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From "Martin Dirichs (JIRA)" <j...@apache.org>
Subject [jira] Commented: (OPENJPA-1387) Unique colums automatically defined as non-nullable
Date Mon, 16 Nov 2009 10:26:41 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-1387?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12778287#action_12778287
] 

Martin Dirichs commented on OPENJPA-1387:
-----------------------------------------

Just noticed that there exists an exceptional database not capable of unique contraints on
nullable fields: Apache Derby, versions up to 10.4.1.3. In 10.4.1.3, this shortcoming was
fixed, see here:
http://issues.apache.org/jira/browse/DERBY-3330
OpenJPA currently uses Derby 10.2.2.0 for its test cases. Thus, there are build failures after
applying this patch. There are three possibilities of how to deal with this:
1. Eliminate the problem by updating to a more recent Derby version.
2. Modify the test cases so that @Column(nullable=false) is explicitly stated where necessary.
3. Continue to label columns implicitly as non-nullable as database-specific logic. Do it
for Derby < 10.4.1.3 and maybe some other database out there I am not aware of, leave it
for all others (default).

> Unique colums automatically defined as non-nullable
> ---------------------------------------------------
>
>                 Key: OPENJPA-1387
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-1387
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: sql
>    Affects Versions: 2.0.0-M3
>         Environment: Error happens in every environment.
>            Reporter: Martin Dirichs
>            Assignee: Pinaki Poddar
>             Fix For: 2.0.0-M4
>
>         Attachments: OpenJPA-Trunk_OJ1387.patch
>
>
> Any unique constraint declared with OpenJPA implicitly sets the respective columns to
be non-null. This is a problem if OpenJPA's mapping tool is used to create the database schema.
Even if something like @Column(nullable=true) is explicitly stated, the columns will always
be created by OpenJPA as not null.
> Modifying the database schema manually to make the columns nullable is a possible workaround.
It does not seem to cause any problems with either OpenJPA or the databases.
> I would suggest to drop the marking of unique columns as not nullable. This is done by
removing the corresponding code lines in org.apache.openjpa.jdbc.schema.Unique (trivial patch
appended to this issue). If someone wants a unique column to be not nullable, this can be
specified explicitly with @Column(nullable=false) as usual.
> I can only speculate about the reason this strange coupling of unique and nullable had
been introduced into OpenJPA. To my knowledge, it is perfectly legal use to have unique contraints
on nullable columns. In effect this means that there may be multiple rows with null values,
whilst all rows with non-null values have to be unique. ANSI SQL-92 also explicitly mentions
nullable unique columns and states that this is a crucial difference between PRIMARY KEY columns
and UNIQUE columns: the former are always not nullable, the latter may be nullable.
> This issue also pops up again and again in the user discussions, without (to my knowledge)
a single authorative answer to why this behaviour is as it is in OpenJPA. Two examples:
> My question, which remained unanswered:
> http://n2.nabble.com/Unique-colums-automatically-made-NOT-NULL-td2827809.html
> Another users question, about a month later:
> http://n2.nabble.com/Nullable-unique-constraints-td3161182.html

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