问题
We are learning Entity Framework 6.1 (from NuGet) as we move away from Linq2Sql. We have a small handful of tables that associate two separate tables like shown below.
EF6 Database First generation
DB Diagram:
Schema Overview:
When in Visual studios, blank class library, doing a Database First EF6 EDMX file, the diagram only generates TableA and TableC -- the TableB does not get generated.
Visual Studios View:
You can see that only TableA and TableC are created. Technically TableB should have been created, because you would want to be able to manage those references.
The Association between A and C shown in the diagram:
I feel like I am missing an option, or misunderstanding a key concept of Entity Framework. Any idea how to have the missing TableB generated with the T4? The EDMX file does show it, but for some reason it doesn't get generated into a .CS file with the two properties indicating the relationship.
The primary reason we need this, is we extended the EF6 T4 template to add some factory patterns to match our existing models. Because it doesnt generate a class for TableB, we dont get the autogenerated code that we are looking for.
Thoughts / suggestions? Thanks.
回答1:
Weak entities or join tables will not be generated by EF, you need to configure the relationships manually thru fluent API or using data annotations
As stated on Microsoft's website: under Relationship's convention:
Note: If you have multiple relationships between the same types (for example, suppose you define the
PersonandBookclasses, where thePersonclass contains theReviewedBooksandAuthoredBooksnavigation properties and theBookclass contains theAuthorandReviewernavigation properties) you need to manually configure the relationships by using Data Annotations or the fluent API. For more information, see Data Annotations - Relationships and Fluent API - Relationships.
Refer to this link for more information
UPDATED
A workaround will work in case of EDMX ( but it cost maintenance) as follows:
- Remove the foreign keys from the join table in the database
- Update the EDMX from database
- Recreate the foreign keys in the join table
this workaround will work as long as you will not update your Model from the database again.
Recommended solution, keep everything as it was generated by EDMX and learn more about how to use crud operation for this case using the following links that were reported "helpful" by the user '@TravisWhidden'
- Insert/Update Many to Many Entity Framework . How do I do it?
- https://www.youtube.com/watch?v=uMQwORSTGX4 ( video)
回答2:
As mentioned by @Hadi Hassan, EF will not “Expose” or recognize Relational Tables that are composed exclusively of other Entities.
Work Around:
If you only need to ‘READ’ the data you can
- Define a
viewin your Schema forTableB. - Then do a
Model (.EDMX)Update from DB (select the Update Views) - You will now be able to query your
TableBdata using your EF Context.
If you need to modify (Create,Update,Destroy) records in your TableB
Create Stored Procedures in your Schema, accordingly.
Import your Procs as Function into Your EF Model
You can now call those Functions from your model Context for the rest of your CRUD operations.
回答3:
The easiest way I've found around this is to add an autoincrement field to the table and make this sole field the primary key. Then add a unique constraint consisting of the two foreign keys. You might need to drop the table and recreate it in order to set it up this way because the database will not like dropping the existing PK relationships.
Then in the Entity model delete the table and also any navigation properties Entity may have created related to the relationships in this table. Save your model, rebuild, and then update From Database in the diagram. Your table should now appear to Entity as a regular table.
来源：https://stackoverflow.com/questions/31526066/entity-framework-6-missing-table-with-only-primary-keys-referencing-different