Column not found, message from server: "Unknown column 'type' in
'field list'"

You may get this error if you add a many-to-one relationship to a
class, and forget to add the corresponding column to the corresponding
table.  For example, if you have a table like this:

create table cd (
  id integer primary key,
  title varchar(255)
);

and a class CD:

public class CD {
  protected int id;
  protected String title;
}

with a Hibernate mapping document:

<class name="eg.CD" table="cd">

  <id name="id"><generator class="native"/></id>
  
  <property name="title"/>

</class>

then, if you add a property to the class and mapping document:

public class CD {
  protected int id;
  protected String title;
  protected Colour colour;
}

<class name="eg.CD" table="cd">

  <id name="id"><generator class="native"/></id>
  
  <property name="title"/>
  <many-to-one name="colour" class="eg.Colour"/>

</class>

then you will get an error message something like the above unless you
remember to add a column to the table cd:

create table cd (
  id integer primary key,
  title varchar(255),
  colour_ref integer
);

create table colour (
  id integer primary key,
  name varchar(255)
); 

"Collections may not contain other collections."
		-- http://www.hibernate.org/hib_docs/reference/en/html/collections.html#collections-persistent