NHibernate many to many mapping error - NHibernate.MappingException: Could not determine type for:

Question

I am having a problem when trying create a many to many mapping. Consider the following tables:

CREATE TABLE [dbo].[student]
(
    [Id]            INT             IDENTITY (1, 1) NOT NULL,
    [Name]          NVARCHAR(255)   NOT NULL,
    -- Some other stuff...      
)

CREATE TABLE [dbo].[Subject]
(
    [Id]            INT             IDENTITY (1, 1) NOT NULL,
    [Name]  NVARCHAR (50)   NOT NULL,

    -- Some other stuff...
)

CREATE TABLE [dbo].[studentToSubject]
(
    [studentId] INT NOT NULL,
    [subjectId]     INT NOT NULL,
)

The interesting part of my student mapping file looks like this:

<id name="Id" type="Int32">
      <column name="Id" sql-type="int" not-null="true" unique="true"/>
      <generator class="native" />
    </id>

      <property name="Name" not-null="true" />
      <bag name="subjects" table="studentToSubject">
          <key column="studentId"></key>
          <many-to-many column="subjectId" class="subject" />
      </bag>

I want to end up with a student with a collection of their subjects. However, I get an error:

NHibernate.MappingException: Could not determine type for: MyApp.Domain.Subject, MyApp.Domain, Version=1.0.0.0, Culture=neutral, PublicKeyToken=865c2d2b185d0c4b, for columns: NHibernate.Mapping.Column(studentId).

I have seen some examples of this type of mapping, but they differ in the fact that their Id columns have name that match the mapping table name, for example their Id column in the student table is called 'studentId'. I cannot do this (it has to be Id) but I think this is the cause of the problem.

Thanks

The error is talking about a NotificationType which I don't see in your mapping. Either you're missing an important part of the student mapping or the problem is in another mapping. — Shane Courtrille
– Shane Courtrille, Commented Mar 4, 2010 at 16:00
Please post the mapping of your subject class, so i can check the answer i've given for validity :) — F.B. ten Kate
– F.B. ten Kate, Commented Aug 13, 2011 at 15:42

fatemeh · Accepted Answer · 2011-08-17 10:09:15Z

1

you should write this relation for subject class again and sure your field for relation is correct.

i do it with attribute models

answered Aug 17, 2011 at 10:09

fatemeh

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Comments

Shane Courtrille · Accepted Answer · 2010-03-04 16:22:55Z

0

It seems like you are either missing the mapping file for Subject (did you remember to include it properly?) or you need to provide the full path if it is in a different namespace.

answered Mar 4, 2010 at 16:22

Shane Courtrille

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Comments

Will Marcouiller · Accepted Answer · 2010-03-05 03:39:09Z

Please correct me if I'm wrong, but I guess there's something messy about your Id mapping. Perhaps it can be done the way you do and I have never seen it, this is possible.

Though I would write my mapping like so:

<class name="Student"> <!-- I omit the table attribute as both your class and table seems to have the same name. -->
  <id name="Id">
    <generator class="native"/> <!-- Though I would recommend using "identity" if SQL Server's used. -->
  </id>

  <property name="Name" length="255" not-null="true"/>

  <list name="Subjects" not-null="true" table="StudentToSubject">
    <key column="studentId" />
    <many-to-many column="studentId" class="Subject" />
  </list>
</class>

Within the element, it is optional to specify the not-null, unique, type and sql-type attributes as NHibernate will determine them during runtime using reflection, though I understand that for pedagogy purposes, it is better to write those. Plus, if you want your Id property name within your object class be the same as your table field, you may just omit the column attribute. NH will then consider using the same name as the property for the data table field Id field.

As for your collection of subjects, if you intend to use a Dictionary in your Sudent class, you'd better the element instead of . However, if you want a List, you'd better opt for the element as I did. This all depends on your needs and your objective through this exercise.

Please, consider that I took this NH XML mapping right from the top of my head, and I didn't test it, so it might contain errors on fly.

In addition to this, you can take an eye out on this: Chapter 6. Collection Mapping

Hope this helps! =)

Adam · Accepted Answer · 2010-03-05 14:14:36Z

0

Did you remember to set the .hbm.xml mapping files to an Embedded Resource? Also this line is not correct.

<many-to-many column="subjectId" class="subject" />

Subject should be capital S and it is good practice to give the namespace and assembly. such as <many-to-many column="subjectId" class="MyApp.Domain.Subject, MyApp.Domain" />

edited Mar 5, 2010 at 14:14

answered Mar 5, 2010 at 3:07

Adam

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Comments

F.B. ten Kate · Accepted Answer · 2011-08-13 15:41:24Z

0

I might be mistaken but the error hints at it:

NHibernate.MappingException: Could not determine type for: MyApp.Domain.Subject, MyApp.Domain, Version=1.0.0.0, Culture=neutral, PublicKeyToken=865c2d2b185d0c4b, for columns: NHibernate.Mapping.Column(studentId).

Basically the way i read the error, NHibernate can't figure out what type the column studentId is, The fault is most likely in your Subject mapping. There is a property there which apperently references a student (i'm guesing the other side of the many-to-many).

answered Aug 13, 2011 at 15:41

F.B. ten Kate

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