hibernate - createCriteria or createAlias?
If I want to search those students who take class "Math" and "John" is his group:
shoud I use createCriteria or createAlias?
Criteria:
Criteria criteria = session.createCriteria(Student.class);
Criteria subquery1 = criteria.createCriteria("courses", course).add(Restrictions.eq(course.name, "Math"));
Criteria subquery2 = criteria.createCriteria("group", student).add(Restrictions.eq(student.name, "John"));
how 开发者_如何学JAVAto put subquery1 and subquery2 together with initial criteria?
Alias:
Criteria criteria = session.createCriteria(Student.class).
createAlias("courses", course).add(Restrictions.eq(course.name, "Math")).
createCriteria("group", student).add(Restrictions.eq(student.name, "John"));
When to use createCriteria and when createAlias? I think the boath are the same...
CreateAlias and CreateCriteria are identical in the current versions of Hibernate and NHibernate. The only difference being that CreateCriteria has 2 additional overloads without the alias parameter.
Presumably they were different in a older version, but any differences are long gone.
An alias can be defined in terms of another alias, so your first example can be written as:
// Java
Criteria criteria = session.createCriteria(Student.class)
.createAlias("courses", "course")
.createAlias("course.group", "student")
.add(Restrictions.eq("course.name", "Math"))
.add(Restrictions.eq("student.name", "John"));
// C#
ICriteria criteria = session.CreateCriteria<Student>()
.CreateAlias("Courses", "course")
.CreateAlias("course.Group", "student")
.Add(Restrictions.Eq("course.Name", "Math"))
.Add(Restrictions.Eq("student.Name", "John"));
Adding to xavierzhoa's answer:
There is actually quite a big difference between the two methods which you will notice if you chain Criteria
methods. You will continue to work on the original Criteria
object when using createAlias
, whereas you work on a more nested scope when using createCriteria
.
Consider this:
Criteria c = getSession()
.createCriteria(YourEntity.class)
.createCriteria("someMember", "s")
.add(Restrictions.eq("name", someArgument)); // checks YourEntity.someMember.name
versus
Criteria c = getSession()
.createCriteria(YourEntity.class)
.createAlias("someMember", "s")
.add(Restrictions.eq("name", someArgument)); // checks YourEntity.name
However, if you always assign and use an alias you will be able to work around the difference. Like:
Criteria c = getSession()
.createCriteria(YourEntity.class, "y")
.createAlias("someMember", "s")
.add(Restrictions.eq("y.name", someArgument)); // no more confusion
Please refer to the following source code from the Hibernate
public Criteria createCriteria(String associationPath, String alias, int joinType) {
return new Subcriteria( this, associationPath, alias, joinType );
}
public Criteria createAlias(String associationPath, String alias, int joinType) {
new Subcriteria( this, associationPath, alias, joinType );
return this;
}
Criteria criteria = (Criteria)sessionFactory.getCurrentSession().createCriteria(BillEntity.class)
.createAlias("worksEntity", "worksEntity" ,JoinType.LEFT_OUTER_JOIN)
instead of writing (Jointype) use the import file as
(org.hibernate.sql.JoinType..LEFT_OUTER_JOIN)
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