title: The nested query is not supported. Operation1='UnionAll' Operation2='MultiStreamNest'
body: <p>I have a Linq to Entities query of the following form:</p>
  
  <pre><code>var x = from a in SomeData
      where ... some conditions ...
      select new MyType
      {
          Property = a.Property,
          ChildCollection = from b in a.Children
                          select new MyChildType
                          {
                              SomeProperty = b.Property,
                              AnotherProperty = b.AnotherProperty
                          }
      };
  
  var y = from a in SomeData
      where ... some other conditions ...
      select new MyType
      {
          Property = a.Property,
          ChildCollection = from b in a.Children
                          select new MyChildType
                          {
                              SomeProperty = b.Property,
                              AnotherProperty = b.AnotherProperty
                          }
      };
  
  var results = x.Concat(y);
  </code></pre>
  
  <p>(This is a simplified example - the 'where' and 'select' clauses are more complex than shown here.  I'm using separate queries statements as creating a single combined one is just too complicated, has too many conditionals and takes an age to compile)</p>
  
  <p>Compiles fine, but fails at execution with the exception:</p>
  
  <pre><code>"The nested query is not supported. Operation1='UnionAll' Operation2='MultiStreamNest'
  </code></pre>
  
  <p>Note, I am trying to project into a nested typed structure.  If I call .ToList() on x and y prior to the Concat() it works fine.  As a further point, one of my properties is an enum, but I am assigning to it using an integer wrapper property.</p>
  
  <p>Is there a way I can do what I want to do without having to pull all the data into memory?  Or is it the enum causing the failure?</p>
  
  <p>Thanks,</p>
  
  <p>T</p>