Is it possible to have the <id> in a mapping file be related to a unique string?



When I try this I receive a null reference exception.



My hibernate file is as follows:



<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">



<class name="WindowsApplication1.Sleeve, WindowsApplication1" table="tblReleaseDetails" lazy="true">



<!-- Doesn't work when column is an string -->

<!--

<id name="CatNumber" column="txtCatalogueNumber" access="nosetter.camelcase-underscore" unsaved-value="unknown-catalogue-number">

<generator class="increment"/>

</id>

-->



<!-- Works when column is an autonumber (integer) -->

<id name="Id" column="txtCatalogueNumber" access="nosetter.camelcase-underscore" unsaved-value="0">

<generator class="increment"/>

</id>





<property name="Label" column="txtRecordLabel"/>



etc. etc.

</class>



</hibernate-mapping>



In case this is significant – using NHibernate v1.0.2.0 and NHibernateContrib v1.0.2.0 to communicate with a Jet3.51 database using .Net 2.0



Cheers



Colin

It is probably has something to do with the database not letting you use a string as a primary key.

>It is probably has something to do with the database not letting you use
>a string as a primary key.

Hi.

Thanks for your thoughts.

The database (Access 97) has and does allow a string to be used as a primary key.

Any other ideas?

I'm not sure then. Maybe NHibernate does not allow id's to be of string type. What error are you getting when you try to run the code?

>What error are you getting when you try to run the code?

A null reference exception - despite the property to which the Id relates returning a string with a value in it.

Have you marked the property as virtual ?

>Have you marked the property as virtual ?

Oops! I hadn't.

However, when marking the property as virtual I am now receiving a different error message:

"Specified cast is not valid"

Any ideas?

Colin

Can you post your mapping file and entity class so I can have a look.

My class is as follows:

using System.Drawing;

namespace WindowsApplication1
{

public class Sleeve //: CoreBusinessObject
{
#region Fields

private Image _frontCover;
private int _id;

public virtual int Id
{
get { return _id; }
set { _id = value; }
}

#endregion

#region Constructors

public Sleeve()
: this(0, null)
{
}


public Sleeve(Image frontCover)
: this(0, frontCover)
{
}

public Sleeve(int identity, Image frontCover)
//: base(identity)
{
this.FrontCover = frontCover;
this.CatNumber = "catalogue-number-in-constructor";
}


public Sleeve(Sleeve sleeveToCopy)
//: this(sleeveToCopy.Id, sleeveToCopy.FrontCover)
{
}

#endregion

#region Properties

private string _catNumber;

public virtual string CatNumber
{
get { return "some-primary-key"; }
set { _catNumber = value; }
}
private string _label;

public string Label
{
get { return "record-label"; }
set { _label = value; }
}
private string _format;

public string Format
{
get { return ""; }
set { _format = value; }
}
private string _artist;

public string Artist
{
get { return ""; }
set { _artist = value; }
}
private string _title;

public string Title
{
get { return ""; }
set { _title = value; }
}
private short _value;

public short Value
{
get { return 0; }
set { _value = value; }
}
private string _condition;

public string Condition
{
get { return ""; }
set { _condition = value; }
}
private bool _forSale;

public bool ForSale
{
get { return true; }
set { _forSale = value; }
}



public virtual Image FrontCover
{
get
{
return _frontCover;
}

set
{
_frontCover = value;
}
}

#endregion

#region Methods


public override string ToString()
{
if (FrontCover != null)
{
return "<FrontCover=System.Drawing.Bitmap>";
}
else
{
return "<FrontCover=null>";
}
}

#endregion
}
}

and my hibernate mapping file is as follows:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">

<class name="WindowsApplication1.Sleeve, WindowsApplication1" table="tblReleaseDetails" lazy="true">

<!-- Doesn't work when column is an string -->
<!---->
<id name="CatNumber" column="txtCatalogueNumber" access="nosetter.camelcase-underscore" unsaved-value="unknown-catalogue-number">
<generator class="assigned"/>
</id>


<!-- Works when column is an autonumber (integer)
<id name="Id" column="txtCatalogueNumber" access="nosetter.camelcase-underscore" unsaved-value="0">
<generator class="increment"/>
</id>
-->


<property name="Label" column="txtRecordLabel"/>
<!--
<property name="Format" column="txtFormat"/>
<property name="Artist" column="txtArtist"/>
<property name="Title" column="txtTitle"/>
<property name="Value" column="txtCondition"/>
<property name="Condition" column="intValue"/>
<property name="ForSale" column="ynForSale"/>
-->

</class>

</hibernate-mapping>

try

Don't know if this is the problem. Se documentation "5.1.4.1. generator"

>try <generator class="uuid.string">

I have tried this and various others all to no avail.

FWIW I would have thought 'assigned' would have done the trick where I am assigning this within the business object - but it doesnt seem to like this either.

Regardless of what I provide a message "Specified cast is not valid" is displayed.