title: Entity Framework 1to1 relationship via association table not working in EDMX
body: <p>I have the following tables in SQL Server database
  <img src="https://i.stack.imgur.com/G3l5d.png" alt="enter image description here"></p>
  
  <p>Which has a 1-1 association table (FooBar) which has unique indexes on corresponding FooId, BarId, and the primary key is (FooId, BarId).</p>
  
  <p>To be clear FooBar does not allow any FooId (due to unique constraint) to be in the table more than once neither can any BarId (due to unique constraint) be in the table more than once. This is what makes it a 1-1 associative table.</p>
  
  <p>I want to have this association table instead of 1-1 relationship between Foo and Bar because in my real world scenario, Bar will have other relationships to different unrelated tables and I will want similar association tables (as opposed to adding new FK columns to Bar for each new table)</p>
  
  <p>Which I then bring these tables into my EDMX designer. The relationship is brought in as a Many to Many instead of One to One.
  <img src="https://i.stack.imgur.com/ewzVZ.png" alt="enter image description here"></p>
  
  <p>Which of course isn't what I want. I can manually change the model to a 1-1 relationship.
  <img src="https://i.stack.imgur.com/CQwBy.png" alt="enter image description here"></p>
  
  <p>But then I get an error (in the designer).
  <img src="https://i.stack.imgur.com/t2ooA.png" alt="enter image description here"></p>
  
  <p>Is this a bug or is it not possible to create a 1-1 association in this manner in EF?</p>