Unique colums automatically defined as non-nullable
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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
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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