Investigate JSON filtering on Postgres and Mongo.

[wtrocki]

For subscriptions? or general?

[machi1990]

This follows up https://github.com/aerogear/graphback/pull/1749#issuecomment-664399567 where the database queries are not properly mapped hence causing issues.

/cc @craicoverflow

[machi1990]

To query nested objects / array in Mongo:

• Objects: https://docs.mongodb.com/manual/tutorial/query-embedded-documents/
• Array: https://docs.mongodb.com/manual/tutorial/query-array-of-documents/, more or less the same as for embedded docs with an additional of array operators

For Postgres:

• Top level https://www.postgresql.org/docs/current/datatype-json.html e.g containment, equality
• Field level filtering can be achieved via json path accessors (https://www.postgresql.org/docs/current/datatype-json.html#DATATYPE-JSONPATH)

Dumping the links here to drive the investigation later on.