.UniqueResult() returns multiple object due to inheritance

jaded · **Posted:** Wed Nov 02, 2005 10:12 am

I have a query which should return only one row:
repository.Session.CreateCriteria(typeof(Employee)).
Add(NHibernate.Expression.Expression.Eq("ID", NBNo)).UniqueResult();

ID is not the primary key on the table but is unique. I am expecting to return a employee class, however I get three other empty objects back + 1 the one I requested.
all the other objects inherits from employee which I believe causes the problem.

How can i get around this ?

KPixel · **Posted:** Thu Nov 03, 2005 10:55 am

How do you get three other empty objects back + 1 the one I requested?
UniqueResult() returns an object which should be the one you requested...

Are these other objects matching the criteria (ID=NBNo)?

jaded · **Posted:** Fri Nov 04, 2005 2:32 am

yep they match the critieria. however it does not match the exact type. it matched the baseclass of the 3 objects type on the subclass's type

marcal · **Posted:** Thu Nov 10, 2005 2:29 pm

I'm still wondering how you get 4 objects out of a method that returns only one. I'm thinking the answer to the question lay somewhere in that problem.

k-dub · **Joined:** Thu May 12, 2005 8:45 am **Posts:** 226

jaded wrote:

ID is not the primary key on the table but is unique.

How is this uniqueness defined? If you are getting four records with the same ID, it must not be unique as NHibernate defines it. I'm not sure about how .UniqueResult() behaves, but it sounds to me like uniqueness is also related to type and/or primary key. What kind of inheritance model are you using?

Jaded · **Posted:** Mon Nov 14, 2005 12:50 pm

This is the mapping that i am using. Note that both planner and employee maps to the exact same table.

by using this function:

Code:

public T GetObjectByUniqueKey<T>(string field, string value)
   {
      
      return  (T)Session.CreateCriteria(typeof(T)).
            Add(NHibernate.Expression.Expression.Eq(field, value)).UniqueResult();
   }

and passing in e.g. 'planner' as the type i get null back because multiple records was returned??

to 'fix this problem i do the following:

Code:

static public T LookUpByEmployeeNBNo<T>(object NBNo)
      {
         //HACK: problem with nhibernate returning all subclasses on list
          
         if (NBNo == null) return default(T);
         IList employees = repository.Session.CreateCriteria(typeof(T)).
            Add(NHibernate.Expression.Expression.Eq("NBNo", NBNo)).List();
            if (employees.Count > 0)
            {
                foreach (object obj in employees)
                    if (obj.GetType() == typeof(T)) return (T)obj;
            }
          
         return default(T);

         
      }

looking at the Ilist result i look for an exact match of the type 'Planner' and then return that object

Key point is that planner inherits from employee however a employee is not a planner therefore only a planner should be returned!!

please help if any got an answer thanks!

Code:

<class name="Planner" table="Employee">
      <id name="ID" column="ID">
         <generator class="assigned" />
      </id>
      <property column="status" name="_status"></property>
      <many-to-one name="Branch" column="BranchID" class="Branch" />
      <property name="SurName" column="SurName" type="String" />
      <property name="NBNo" column="NBNo" type="String"/>
      <set name="Roles" cascade="all" >
         <key column="EmpId"/>
         <one-to-many class="EmployeeRole"/>
      </set>

   </class>


<!-- Employee -->
   <class name="Employee" table="Employee">
      <id name="ID" column="ID">
         <generator class="assigned" />
      </id>
      <property column="status" name="_status"></property>
      <many-to-one name="Branch" column="BranchID" class="Branch" />
      <property name="SurName" column="SurName" type="String" />
      <property name="NBNo" column="NBNo" type="String"/>
      <set name="Roles" cascade="all" >
         <key column="EmpId"/>
         <one-to-many class="EmployeeRole"/>
      </set>
      
   </class>

k-dub · **Joined:** Thu May 12, 2005 8:45 am **Posts:** 226

If you are using one table, I suspect you need a discriminator column. http://nhibernate.sourceforge.net/nh-docs/html/mapping.html#mapping-declaration-discriminator