Java / Hibernate: Could not resolve property with nested object criterias

You can’t use nested paths directly in Criteria API (unlike HQL). Instead, you need to create nested criteria instances or define aliases on each “entity.property” pair starting with the first non-root entity:

Criteria criteria = session.createCriteria(Enquiry.class)
 .createAlias("lecture", "l")
 .createAlias("l.admin", "a")
 .add( Restrictions.eqProperty("a.id", userId) );

Note that the very first property is not prefixed as it belongs to the root entity (Enquiry), the others are prefixed with previous level alias. Details are in the documentation.

Also note that id is a special property when it comes to associations; in your case user_fk is a column located in lecture table. It should, therefore, be possible (provided that the mappings you’ve posted are accurate) to rewrite the above criteria as:

Criteria criteria = session.createCriteria(Enquiry.class)
 .createAlias("lecture", "l")
 .add( Restrictions.eqProperty("l.admin.id", userId) );

thus eliminating extra join.