title: How do I correctly set an association between two objects in the Entity Framework 4 Entitydesigner?
body: <p>For a new project I'm trying to create my business classes first and create the real database tables later. Therefore I'm using the Entity Framework 4 Designer. A created a new "ADO.Net Entity Data model" file, with the extension .edmx.</p>
  
  <p>I created two Entities:<br>
  <img src="https://i.stack.imgur.com/w65e1.png" alt="alt text"></p>
  
  <p>I want to add a 1 to nc relation between Product -> Group. If I'd created the MSSQL database first, I would have added a column IDGroup to the Table Product and referenced Product.IDGroup to Group.IDGroup. As far as I can see, I can't add such association in the designer if I add a new Property called IDGroup to the Product Entity</p>
  
  <p>This is how I add the mapping:
  <img src="https://i.stack.imgur.com/dcPvl.png" alt="alt text"></p>
  
  <p>Which results in:<br>
  <img src="https://i.stack.imgur.com/JQ8WB.png" alt="alt text"></p>
  
  <p>Now the part what this question is about: If I add two tables from an existing MSSQL database to the edmx file, I'll get the compile error:</p>
  
  <pre><code>Error 3027: No mapping specified for the following EntitySet/AssociationSet - GroupSet, ProductSet
  </code></pre>
  
  <p>What does that error mean and what must I do to fix this?
  If I delete those two tables, I'll receive a warning instead:</p>
  
  <pre><code>Error 2062: No mapping specified for instances of the EntitySet and AssociationSet in the EntityContainer myContainer.
  </code></pre>
  
  <p>Something tells me, I'm doing this all wrong and this is just basic stuff. How can I do it right?</p>