How can I use C*-side generation of UUID and TimeUUID?

[crazyproger]

I want make some handy save method on top of your API. Main idea is when entity does not have ID and it is of type UUID(90% case, i think) - let C* generate it on save, e.g. execute query like this: insert into stuff (uid, name) values(now(), 'my name');

I didn't find how to do this in project wiki. Can I do this in some way?

[valchkou]

UUID is very simple:

declare property as UUID: private UUID id; you can generate uuid as id = UUID.randomUUID();

TimeUUID more tricky as java has no built in support for it:

• Add dependency in project pom.xml (or add jar to your class path)

<dependency>
    <groupId>com.eaio.uuid</groupId>
    <artifactId>uuid</artifactId>
    <version>3.2</version>
</dependency>

• declare entity property as timeuuid @Column(columnDefinition="timeuuid") private UUID id;
• generate timeuuid UUID id = java.util.UUID.fromString(new com.eaio.uuid.UUID().toString());
• This function will convert timeuuid to date

import java.util.Date;
import java.util.UUID;

public class DateUtil {
    private static final long NUM_100NS_INTERVALS_SINCE_UUID_EPOCH = 0x01b21dd213814000L;

    public static Date timeUUID2Date(UUID uuid) {
        long time = (uuid.timestamp() - NUM_100NS_INTERVALS_SINCE_UUID_EPOCH) / 10000;
        return new Date(time);
    }
}

[crazyproger]

hmm, thanks. Interesting, but, I thought about calling CQL function. What you think, if I will make a pull-request with this possibility - can it be accepted by ideology of this project and integrated to it?

[valchkou]

OH sorry, got it, I was thinking to do it while back

[valchkou]

you are more than welcome to add such feature. I am thinking of custom annotation @TimeUUID instead of @Column(columnDefinition="timeuuid") with boolean optional parameter autogenerate or autosave. When set to true CQL will have now().

Another option (probably easier one) would be just to check if uuid is not set on entity then enchance CQL with the function now().

[valchkou]

available on mvn central. if uuid or timeuuid is a part of key and value is not set then C* functions uuid() or now() respectively will be used on insert. There is drowback though. The generated value will not be returned within save() operation.

[valchkou]

Default behavior is not to auto generate value. Autogen turned on only if id property annotated as @GeneratedValue

[crazyproger]

Oh, sadly to hear that generated values will not be returned. Very disappointing CQL limitation. But TimeUUID still helpful for clustering key fields when row used as smth like a timeline of events. Thanks for this feature.