How to mapping with List<T> type?

Liujiamin · **Joined:** Sat Sep 08, 2007 10:23 pm **Posts:** 1

I have code like this:

Code:

    [Serializable()]
    public class Role : GenericDomain<Guid>
    {
        private string _Name;

        public virtual string Name
        {
            get { return _Name; }
            set { _Name = value; }
        }

        private string _Description;

        public virtual string Description
        {
            get { return _Description; }
            set { _Description = value; }
        }

        private List<FunctionModuleBase> _Modules;

        public virtual List<FunctionModuleBase> Modules
        {
            get { return _Modules; }
            set { _Modules= value; }
        }
    }

Mapping like this:

Code:

  <class name="SMSSystem.Domain.Role" table="T_Role">
    <id name="ID" type="Guid">
      <column name="U_UID" sql-type="uniqueidentifier" not-null="true" unique="true"/>
      <generator class="guid" />
    </id>
    <property name="Name" type="string">
      <column name="S_Name" sql-type="varchar" length="200"/>
    </property>
    <property name="Description" type="string">
      <column name="S_Description" sql-type="varchar" length="2000"/>
    </property>
    <bag name='FunctionModules' table='T_RoleFunction' cascade='all' lazy='true' inverse='true' generic='true'>
      <key column='U_RoleUID'/>
      <many-to-many class="SMSSystem.Domain.FunctionModuleBase" not-found="ignore" lazy="proxy">
        <column name="U_FunctionUID" sql-type="uniqueidentifier"/>
      </many-to-many>
    </bag>
  </class>

But, it throw a exception when get the entity:
NHibernate.MappingException: Invalid mapping information specified for type SMSSystem.Domain.Role, check your mapping file for property type mismatches

System.InvalidCastException: Can not cast type “NHibernate.Collection.Generic.PersistentGenericBag`1[SMSSystem.Domain.FunctionModuleBase]” to type“System.Collections.Generic.List`1[SMSSystem.Domain.FunctionModuleBase]”

If I change the entity use IList<T>

Code:

        private IList<FunctionModuleBase> _Modules;

        public virtual IList<FunctionModuleBase> Modules
        {
            get { return _Modules; }
            set { _Modules = value; }
        }

It works fine.
How can I mapping property use List<T> type?
Thanks

karlchu · **Posted:** Sun Sep 09, 2007 12:53 am

You cannot map to List<T>, it must be IList<T>. One way around that is to implement your own NHibernate.UserType.IUserCollectionType for the mapping.

hace_x · **Joined:** Thu Oct 26, 2006 4:45 am **Posts:** 39

You can define your private property in your class with a generic list:

Code:

private IList<FunctionModuleBase> _Modules = new List<FunctionModuleBase>(); 

        public virtual IList<FunctionModuleBase> Modules 
        { 
            get { return _Modules; } 
            set { _Modules= value; } 
        } 

If you want to have generic List from NHibernate for certain criteria, you can make a general method for it like this:

Code:

public static List<T> GetObjectList<T>(ICriteria criteria)
        {
            try
            {
                // Make results distinct
                criteria.SetResultTransformer(new NHibernate.Transform.DistinctRootEntityResultTransformer());

                List<T> objectList = new List<T>(criteria.List<T>());

                //And sort on default comparer 
                if (objectList is IComparable)
                {
                    objectList.Sort();
                }

                return objectList;
                
            }
            catch (HibernateException ex)
            {
                // Log the error to database for future
                // reference...
                return new List<T>(); // act as if we did not find anything
            }
   }

karlchu · **Posted:** Mon Sep 10, 2007 10:28 am

The reason one has to use an IList (which is an interface) instead of a List (which is a concrete class) is because NHibernate replaces the collection at run-time to facilitate lazy loading. The NHibernate-generated collection implements the IList interface but does not extend the List class. That explains the InvalidCastException.