[hibernate-issues] [Hibernate-JIRA] Created: (HHH-5352) Misleading replacement of commas with cross joins

[Patras Vlad (JIRA)]

Misleading replacement of commas with cross joins
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                 Key: HHH-5352
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-5352
             Project: Hibernate Core
          Issue Type: Bug
    Affects Versions: 3.5.3, 3.5.2, 3.5.1, 3.5.0-Final, 3.5.0-CR-2, 3.5.0-CR-1, 3.5.0-Beta-4, 3.5.0-Beta-3, 3.5.0-Beta-2
         Environment: Hibernate 3.5.3
Ms SQL Server 2005
            Reporter: Patras Vlad


  There was a new feature implemented in 3.5.0-Beta-2: HHH-1480, as a result, for many dialects, the comma operator "," was replaced with "cross join". As it's already obvious from the feature's description, this changes join precedence. If the query contains outer joins (left or right) this replacement changes the results (because outer join precedence is important).
  This might not be interpreted as a bug if you know what SQL operator will be generated when you place a comma in HQL, but it's misleading if you don't. A HQL query like:

{noformat}select a from A a, B left join B.c c{noformat} 

is not equivalent with the SQL query:

{noformat}select a.* from A.a, B b left join C c on b.cid = c.id{noformat} 

because the actual SQL query is:

{noformat}select a.* from A.a cross join B b left join C c on b.cid = c.id{noformat}

The first SQL query would make a left join on B and C and then a cross join with the result and A (and this is what we should expect). The second SQL query makes a cross join on A and B and then a left join with the result and C (this is not expected since we had a comma in HQL).

I understand the issues presented in HHH-1480, but they should be expected, i.e. a developer SHOULD expect a faliure from a query like 
{noformat}select a from A a, B b join a.c C{noformat}
because "a" is not visible in the join. Hibernate should not use a cross join behind the scenes to allow such a query at the expense of providing misleading results for others.

Maybe turn this into a feature/improvement or add another to allow explicit comma or croos join in HQL, or support parenthesis in HQL.

The only workaround I can see for now is to re-order the query like this:

{noformat}select a from B left join B.c c, A a{noformat} 

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