Querying nested objects in SpringData MongoDb

Question

I need to ask a question about a nested object state in my document, which looks like this:

{
  "_id" : ObjectId("5437248f2dfbc82fcafa9733"),
  "_class" : "conference.Speaker",
  "speakerId" : NumberLong(0),
  "name" : "John Doe",
  "talks" : [{
      "talkId" : NumberLong(0),
      "when" : ISODate("2014-10-17T15:00:00Z"),
      "title" : "Stuff"
    }]
}

This document looks fine and it is generated out of 2 classes, Speaker and Talk, when none of them have any annotations and the former has a List of the laters as a property.

What I need to get is a list of talks with certain name. Here's what I am tring to do:

BasicQuery query = new BasicQuery("{'talks.title' : 'Stuff'}");

This fails with org.springframework.data.mapping.model.MappingException: Invalid path reference talks.title! Associations can only be pointed to directly or via their id property!

I guess it can't use the Id property (since Talk object doesn't have it's own id), and I have no idea what 'can be pointed directly means'.

What's wrong with my query and/or the mapping?

I guess it's because talks is an array. To be pointed directly, it should be talks.index.title (index = 0, 1, ...) - of course this style is out of your expectation. Another way is: Query query = new Query().addCriteria(Criteria.where("talks.title").is("Stuff"));. Not sure if it's what you want. — Wizard
– Wizard, Commented Oct 10, 2014 at 2:18

MirceaG · Accepted Answer · 2015-02-11 16:54:44Z

1

Regarding the error you'll have to give more details: the exact call that is throwing the error, SpringData version, MongoDB version.

The query that you built seems ok, but it won't return Talk objects, but instead will return Speaker objects that have at least one 'Stuff' talk.

If you want to get only one Talk that has a certain title you can use a find with a projection:

db.talks.find({"talks.title":"Stuff"}, { talks: { $elemMatch: { title: "Stuff" } } })

If you'd like all the Talks matching a title you'll have to use an aggregation:

    db.talks.aggregate(
       // match only speaker with 'Stuff talks'
       { $match : {
          "talks.title": "Stuff"
       }},
       { $unwind : "$talks" },
       { $match : {
          "talks.title": "Stuff"
       }},
       // projection (only talks fields?)
     )

answered Feb 11, 2015 at 16:54

MirceaG

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