Querying two classes

rferj · **Joined:** Mon Feb 04, 2008 7:24 pm **Posts:** 6

Hi.

I am testing NHibernate as an option for the architecture of my systems. I created a project with two classes, made my mappings and I can query each one without problems. But I can't figure out how do I do a simple join between these two classes, though I have tried different ways as stated on the docs.

These are my two (simplified) classes:

Code:

'My main class, Persons
Public Class Persons

Private intId As Integer
Private strPerson As String

Public Overridable Property PersonId() As Integer 
        Get
            Return intId
        End Get
        Set(ByVal value As Integer)
            intId = value
        End Set
End Property

Public Overridable Property PersonName() As String
        Get
            Return strPerson
        End Get
        Set(ByVal value As String)
            strPerson = value
        End Set
End Property

End Class


'My associated class, Members
Public Class Members

Private intId As Integer
Private intPersonId As Integer
Private strStatus As String

Public Overridable Property MemberId() As Integer 
        Get
            Return intId
        End Get
        Set(ByVal value As Integer)
            intId = value
        End Set
End Property

Public Overridable Property PersonId() As Integer 
        Get
            Return intPersonId
        End Get
        Set(ByVal value As Integer)
            intPersonId = value
        End Set
End Property

Public Overridable Property MemberStatus() As String
        Get
            Return strStatus
        End Get
        Set(ByVal value As String)
            strStatus = value
        End Set
End Property

End Class

There are a one-to-one relationship between these two classes. On the database side, the members table has a FK to the Persons table on the PersonId column. I need a method that lists the {Persons}.PersonId and the associated {Members}.Status. Do I need to create a third class that contains this method? Where should I put the mapping for this association?

TIA,
rferj

jta · **Posted:** Wed Mar 12, 2008 1:06 pm

You can map the Member onto the Person class based on the relationsship so you can Access:

Person.Member.MemberStatus

you can use this in your queries as well.

Take a look at 5.1.11 in the nHibernate reference manual

rferj · **Joined:** Mon Feb 04, 2008 7:24 pm **Posts:** 6

Hi jta !

I read the topic, but I should have misunderstood something. On my Persons class I defined a new property called Users, that I want to list the join between Persons and Members:

Code:

Public Overridable Property Users() As IList
    Get
        Return lstUsers
    End Get
    Set(ByVal value As IList)
        lstUsers = value
    End Set
End Property

And I changed the mapping file of my Persons class as below:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="TestHB" assembly="TestHB">
<class name="Persons" table="tblPersons" lazy="true">

<id name="PersonId" column="PersonId" type="Int32">
<generator class="native">
<param name="sequence">Persons_seq</param>
</generator>
</id>

<property name="PersonName" type="String" length="150" not-null="true" />

<one-to-one name="Users" class="Members" constrained="true" property-ref="PersonId" />
</class>

When I run the application, I receive errors saying that my property is invalid. Can you see where is the error? I tried some changes on the one-to-one element but could not solve this.

TIA,
rferj

wolli · **Posted:** Thu Mar 13, 2008 3:05 am

An one-to-one association expects a single value not a list. If you really have a one-to-one relation you have to use

Code:

Public Overridable Property Users() As Members
    Get 
        Return users 
    End Get 
    Set(ByVal value As Members) 
        users = value 
    End Set 
End Property

or you have to map a collection

Code:

<bag name="Users" table="tblMembers">
    <key column="PersonId" />
    <one-to-many class="Members" not-found="ignore" />
</bag>