Is there any converter for UUID type in playORM?

Question

I would like to map a field with type UUID. I am generating it like follows:

import java.util.UUID; UUID id = UUID.randomUUID();

Is there any problem in using this? What converter could I use for this?

Answer 1

random != unique. At very very very high numbers, you may collide. Some people are ok with this....I prefer to avoid it as even though the probability could be somewhere near 1 in 1 billion, if it happens, debugging it is a PITA.

Also, At very very very high numbers, you get more likely to collide.

Read this link

http://johannburkard.de/blog/programming/java/Java-UUID-generators-compared.html

Basically, I looked at his code once and to be unique, it is really mac address + UNIQUE timestamp within that computer, so two threads are not allowed to grab the same timestamp.

In fact, if you use @NoSqlId, it is actually using unique counter from timeA + hostname so it is unique within one cluster. One client uses hostnames of a1, a2, a3 which keep the primary key nice and short. I never thought about it before but if I added @NoSqlIndex on the key, I could query ranges of keys and they are in order of time.

I should probably create another generator that is time based so people can use as primary key and query time ranges(add an issue if this will be useful for you as I work in order of what clients need rather than what I think is needed).

For the above to answer your question. you can create the Converter and when going from byte[] to UUID, you can just use

public static UUID nameUUIDFromBytes(byte[] name)

Going backwards though, you need to do the opposite of that function which from the java source code is

public static UUID nameUUIDFromBytes(byte[] name) {
    MessageDigest md;
    try {
        md = MessageDigest.getInstance("MD5");
    } catch (NoSuchAlgorithmException nsae) {
        throw new InternalError("MD5 not supported");
    }
    byte[] md5Bytes = md.digest(name);
    md5Bytes[6]  &= 0x0f;  /* clear version        */
    md5Bytes[6]  |= 0x30;  /* set to version 3     */
    md5Bytes[8]  &= 0x3f;  /* clear variant        */
    md5Bytes[8]  |= 0x80;  /* set to IETF variant  */
    return new UUID(md5Bytes);
}

thanks, Dean