nhibernate mapping another vigilant id

ok, nhibernate doubt here. i have twin objects i map any other. i have "vendor" "township" ... twin should related zip code, id. i have finished times btw objects controlling id's nonetheless never something this.

the emanate i am carrying zipcodes while stored strings somehow being incited integers (leading 0 being dropped)? presumably controlling id objects.

here error:

server blunder '/hqwebsite' application.
no quarrel given identifier exists[hqdata.objects.township#7922]

it's also information database i looked there good information accurate.

here i mapped businessman xml file:

<many-to-one name="_township" column="zipcode" foreign-key="zipcode" class="hqdata.objects.township, hqdata" />

here ability municipality one:

   <set name="_vendors" cascade="all">
      <key  column="zipcode" foreign-key="zipcode"/>
      <one-to-many 
         class="hqdata.objects.vendor, hqdata"/>
    </set>

is anyone informed nhibernate finished before? thanks!