Hi,

I dont know if I'm missing something but it looks pretty strange to me that the "default" sequence name is "hibernate_sequence".
AFAIK the "default way" to name sequence in Postgresql is <table name>_<column name>_seq and thus that ought to be the default name ?
But I'm new to postgres as well as to hibernate so I could be mistaken.

To summarize my problem:

My create sql command:



This gives a default value:


Which really is <table name>_<column name>_seq (and not as hibernate anticipates hibernate_sequence).

The following generator mapping works like a charm:


But none of the following one does:



Both generate the faulty SQL query:


(which generates an SQL error)

Perhaps there is a way to configure the name ? (though I have yet to find it)

I, to see if it was "imposible to solve", quickly wrote my own generator that works as I belive it "should" by changing the following line:

into:


Which seem to work "like a charm" ofcource perhaps this way should be made optional and configureable but I only wanted to get things working so it is a crude way to fix the problem. I think that a way to specify the default name using variables would be the preferable solution.
ie something along the following:
<property name="hibernate.sequence_name">${target_table}_${target_column}_seq</property>
in the hibernate.cfg.xml file ?
This would then ofcource fallback to "hibernate_sequence"... But as I dont know my way around hibernate I solved it the "simple way".


Anyways if anyone know how I can make hibernate to behave as I want it or if there is something wroing with my reasoning point me at how I should change things please let me know.


// Michael Medin

You are making it very complicated for yourself. Using serial as the column type is not needed.


Try:

Create Table




Mapping



You will not have to touch the sequence at all.


Cheers,


Sherman

you need to issue a CREATE SEQUENCE for the hibernate_sequence of course.

== Ezra Epstein

Hi,

I know I can create a sequence for hibernates key and in the other sample use another name for the sequence (one that I specify).

But I want to use hibernate to access and existing database that will be use for other purpouses then hibernate not create a hibernate only database thus I would prefer to have a more generic solution one that will function transparently with other access gateways.

Also as I understand it the "default way" to create sequences is using <table name>_<column name>_seq so using another name for it seems "wrong".

And the other idea

suffers from the same problem I have as it is not "normalized" as it uses information that is already avalible (ie. the sequence is named the same as <table name>Seq so my proposed solutions abpove would benefit this version also).


// Michael Medin

The "default way" for sequence naming is driven by your use of the "serial" column in your table definition. See http://www.postgresql.org/docs/current/interactive/datatype.html#DATATYPE-SERIAL

Hibernate does not understand that Postgres your "identity" column, based on the dialect definition. It understands using sequences to populate an ID column, though. When it inserts a row in a table for an object with a "sequence" id, it will run a query to get the next sequence value, set the id in the object, and then save the object with another query. See http://www.hibernate.org/hib_docs/reference/html/or-mapping.html#or-mapping-s1-4-sequences

Postgres sequences use bigint arithmetic. See http://www.postgresql.org/docs/current/interactive/sql-createsequence.html.. Any column being populated from a sequence should be an INT8, and a Long in a Hibernate schema mapping.

If you change your id column to an INT8 rather than serial in the CREATE TABLE, and create the sequence separately, then the scheme I gave before will work.


Sherman

Yes, but again the database is not designed for hibernate but rather hibernate is beeing "designed" for my database thus I cannot (or rather willnot as I feel it to be the "wrong way") alter the database. And besids the type does not matter Serial is as you say an "integer" type with a default sequence added for convenience no mater what type I will still call my sequence <table name>_<colum name>_seq as that is what is recomended by postgresql.

I also still feel that a persistance framework should not force the database to use names that are persistance layer specific thus I wanted an abstracted solution. Something you get by allowing the table name to be specified in the configuration. I canot se any benefit to having "hibernate_sequence" as the default (and only generic) sequence naming. As the name is by defenition hibernate specific. Again I could be misunderstanding this.


But I sopose I should stick with my own generator then if there is no way to make hibernate work "my way". As that allows me to have a generic database that is mapped to other persistance frameworks as well as hibernate.

Anyways, thanx for the input...


// Michael Medin

One thing you might want to try is creating a subclass of the PostgreSQLDialect that implements the supportsIdentityColumns and related methods. Grab the Hibernate2 source and look at what the DB2Dialect does. Then you could use sequence="identity" in your mapping.

You may also want to put in a feature request to the Hibernate JIRA.


Sherman