Why do I get an invalid path when I try and construct a JPQL join query?

Question

I’m using JPA 2.1, Hibernate 4.3.6.Final, and MySQL 5.5.37. How do I write a JPQL query that does a join? I’m trying below

    final String jpqlQuery = \"S         


        

Answer 1

The issue reported by Hibernate is in the first row:

final String jpqlQuery = "SELECT m FROM Message m LEFT JOIN MessageReadDate mr "...

in the LEFT JOIN statement. In hql, the JOIN must be expressing the relation, e.g.

LEFT JOIN m.MessageReadDate mr // the m is referencing the MessageReadDate

If there is no reference, we can still use that, but with Cartesian product

FROM Message m, MessageReadDate mr

in that case, the CROSS JOIN will be issued

See the:

• 16.2. The from clause

small cite:

Multiple classes can appear, resulting in a cartesian product or "cross" join.

from Formula, Parameter
from Formula as form, Parameter as param

• 16.3. Associations and joins

You can also assign aliases to associated entities or to elements of a collection of values using a join. For example:

from Cat as cat
    inner join cat.mate as mate