Hibernate version:1.0.2

Hi there,

i'd like to map a table, but the table hasn't a identifier/primary key field. Now NHibernate throws an error that it must have an identifier. How can I resolve this?

Thanks.

If you can, add a primary key to the table. Can you infer a natural (composite) key? How do you identify one unique record?

Hi,

thank you for your respone and sorry for the delay. One column has an index but the column isn't unique. Currently I open the database with the OleDbConnection and add a column with the alter statement and use that column as primary key. Then I use NHibernate. When I have finished working with the DB I drop the column.

The problem is that I didn't create the DB. It's from a third party.

Maybe for one of the next releases of NHibernate it's possible to allow tables without index. I know it's against the normal form but tell that the people who build the database I have to use.

There's no way that I know of for NHibernate to work with a table where rows are not guaranteed to be unique be either a surrogate key (primary key) or a natural key (joined primary keys). If you can't find a way to identify one row from another, you'll likely have trouble with any ORM solution.

If I have a table like:


... and there's no definitive way to know that row2 != row1, I would have to scan all the fields in all the rows looking for duplicates, or put the rows in different sets of Hashtables to find duplicates. That would be horrendously slow! It just won't work. And how would you look up mike's row, by name? If there's a primary key column, indexed and unique, is much faster than Now you've given the select statement all the info you needed to retrieve, making the query pointless. Also, the DB has to scan the value of all those fields to find the value you've given, rather that getting a match from an index.

Tables without primary or composite keys just won't work - that's why NHibernate requires it.