Currently, it seems like ID needs to be appear in parent and child for nested documents. But it is unlikely a case for MongoDB customers. It would be nice if Teiid can flatten out data in one single table. Therefore, users would not need to insert parent id in the child document in order for Teiid to work.

I am thinking the following case. For example I have a JSON object like this:

 
Customer
{
  _id: 1374932,
  FirstName: "John",
  LastName: "Doe",
  Address:  {
       _id: 43839430,
        Street: "123 Lane",
        City: "New York",
        State: "NY",
        Zipcode: "12345"
     }
}

In this case, customer._id doesn't exist inside Address. There is no way to do join in regular SQL fashion. But it would be nice if teiid can put the column from parent and child into a single table. Maybe something similar to the following schema:

CREATE FOREIGN TABLE  Customer (
    CustomerId integer PRIMARY KEY,
    FirstName varchar(25),
    LastName varchar(25),
    address__id integer,
    address_Street varchar(50),
    address_City varchar(25),
    address_State varchar(25),
    address_Zipcode varchar(6),
) OPTIONS(UPDATABLE 'TRUE');