[Sqlalchemy-tickets] Issue #3503: add full control for return type under PG ARRAY, HSTORE, JSON, JSONB indexed (element) access (zzzeek/sqlalchemy)

[Mike B. <iss...@bi...>]

New issue 3503: add full control for return type under PG ARRAY, HSTORE, JSON, JSONB indexed (element) access
https://bitbucket.org/zzzeek/sqlalchemy/issues/3503/add-full-control-for-return-type-under-pg

Mike Bayer:

e.g., if I want myhstorecol['somecol'] to have a custom type, how do I do that?  Some system that works for all of these types that defines the return types for indexed access should be devised.

1.1 because this is like a big deal, it's going to come up a lot, but no concrete plan right now.

Perhaps a "schema" dictionary.  "*" is a wildcard:


```
#!python

HSTORE(schema={'*': String})
JSON(schema={'subdict': JSON(schema={'elements': ARRAY(Integer)}})
HSTORE(schema={'foob': String, 'bar': MyMagicType})


```


dictionary too coarse-grained?  Supply a callable instead:


```
#!python

HSTORE(schema=lambda key: String if key =="foo" else MyMagicType)
```