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From "Sylvain Lebresne (JIRA)" <>
Subject [jira] [Created] (CASSANDRA-5590) User defined types for CQL3
Date Thu, 23 May 2013 17:41:21 GMT
Sylvain Lebresne created CASSANDRA-5590:

             Summary: User defined types for CQL3
                 Key: CASSANDRA-5590
             Project: Cassandra
          Issue Type: New Feature
            Reporter: Sylvain Lebresne

A typical use case for a collection could be to store a bunch of addresses in a user profile.
An address could typically be composed of a few properties: say a street, a city, a postal
code and maybe a few phone numbers associated to it.

To model that currently with collections, you might use a {{map<string, blob>}}, where
the map key could be a string identifying the address, and the value would be all the infos
of an address serialized manually (you can use {{text}} instead of {{blob}} and shove everything
in a string if you prefer but the principle is the same).

This ticket suggests to make this more user friendly by allowing:
CREATE TYPE address (
  street text,
  city text,
  zip_code int,
  phones set<text>

  id uuid PRIMARY KEY,
  name text,
  addresses map<string, address>

Under the hood, that type declaration would just be metadata on top of CompositeType (which
does mean a limitation would be that we wouldn't allow re-ordering or removal of fields in
a custom TYPE). Namely, the {{address}} type would be in practice a {{CompositeType(UTF8Type,
UTF8Type, Int32Type, SetType(UTF8Type))}} + some metadata that records the name of each component.
 In other words, this would mostly be user-friendly syntactic sugar to create composite blobs.

I'll note that this would also be useful outside collections, as it might sometimes be more
efficient/useful to have such simple composite blob. For instance, you could imagine to have
CREATE TYPE fullname (
  firstname text,
  lastname text
and to rewrite the {{users}} table above as
  id uuid PRIMARY KEY,
  name fullname,
  addresses map<string, address>

In terms of inserts we'd need a syntax for those new "struct". Could be:
INSERT INTO users (id, name)
           VALUES (2ad..., { firstname: 'Paul', lastname: 'smith'});
UPDATE users
   SET addresses = address + { 'home': { street: '...', city: 'SF', zip_code: 94102, phones:
{} } }
   WHERE id=2ad...;
where the difference with a map is that the "key" would be a column name (in the CQL3 sense),
not a value/literal. Though we might find that a bit confusing and find some other syntax.

On the query side, we could optionally allow things like:
SELECT name.firstname, name.lastname FROM users WHERE id=2ad...;

One open question however is what type do we send back in the result set
for a query like:
SELECT name FROM users WHERE id=2ad...;
We could:
# return just that it's the user defined type named {{address}}, but that imply the client
has to query the cluster metadata to find out the definition of the type.
# return the full definition of the type every time.

I also note that client side, it might be a tad harder to support such types cleanly in statically
type languages than in dynamically typed ones, but that's not the end of the world either.

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