Nhibernate mapping a class which has a generic list property

Question

I am new to Nhibernate and I am trying to map a class (Invoice) which has a generic list property using Nhibernate but I keep getting error: "An association from the table InvoiceDetails refers to an unmapped class: System.Int32". Because each invoice has more details I have tought of one to many relation between Invoices and InvoiceDetails table.

Details: a) Invoice class:

public class Invoice
{
    private IList<InvoiceDetail> _invoiceDetails = new List<InvoiceDetail>();

    public virtual int InvoiceID { get; set; }
    public virtual string SerialNumber { get; set; }
    public virtual string Number { get; set; }
    public virtual DateTime InvoiceDate { get; set; }
    public virtual decimal Amount { get; set; }
    public virtual IList<InvoiceDetail> InvoiceDetails
    {
        get { return _invoiceDetails; }
        set { _invoiceDetails = value; }
    }
    public virtual Customer customer { get; set; }
    public virtual Institution Institution { get; set; }
    public virtual Receipt receipt { get; set; }
    public virtual bool IsDeleted { get; set; }
}

b) InvoiceDetail class:

public class InvoiceDetail
{
    public virtual int InvoiceDetailID { get; set; }
    public virtual int InvoiceID { get; set; }
    public virtual string ServiceDescription { get; set; }
    public virtual string Unit { get; set; }
    public virtual int Quantity { get; set; }
    public virtual double Value { get; set; }
    public virtual bool IsDeleted { get; set; }
}

c) Invoice mapping file:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
    assembly="MyProject" namespace="MyProject.Model">
    <class name="Invoice" table="Invoices">
        <id name="InvoiceID" column="InvoiceID" type="int">
            <generator class="native"></generator>
        </id>
        <property name="SerialNumber" column ="InvoiceSerialNumber"/>
        <property name="Number" column ="InvoiceNumber"/>
        <property name="InvoiceDate"/>
        <property name="Amount"/>
        <property name="IsDeleted" />
        <many-to-one name="Institution" column="InstitutionID" />
        <bag name="InvoiceDetails" access="nosetter.camelcase"
            inverse ="true" lazy ="false" cascade="all-delete-orphan">
            <key column="InvoiceID"/>
            <many-to-one class="MyProject.Model.InvoiceDetail, MyProject"/>
        </bag>
    </class>
</hibernate-mapping>

d) InvoiceDetail mapping file:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
    assembly="MyProject" namespace="MyProject.Model">
    <class name="InvoiceDetail" table="InvoiceDetails">
        <id name="InvoiceDetailID" column="InvoiceDetailID" type="int">
            <generator class="native"></generator>
         </id>
         <many-to-one name="InvoiceID" column="InvoiceID" />
         <property name="ServiceDescription"/>
         <property name="Unit"/>
         <property name="Quantity"/>
         <property name="Value"/>
         <property name="IsDeleted" />    
     </class>
 </hibernate-mapping>

Answer 1

Looks pretty good!

Fix InvoiceID

You need to fix the InvoiceDetail.InvoiceID property. With many-to-one properties, you should model them as references to the parent entity instead of just as simple value properties containing an ID. You got it right with Invoice.Institution .

In InvoiceDetail , replace this...

public virtual int InvoiceID { get; set; }

... with this:

public virtual Invoice Invoice { get; set; }

Likewise, in your mappings, replace this...

<many-to-one name="InvoiceID" column="InvoiceID" />

... with this:

<many-to-one name="Invoice" column="InvoiceID" />

Fix Bag

Also, a bag cannot be many-to-one - it should be one-to-many. See the Documentation . Replace this...

<bag name="InvoiceDetails" access="nosetter.camelcase" inverse ="true" lazy ="false" cascade="all-delete-orphan">
  <key column="InvoiceID"/>
  <many-to-one class="MyProject.Model.InvoiceDetail, MyProject"/>
</bag>

... with this:

<bag name="InvoiceDetails" access="nosetter.camelcase" inverse ="true" lazy ="false" cascade="all-delete-orphan">
  <key column="InvoiceID"/>
  <one-to-many class="MyProject.Model.InvoiceDetail, MyProject"/>
</bag>

Caution about Lazy=False

One final note: be careful with lazy="false". If you are intending to improve performance be having NHibernate eagerly fetch those related records, this is not the way to do it. See http://ayende.com/blog/4573/nhibernate-is-lazy-just-live-with-it for an explanation of why this is a problem. Refer to http://nhibernate.info/doc/nh/en/index.html#performance-fetching for the various way to implement this correctly.