EF4: Creating a 0..1 to Many Association

Question

I am trying to add an association that I didn't have originally. I realized that two tables were technically related, and that some navigation properties might simplify what I would have otherwise had to do manually. The tables and their keys look like this:

Import
Primary Key:
   Number : Int32
   Date : DateTime

Hour
Primary Key:
   DepartmentID : Int32
   UserNumber : Int32
   Date : DateTime

The association is named ImportHour. Import.Number maps to Hour.UserNumber, and Import.Date maps to Hour.Date. I am trying to add an association that is 0..1 on Import, and * on Hour with navigation properties and no additional foreign keys. When I do this, the designer tells me that the association is not mapped. If I then generate the DDL, it creates new fields Hours.Import_Date and Hours.Import_Number (Hours is the actual database table name for the Hour entity). If I manually map the fields, I end up with the following error:

Error 3021: Problem in mapping fragments starting at line 332:
Each of the following columns in table Hours is mapped to multiple conceptual side properties:
Hours.Date is mapped to <ImportHour.Hour.Date, ImportHour.Import.Date>
Hours.UserNumber is mapped to <ImportHour.Hour.UserNumber, ImportHour.Import.Number>*

I am not really sure what is happening, and I don't think I understand the 'mapping' process well enough to figure this out. It almost seems as if it wants a quintuple key, instead of realizing that the one key maps to the other. I look at my other one-to-many associations, and they do not even have table mappings; I think they have referential constraints instead, but you obviously can't have a referential constraint with a 0..1 to many association.

Answer 1

As far as I can tell from other databases I have since used, the issue here seems to be that the EF model requires a foreign key to already exist in the database. While I cannot seem to get EF to generate one, it will accept one if it already exists. (Contrary to what I said in the question, you can have a referential constraint on a 0..1 to many (nullable) foreign key).