUID of the Entity containing the list):

Query<Entity> query = mongoDataStore.find(Entity.class).field("uuid").equal(uuid)
    .field("embedded.foo").exists()
    .field("embedded.bar").doesNotExist();

This works correctly if the list is empty or has a single entry (where foo has a value and bar does not yet exist). But as soon as any bar attribute has a value, the query returns the wrong result. So I’m looking for a query, which iterates through all the embedded entities and fires on any missing bar. Is that possible?

Example data:

// the query does not pick up the entity as it doesn't have a foo -
// that's what I want
{ uuid: "...", [ { embedded: } ] }

// the query picks up the entity as there is a foo but no bar -
// that's what I want
{ uuid: "...", [ { embedded: { foo: date } } ] }

// the query does not pick up the entity - that's not what I want
// as one foo has a value and its bar doesn't
{ uuid: "...", [ { embedded: { foo: date, bar: date } },
                 { embedded: { foo: date } }
               ] }

PS: I get the same result with .field("embedded.bar").hasThisOne(null).

PPS: Manually iterating through the list elements is not really an option, as I want to use the query for an update operation.

PPS: I think this is a bug in Morphia – see my answer below (https://stackoverflow.com/a/9705175/573153) for a workaround

Answer 1

I’ve found a workaround. While I don’t seem to be able to query on null, I can query for a specific value.

In my case, the bar field is a Date. So I can initialize the entity with private Date bar = new Date(0) – this is clearly an invalid date in my case, which is never used. So the query then looks like this:

Query<Entity> query = mongoDataStore
    .find(Entity.class)
    .field("uuid").equal(uuid)
    .field("embedded.foo").exists()
    .field("embedded.bar").hasThisOne(new Date(0));

And in case anyone needs it, here is the update operation (you need to disable the validation as .$. will otherwise raise an error):

UpdateOperations<Entity> update = mongoDataStore
    .createUpdateOperations(Entity.class)
    .disableValidation()
    .set("embedded.$.bar", new Date());

mongoDataStore.update(query, update);