CODEWITHSUNDEEP
c#nhibernatenhibernate-mappingsubclass
Maxim Gershkovich
Maxim Gershkovich

Reputation: 47149

Subclass table mapping in nHibernate

Firstly, sorry about the wall of text.

I have the following schema. Note that User_Contact may contain a null in ContactID.

Schema

At the class level it is then implemented in the following way 

public abstract class User : EntityBase<Guid>, IAggregateRoot
{
    public User()
    {

    }

    public virtual string FirstName { get; set; }
    public virtual string LastName { get; set; }

    protected abstract override void Validate();
}

public class SiteUser : User
{
    public SiteUser() { }

    public virtual Guid ApplicationId { get; set; }
    public virtual string UserName { get; set; }
    public virtual string LoweredUserName { get; set; }
    public virtual string MobileAlias { get; set; }
    public virtual bool IsAnonymous { get; set; }
    public virtual DateTime LastActivityDate { get; set; }

    protected override void Validate()
    { 
        if (this.ApplicationId == Guid.Empty)
            base.AddBrokenRule(UserBusinessRules.ApplicationIdRequired);

        if (this.UserName.IsNullOrEmpty())
            base.AddBrokenRule(UserBusinessRules.UserNameRequired);

        if (this.LoweredUserName.IsNullOrEmpty())
            base.AddBrokenRule(UserBusinessRules.LoweredUserNameRequired);

        if (this.LastActivityDate == DateTime.MinValue)
            base.AddBrokenRule(UserBusinessRules.LastActivityDateRequired);

    }
}

public class SiteContact : SiteUser
{

    public SiteContact() 
    {
    }


    public virtual int ExternalID { get; set; }
    //All the rest...

    protected override void Validate()
    { 
        //validate
    }
}

So basically the idea is that every single SiteContact is a SiteUser but not every SiteUser is a SiteContact.

Where I have gotten completely stuck is how on earth to map this relationship in nHibernate. I seem to be able to retrieve a SiteUser but unable to retrieve a SiteContact and it is clear why. The mapping that I have implemented results in the following sql being executed.

SELECT this_.userid             AS UserId18_0_, 
       this_.firstname          AS FirstName18_0_, 
       this_.lastname           AS LastName18_0_, 
       //Blah blah.....
FROM   user_contact this_ 
       INNER JOIN contact this_1_ 
               ON this_.userid = this_1_.contactid  //Here is the error this should be ContactID = ContactID
       INNER JOIN aspnet_users this_2_ 
               ON this_.userid = this_2_.userid 
WHERE  ( CASE 
           WHEN this_.contactid IS NOT NULL THEN 1 
           ELSE 0 
         END ) = '1'

But I can't for the life of me work out how to fix this problem in my hbm mapping file. Here is the file with some fields omitted for simplicity. 

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="MyProject.Namespaces.Model.Entities" assembly="MyProject.Namespaces.Model">


  <class name="User" table="User_Contact" lazy="true" abstract="true">

    <id name="ID" column="UserId" type="guid">
      <generator class="guid" />
    </id>

    <discriminator column="ContactID" formula="(CASE WHEN ContactID IS NOT NULL THEN 1 ELSE 0 END)" />

    <property name="FirstName">
      <column name="FirstName" sql-type="nvarchar(500)" not-null="true" />
    </property>

    <property name="LastName">
      <column name="LastName" sql-type="nvarchar(500)" not-null="true" />
    </property>

    <subclass name="SiteContact" discriminator-value="1">
      <join table="Contact">
        <key column="ContactID" /> //I assume the problem is here. I have tried adding foreign-key="ContactID" to no success

        <property name="ExternalID" insert="false" update="false">
          <column name="ExternalID" sql-type="int" not-null="true" />
        </property>

        //The rest of the mapped columns

      </join>
      <join table="aspnet_Users">
        <key column="UserId" />

        <property name="ApplicationId">
          <column name="ApplicationId" sql-type="guid" not-null="true" />
        </property>

        <property name="UserName">
          <column name="UserName" sql-type="nvarchar(256)" not-null="true" />
        </property>

        <property name="LoweredUserName">
          <column name="LoweredUserName" sql-type="nvarchar(256)" not-null="true" />
        </property>

        <property name="MobileAlias">
          <column name="MobileAlias" sql-type="nvarchar(16)" not-null="false" />
        </property>

        <property name="IsAnonymous">
          <column name="IsAnonymous" sql-type="bit" not-null="true" />
        </property>

        <property name="LastActivityDate">
          <column name="LastActivityDate" sql-type="datetime" not-null="true" />
        </property>

      </join>
    </subclass>

    <subclass name="SiteUser" discriminator-value="0">
      <join table="aspnet_Users">
        <key column="UserId" />

        //blah blah blah

      </join>
    </subclass>

  </class>

</hibernate-mapping>

Hopefully someone could please tell me if I am even on the right track about this mapping and perhaps provide some guidance?

Upvotes: 1

Views: 2421

Answers (1)

Martin Ernst
Martin Ernst

Reputation: 5679

This seems like a pretty convoluted way of mapping it. I'm not sure what benefits you're hoping to achieve from using inheritence in this situation, and I would suggest using composition instead (ie. having a class per table and mapping the relationships).

Having said that, you presumably have your reasons, so I would suggest the following to achieve what I think you want:

  1. Map your SiteUser class as the base class and use a join from User_Contact to aspnet_Users (so don't have User as the base in the mapping)
  2. Map your SiteContact then as a subclass using the joined-subclass mapping instead of the subclass so you don't need to use discriminators.

Upvotes: 1

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