I seem to have found a race condition that overwrites rows in the join table in a @ManyToMany relationship. Here's a simplified example:

class Employee {
@Id
@Column( name = "EMPLOYEE_ID" )
private long id;

@Column( name = "NAME" )
private String name;

@ManyToMany( mappedBy = "employees", cascade = CascadeType.ALL )
private List< Employer > employers = new ArrayList< Employer >();
}

class Employer {
@Id
@Column( name = "EMPLOYER_ID" )
private long id;

@ManyToMany
@JoinTable( name = "JOIN_TABLE", joinColumns = { @JoinColumn( name = "EMPLOYEE_ID" ) }, inverseJoinColumns = { @JoinColumn( name = "EMPLOYER_ID" ) } )
private List< Employee > employees = new ArrayList< Employee >();
}


My code looks something like:

Employee john = new Employee();
john.setName( "John" );
Employer employer = employerDao.findEmployer( employerName );
john.getEmployers().add( employer );
employer.getEmployees().add( john );
employeeDao.persist( john );


While running single-threaded, everything works perfectly. However, when running multi-threaded, the entries in the JOIN_TABLE are not consistently persisted. For instance, say I am trying persist employee "John" and employee "Jane", both linked to the same employer, in two different threads with two different transactions. Occasionally, after both threads commit, the JOIN_TABLE only includes a mapping from "Jane" to the employer, and "John" is nowhere to be seen. No exceptions are thrown.

I noticed that if I change the order of the mappings by making the Employee the "parent" association, it always works as expected.

Has anyone seen this error before? Is it a bug, or am I doing something wrong?

I'm using Hibernate Annotations 3.4.0.GA, Hibernate Core 3.3.2.GA, and Hibernate Entity Manager 3.4.0.GA. Spring 2.5.5 and Bitronix 1.3.3 are also in use.

Thanks,
Dan Nawrocki