NHibernate Duplicate class/entity mapping problem

Question

I've have started my foray into C#.NET and NHibernate and I'm finally stuck on an exception I can't seem to figure out, and Google isn't helping.

I'm getting a NHibernate.DuplicateMappingException : Duplicate class/entity mapping on my Parent class. Below is my mapping file for the Parent class, and the Youth class that uses the Parent class:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="Surrix.Cerberus.YouthData"
                   namespace="Surrix.Cerberus.YouthData.Domain">
  <class name="Parent">
    <id name="parentId">
      <generator class="guid" />
    </id>
    <property name="firstName" not-null="true" />
    <property name="lastName" not-null="true" />
    <property name="homePhone" />
    <property name="parentEmail" />
    <property name="relationshipToYouth" />

    <!-- Address component that should map to the Address class -->
    <component name="parentAddress">
      <property name="street" />
      <property name="state" />
      <property name="zipCode" />
      <property name="city" />
    </component>

  </class>

</hibernate-mapping>

And here is the relevant parts of the Youth class (it is considerably bigger)

<set name="YouthParents" table="YouthParents" cascade="none">
  <key column="youthId" />
  <many-to-many column="parentId" class="Parent"/>
</set>

Only other thing is the Youth class also has the firstName and lastName properties, but I can't see that being a problem.

Answer 1

As it gives a duplicate class entity mapping I can only imagen that you have two or more *.xml.hbm files referring to the same .net class.

Make sure that the xml class element for your Youth class does not have the same value for the name attribute.

Answer 2

You are adding the file or assembly containing the mapping twice to your Configuration object.

Answer 3

Make sure you are not doing both of these:

//Code Configuration
var cfg = new Configuration();
cfg.Configure();
cfg.AddAssembly(typeof(Employee).Assembly); 
// Presuming Employee resides in "MyAssembly" as seen below.

And then

//.config configuration
<session-factory>
     <!-- bunch of other stuff -->
    <mapping assembly="MyAssembly"/> <!-- as in MyAssembly.dll -->
</session-factory>