Using Hibernate criteria fetch properties of two objects

Question

Getting Exception while running query using Criteria API

 org.hibernate.QueryException: could not resolve property: com of: com.data.Collage        at org.hibernate.persister.entity.AbstractPropertyMapping.propertyException(AbstractPropertyMapping.java:44)
    at org.hibernate.persister.entity.AbstractPropertyMapping.toType(AbstractPropertyMapping.java:38)
    at org.hibernate.persister.entity.AbstractEntityPersister.toType(AbstractEntityPersister.java:1362)
    at org.hibernate.loader.criteria.CriteriaQueryTranslator.getPathEntityName(CriteriaQueryTranslator.java:204)
    at org.hibernate.loader.criteria.CriteriaQueryTranslator.createCriteriaEntityNameMap(CriteriaQueryTranslator.java:191)
    at org.hibernate.loader.criteria.CriteriaQueryTranslator.<init>(CriteriaQueryTranslator.java:81)
    at org.hibernate.loader.criteria.CriteriaLoader.<init>(CriteriaLoader.java:58)
    at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1550)
    at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:283)

Having class definitions as follow

class Collage {
int id;
String collageName;
List lstStudent;
}

class Student{
String studentName;
int id;
}

Have done mapping for above classes.

Now I am trying to fetch collage name and student name in single query where I have collageID and StudentID with me. Used Criteria API for this.

Criteria cr = session.createCriteria("com.data.Collage","collageAlias");
cr.createAlias("com.data.Student","studentAlias");
cr.add(Restrictions.eq("collageAlias.id", "402882c2369bc53901369bc95d5f0137"));
cr.add(Restrictions.eq("studentAlias.id","ff80808134cbe5a10134d14ff20300a9"));

ProjectionList properties = Projections.projectionList();
properties.add(Projections.property("collageAlias.collageName"));
properties.add(Projections.property("studentAlias.studentName"));

cr.setProjection(properties);
List collage_student = cr.list();

I have try with Collage.class, removed alias name for collage as t's default class for criteria API, But it didn't work.

Any suggestion?

Answer 1

When you do

cr.createAlias("com.data.Student","studentAlias");

Hibernate automatically thinks that Student is a field of the Collage class, as the criteria is built on that class. By creating an alias you automatically make a join on that particular entity.

Since your Collage class does not have a property named "com.data.Student" it causes your error.

You should consider refactoring your code a little bit. If you want the Collage to handle a list of Student entities, change List lstStudent to List<Student> lstStudent. Now, you can map the classes so that you tell Hibernate the relation between the 2 entities:

@Entity
class Collage {
    int id;
    String collageName;
    List<Student> lstStudent;
}

@Entity
class Student{
    String studentName;
    Collage collage;
    int id;
}

In the Collage class for the List<Student> lstStudent getter you will have:

@OneToMany(fetch = FetchType.LAZY, mappedBy = "collage")
public List<Student> getStudents() {
    return this.lstStudents;
}

, while in the Student class for the getter of Collage you will have:

@ManyToOne(fetch = FetchType.LAZY)
public Collage getCollage(){
    return this.collage;
}

This basically allows you to create a Criteria on the Collage class and have direct access with an alias to its list of Students:

cr.createAlias("lstStudent", "studentsAlias");