One exception you may run across while using Fluent Nhibernate (or straight up NHibernate) is System.Data.SqlClient.SqlException: Invalid column name ‘……’.  This is normally caused because you did not provide the correct column name when doing your mapping.

Lets take a look at the code below which is trying to map a many-to-one relationship to another entity.

References( x => x.BusinessUnit )
        .Access.AsCamelCaseField( Prefix.Underscore )                
        .WithForeignKey( "DATASET_ID" )
	.FetchType.Join

As you can see from the code we  are trying to setup the mapping to our BusinessUnit entity, and we are providing the foreign key as ‘DataSet_ID’.  However when we generate the .hbm.xml file and run the code it throws the Invalid Column name exception saying that it cannot find BusinesUnit_ID. 

Here is the .hml.xml snippet for this mapping

<many-to-one access="field.camelcase-underscore" foreign-key="DATASET_ID" fetch="join" name="BusinessUnit" column="BusinessUnit_id" />

At first glance you may be wondering why it is trying to use BusinessUnit_ID as the column name.  The reason is that FluentNHibernate assumes that the column u are mapping against in the patent is the ‘id’ value of the entity (BusinessUnit_ID).  However, in my case this is not true.  In order to resolve this I simply need to tell FluentNHiberhate what the true column name is.  I can do so with the following code

References( x => x.BusinessUnit )
        .Access.AsCamelCaseField( Prefix.Underscore )                
        .WithForeignKey( "DATASET_ID" )
	.TheColumnNameIs( "DATASET_ID" )
	.FetchType.Join

When I run this code, it will generate the following .hbm.xml file

<many-to-one access="field.camelcase-underscore" foreign-key="DATASET_ID" fetch="join" name="BusinessUnit" column="DataSet_ID" />

So, if you ever find you self with the Invalid column name exception make sure you have completely setup your mappings.

Till next time,