Question

Assume that I have such entities like the following:

@Document(collection = "doc_a")
public class A {    
  @Field("id")
  private Integer id;

  @Field("b")
  private Collection<B> b;
  ...
}


public class B {    
  @Field("id")
  private Integer id;
  ...
}

is it possible to use a compoundIndex with respect to A.id AND B.id together?

I mean maybe like:

@CompoundIndex(name = "aid_bid_idx", def = "{'id', 'b.id'}")

Thanks in advance.

Answer 1

I’ve tried this kind of compound index in my app, that use spring data too, and worked properly.
You only have to correct the index definition in @CompoundIndex annotation:

@CompoundIndex(name = "aid_bid_idx", def = "{'id' : 1, 'b.id' : 1}")
@Document(collection = "doc_a")
public class A {    
  @Field("id")
  private Integer id;

  @Field("b")
  private Collection<B> b;
  ...
}

public class B {    
  @Field("id")
  private Integer id;
  ...
} 

If you run a query with explain (like the follows) in mongo shell, you’ll see that the index *aid_bid_idx* will be used.

db.doc_a.find({ "id" : 1, "b.id" : 1}).explain()

The result will be something like this:

{
    "cursor" : "BtreeCursor aid_bid_idx",
    ...
}