A database language is extended to define constraints on a data model (e.g., entity-relationship model) rather than the concrete database. The constraints can be declarative (e.g., constraints that are defined using expressions of the database language) or programmatic (e.g., constraints that are defined as a stored procedure implemented in a domain specific language). By storing the constraints at a higher level than the database level, the constraints can be performed without changing the persistency of the database. Also disclosed are techniques for handling of constraints on partially loaded entities.