Querydsl generates invalid SQL on basic aggregate query - sql-server

Question

I am using QueryDSL and Hibernate to query a SqlServer2008 database.
I have a Sessions table that contains a sessionId column. I want to obtain the max sessionId.
I run the following query:
QSessions session = QSessions.sessions;
HibernateSQLQuery query = new HibernateSQLQuery(sessionFactory.openSession(), new SQLServer2005Templates());
query.from(session).list(session.sessionId.max());
My hibernate.cfg.xml:
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.url">jdbc:sqlserver://SVR;databaseName=DB</property>
<property name="hibernate.connection.username">X</property>
<property name="hibernate.connection.password">X</property>
<property name="hibernate.connection.driver_class">com.microsoft.sqlserver.jdbc.SQLServerDriver</property>
<property name="hibernate.dialect">org.hibernate.dialect.SQLServer2008Dialect</property>
<mapping class="com.coveo.data.Sessions" />
</session-factory>
</hibernate-configuration>
When I run the query, I can see that Hibernate attempts to run the following SQL query:
17:36:10.011 [main] DEBUG org.hibernate.SQL - select max(sessions.*.sessionId) as col__1 from sessions
This is not valid SQL. I would have expected
select max(sessions.sessionId) as col__1 from sessions
When Hibernate attempts to execute the query, I get the following error:
com.microsoft.sqlserver.jdbc.SQLServerException: Incorrect syntax near '*'.
I get the same syntax error when attempting to run the invalid SQL query using SQL Management Studio.
Why does Querydsl require a dialect? Isn't Hibernate in charge of generating the SQL?
Why is the generated SQL invalid?
EDIT: I get the same behavior when using .avg(), .min() or another aggregate function.

Answer 1

I ended up switching to jOOQ.
So far, the experience has been very positive. The API is somewhat similar, the documentation is better and it doesn't generate invalid SQL.

Answer 2

There are a few issues here.
You use HibernateSQLQuery which is meant to execute SQL queries through the Hibernate API, please use HibernateQuery for Hibernate ORM queries
You use the Q-type generated for ORM queries in SQL queries. Querydsl should handle this usage better and I created a ticket for it https://github.com/mysema/querydsl/issues/463
Querydsl supports both ORM and SQL based queries for Hibernate and you accidently mixed them.
For normal Hibernate queries your example would be
QSessions session = QSessions.sessions;
HibernateQuery query = new HibernateQuery(sessionFactory.openSession());
query.from(session).list(session.sessionId.max());
I assume that QSessions is based on the Sessions entity.
jOOQ is a very good alternative for the SQL level, but if you need to access also JPA and NoSQL based storages, Querydsl offers more.