I am running a transaction to save an object to the database.
One of the properties is a string and I have set the length property in the mapping file.

I can set this property to a string of any length. However, when I try to persist it an exception is thrown on the call to transaction.Commit. It is a database exception telling me that the string is too long for the field.

Now, I would have expected NHibernate to have warned me before even giong to the database, since this information is in the mapping file.

Am I right to expect this or is there something I should do for this to happen?

Otherwise, are there any ways around this.. without testing the property in the class... since I do want to seperate out the database from the domain model, so I don't want to limit the field sizes in my classes.

Did you ever find a solution to this?

I too have the same concern and it seems "right" for hibernate to "represent" what it persists.

I believe that length field is only used when generating DDL from the hbm files.

this is true. and to a certain extent your UI should perform some validation and constraint checking (imho).

-devon

IMHO, the GUI should know nothing of the data storage system. Isn't that the whole point of uing OR Mapping?

My feeling is that the data constraint checking should be carried out by the OR Mapper, since this is the first point at which there is knowledge about the underlying data structure.

The UI should perform length validation so you can immediately flag a field as being invalid and give the user instant feedback before pressing "submit" button, etc.

However, the data layer should also perform this validation to intelligently handle programmatic access to the data.

We handle this by having the string properties on our entities enforce the max length in their setter. We also decorate the property with a custom attribute that defines this max length, so that the UI can discover the max length and enforce it before actually trying to set the property. While this makes the max length redundant in two places, we don't have a problem with that because our entities are generated from the mapping files.