How to properly cast string to number with JPA2 Criteria API?

I am trying to write a query with subselect where a string is cast to a long. I'm probably missing something?

Query looks like:

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Task> query = cb.createQuery(Task.class);

Root<Task> from = query.from(Task.class);

Subquery<Long> subquery = query.subquery(Long.class);
Root<EntityKeyword> fromKeyword = subquery.from(EntityKeyword.class); 
subquery.select(fromKeyword.get(EntityKeyword_.relatedToId).as(Long.class));
subquery.where(cb.like(fromKeyword.get(EntityKeyword_.keyword), term));

query.where(cb.in(from.get(ModelEntity_.id)).value(subquery));

Where EntityKeyword_.relatedToId a is String that requires cast to Long.

But underlying Hibernate fails with exception:

Last cause: No data type for node: org.hibernate.hql.ast.tree.MethodNode 
 \-[METHOD_CALL] MethodNode: '('
    +-[METHOD_NAME] IdentNode: 'cast' {originalText=cast}
    \-[EXPR_LIST] SqlNode: 'exprList'
       +-[DOT] DotNode: 'entitykeyw1_.keyword' {propertyName=keyword,dereferenceType=ALL,propertyPath=keyword,path=generatedAlias1.keyword,tableAlias=entitykeyw1_,className=l.i.s.m.s.EntityKeyword,classAlias=generatedAlias1}
       |  +-[ALIAS_REF] IdentNode: 'entitykeyw1_.id' {alias=generatedAlias1, className=l.i.s.m.s.EntityKeyword, tableAlias=entitykeyw1_}
       |  \-[IDENT] IdentNode: 'keyword' {originalText=keyword}
       \-[IDENT] IdentNode: 'int8' {originalText=int8}

No idea what's wrong. Any help is appreciated.

I'm using Hibernate 3.6.8-Final

There is no method in Criteria API that performs conversion from String to Long.

You try to use method as in Expression to make this conversion. Javadoc explains why you end up to have runtime problems:

Perform a typecast upon the expression, returning a new expression object. This method does not cause type conversion: the runtime type is not changed. Warning: may result in a runtime failure.

CriteriaBuilder does have bunch of methods for typecast, but also no support for string-to-numeric conversion.