Hi, I'm new to Hibernate and I have a problem which I have been googling it for hours. Basically, I have a one-to-many relationship between table A and table B. What I would like to do is to prevent a record from being inserted into table A unless its foreign key is actually referencing an existing record in table B. Does anyone know how to do this in Hibernate via JPA? Thanks

yes, easy: don't care about it as it will do that automatically.
Just make sure you define your model properly, then check the generated schema.

Can you give me some tips as to how to do it? I looked in the documentation but I could not find anything. Hibernate is not raising an exception when I insert a record which has a foreign key that references a non-existing record. Should I define the constraints at the database level?

that's obviously impossible, how could it store something violating the database constraints.
- did you disable database contraints (or run MySQL with MyISAM which doesn't support them)
- you're not mapping objects on the relations, but mapping primitives representing foreign keys


because it's trivial and automatic, but still Hibernate docs take the assumption people know how to work with databases.
You should first understand how to map objects and relations, I suspect that's the issue.. could you show a very simple relation?