Remove an entry from array using MongoDB-Java driver

Question

I have JSON like :

{ 
    "_id" : "1",
    "_class" : "com.model.Test",
    "itemList" : [
        {
            "itemID" : "1",
            "itemName" : "Foo",
            "resources" : [ 
                { 
                    "resourceID" : "1",
                    "resourceName" : "Foo Test1"
                 }, {
                    "resourceID" : "2",
                    "resourceName" : "Foo Test2"
                 }
             ]
        }
    ]
}

I need to be able to remove one of records of itemList. I have done the following:

public void removeItemByID(String docID, String itemID) throws Exception {
    MongoOperations mongoOperations = mongoConfiguration.getMongoTemplate();
    Query query = new   Query(where("_id").is(docID).and("itemList.itemID").is(itemID));
    mongoOperations.remove(query, Item.class);

}

This approach doesn't work. However when I have used the BasicDBObject with $pull approach it works fine ! What's the difference among these approaches !

Answer 1

If you want to remove an array generally I use the following:

BasicDBObject match = new BasicDBObject("_id", "1"); // to match your document
BasicDBObject update = new BasicDBObject("itemList", new BasicDBObject("itemID", "1"));
coll.update(match, new BasicDBObject("$pull", update));

Answer 2

The remove method from template removes document. If you want to remove item from array you have to use pull. Something like

MongoOperations mongoOperations = mongoConfiguration.getMongoTemplate();
Query query = new Query(where("_id").is(docID).and("itemList.itemID").is(itemID));
Update update = new Update().pull("itemList", new BasicDBObject("itemID", "1"));
mongoOperations.updateFirst(query, update, Item.class);