I am migrating an old ASP application to a modern .NET version, to cut down on development times we are looking at the .NET 4.0 Entity Framework. However, we seem to have hit a brick wall in our development with this issue.
Given is a small part of our database: A table OBJECT which contains a list of cars and their respective properties. We also have a table OBJECT_OPTIONS which contains, for a given car in OBJECT, a list of OPTIONS, ACCESSORIES and STANDARD EQUIPMENT. These three types all have the same fields and are therefor stored in the same table. The column ncopt_type is used to discriminate between the different lists. Possible values are: 'opt', 'acc' and 'sta'. The table OBJECT_OPTIONS links to OBJECT via ncopt_obj_id which represents a unique car (obj_id) in table OBJECT.
Our goal is to provide the OBJECT entity with 3 properties that link to the different OBJECT_OPTIONS lists: - property OPTIONS - property ACCESSORIES - property STANDARDEQUIPMENT
We've tried different tutorials and walkthroughs concerning the table-per-hierarchy via inheritance model but haven't succeeded in creating a buildable model.
Technically what we did was:
- Create entity OBJECT
- Create entity OBJECT_OPTIONS, make it abstract
- Add entities OPTION, ACCESSORY and STANDARD_EQUIP all using basetype OBJECT_OPTIONS
- Add conditions to all three tables on ncopt_type = '...'
- Add 3 navigational properties to OBJECT, all linking to one of the inherited entities: OPTIONS, ACCESSORIES and STANDAARD_EQUIPMENT
A bunch of errors shows up during this setup, but we end up with this one:
Error 3032: Problem in mapping fragments starting at lines 250, 286:EntityTypes NCO.Model.OPTION, NCO.Model.ACCESSOIRE, NCO.Model.STANDAARD_EQUIP are being mapped to the same rows in table OBJECT_OPTIES. Mapping conditions can be used to distinguish the rows that these types are mapped to.
There is a condition present on all three objects though.
I have found no solution to this problem and have spent way too much time on it already. We are currently using a workaround method but would love to get this fixed as this situation will present itself a few more times by the end of the project.
Any help appreciated, if you need more information, please drop me a comment or an email.