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From "DOAN DuyHai (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5590) User defined types for CQL3
Date Wed, 26 Feb 2014 15:43:28 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13913036#comment-13913036
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DOAN DuyHai commented on CASSANDRA-5590:
----------------------------------------

Another question about corner case.

 Currently CQL3 support list, set & map.

 The set structure respects a set contract, meaning that there is no duplicate. With primitive
types like text, bigint, date ... it's quite obvious to define equality.

 Now with custom user type, how do you manage equality ? Suppose that I define the custom
*address* type with several fields inside and I have a set<address>. How does Cassandra
enforce unicity ? Do you compare fields by fields ?  

> User defined types for CQL3
> ---------------------------
>
>                 Key: CASSANDRA-5590
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5590
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: API, Core
>            Reporter: Sylvain Lebresne
>            Assignee: Sylvain Lebresne
>             Fix For: 2.1 beta1
>
>         Attachments: ocd-and-corrections-patch.txt
>
>
> 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:
> {noformat}
> CREATE TYPE address (
>   street text,
>   city text,
>   zip_code int,
>   phones set<text>
> )
> CREATE TABLE users (
>   id uuid PRIMARY KEY,
>   name text,
>   addresses map<string, address>
> )
> {noformat}
> 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 a:
> {noformat}
> CREATE TYPE fullname (
>   firstname text,
>   lastname text
> )
> {noformat}
> and to rewrite the {{users}} table above as
> {noformat}
> CREATE TABLE users (
>   id uuid PRIMARY KEY,
>   name fullname,
>   addresses map<string, address>
> )
> {noformat}
> In terms of inserts we'd need a syntax for those new "struct". Could be:
> {noformat}
> 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...;
> {noformat}
> 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:
> {noformat}
> SELECT name.firstname, name.lastname FROM users WHERE id=2ad...;
> {noformat}
> One open question however is what type do we send back in the result set
> for a query like:
> {noformat}
> SELECT name FROM users WHERE id=2ad...;
> {noformat}
> 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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