Hi Francesco!
I usually let the PK be a String and create the UUID myself in Java.
The 'uuid' generator is a nice feature but it's not portable.
And that might be the reason why some DBs are not really working with it - it's
simply not that frequently used.
There are 3 ways to create the UUID.
a.) In the default ct. That might trigger a tad too often and might slow down
selects, etc.
b.) Lazily in getId(). If null -> create a new UUID
c.) Via an own ct which takes the UUID pk. You basically create the ID in your
business layer.
I mostly use c) if I need a UUID pk.
LieGrue,
strub
> On Monday, 11 April 2016, 9:02, Francesco Chicchiriccò <ilgro...@apache.org>
> wrote:
> > Hi all,
> I went further and built a sample POC [10] which mimics the essentials
> from Syncope.
>
> I have defined an UUIDGenerator implementing Seq (and relying on [3] for
> UUID generation), and declared it via
>
> @SequenceGenerator(name = "uuid", sequenceName =
> "net.tirasa.ilgrosso.uuidpoc.openjpa.UUIDGenerator()")
>
> in the @MappedSuperclass of both JPA entities available, plus defined
>
> @Id
> @GeneratedValue(strategy = GenerationType.SEQUENCE, generator =
> "uuid")
> private UUID id;
>
> in both entities.
>
> I have also extended the H2Dictionary to support the native UUID type
> (without such extension, the id column would have had type BLOB).
>
> All this above seems to work - at least for the simple JUnit test case
> provided; I have some questions, though:
>
> 1. I have experimented that UUIDGenerator is instantiated twice: would
> it be possible to defined it as singleton - as it happens for OpenJPA's
> UUIDType4HexSeq?
>
> 2. How would the @SequenceGenerator annotation translates to orm.xml?
> I've attempted the bare translation but it did not work.
>
> 3. The extended logic I have put in my H2Dictionary looks quite poor for
> the general case - even though good enough for my specific use case:
>
> @Override
> public String getTypeName(final Column col) {
> return col.getType() == Types.BLOB && (col.isPrimaryKey() ||
> col.isForeignKey())
> ? "UUID"
> : super.getTypeName(col);
> }
>
> How much difficult would be to make it proper, e.g. recognize when the
> class field is java.util.UUID? I'll need such extension for MySQL,
> MariaDB, PostgreSQL, MS SQL Server and Oracle dictionaries.
>
> 4. I am used to rely on openjpa-maven-plugin to generate the
> database.sql file; how can I configure it to use my H2Dictionary, and
> not the default?
>
> Thanks for your support.
> Regards.
>
> On 04/04/2016 10:49, Francesco Chicchiriccò wrote:
>> Hi all,
>> in Syncope we are currently discussing [1] the option to replace our
>> table generators-based id strategy to something else, based on UUID,
>> which seem to offer several advantages.
>>
>> I have found [2], but I would rather prefer to generated UUID values
>> manually (via [3] which seems to offer better performance and more
>> features than the standard JDK's).
>>
>> In order to do so, I would replace the current
>>
>> @Id
>> private Long id;
>>
>> public Long getKey() {
>> return id;
>> }
>>
>> in [4], backed by [5], with something like as
>>
>> @Id
>> private UUID id;
>>
>> public UUID getKey() {
>> synchronized(this) {
>> if (key == null) {
>> key = ... // generate via JUG [3]
>> }
>> }
>> return key;
>> }
>>
>> As Syncope supports several DBMSes, I would also like to empower the
>> underlying capabilities for storing such values:
>>
>> * UUID Type for PostgreSQL [6]
>> * UNIQUEIDENTIFIER for SQL Server [7]
>> * RAW(16) for Oracle [8]
>> * BINARY(16) with some optimizations for MySQL / MariaDB [9] or
>> vanilla with H2
>>
>> Do you have any suggestion about:
>>
>> (a) the way how I am planning to support UUID generation
>> (b) the cleanest way to support DBMS differences (extending the
>> respective DB dictionaries?)
>>
>> TIA
>> Regards.
>>
>> [1] http://markmail.org/message/fhdrwerdwdm3opdx
>> [2]
>>
> http://openjpa.apache.org/builds/2.4.1/apache-openjpa/docs/jpa_overview_meta_field.html#jpa_overview_meta_gen
>> [3] https://github.com/cowtowncoder/java-uuid-generator
>> [4]
>>
> https://github.com/apache/syncope/blob/master/core/persistence-jpa/src/main/java/org/apache/syncope/core/persistence/jpa/entity/user/JPAUser.java
>> [5]
>>
> https://github.com/apache/syncope/blob/master/core/persistence-jpa/src/main/resources/META-INF/spring-orm.xml#L87-L94
>> [6] http://www.postgresql.org/docs/9.3/static/datatype-uuid.html
>> [7]
>> http://wiki.ispirer.com/sqlways/sql-server/data-types/uniqueidentifier
>> [8]
>>
> http://docs.oracle.com/cd/B28359_01/server.111/b28286/functions175.htm#SQLRF51816
>> [9] https://www.percona.com/blog/2014/12/19/store-uuid-optimized-way/
> [10] https://github.com/ilgrosso/OpenJPAUUIDPOC
>
>
> --
> Francesco Chicchiriccò
>
> Tirasa - Open Source Excellence
> http://www.tirasa.net/
>
> Involved at The Apache Software Foundation:
> member, Syncope PMC chair, Cocoon PMC, Olingo PMC, CXF committer
> http://home.apache.org/~ilgrosso/
>
