title: Select two lists as one list in ASP.NET Core linq
body: <p>I am trying to create a query with ASP.NET Core EF Core and Linq that would give me a List of users based on two different lists, something like this:</p>
  
  <pre><code>return await _context.Users
              .Include(u =&gt; u.PropertyOwners)
                  .ThenInclude(po =&gt; po.Property)
                      .ThenInclude(p =&gt; p.PropertyTenantLeases)
              .Include(u =&gt; u.PropertyOwners)
                  .ThenInclude(po =&gt; po.Owner)
              .Where(u =&gt; u.Id == userID)
              .Select(u =&gt; new List&lt;User&gt;() 
              { 
                  u.PropertyTenantLeases.Select(ptl =&gt; ptl.Tenant).ToList()
                  u.PropertyOwners.Select(po =&gt; po.Owner).ToList() 
              }).FirstOrDefaultAsync();
  </code></pre>
  
  <p>The tables that are used in this query are connected in the following way:
  <a href="https://i.stack.imgur.com/AoBSd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AoBSd.png" alt="Table design"></a>
  Everything is fine with this query except for the Select, with the Select I am trying to achieve that it returns a list of all the tenants in the PropertyTenantLeases table which is a junction table togheter with all the Owners form the PropertyOwners junction table (both Tenant and Owner are IdentityUser classes. When I right this query like this I get the following error:</p>
  
  <pre><code>The best overloeaded Add method 'List&lt;User&gt;.Add(User)' for the collection initializer has some invalid arguments
  </code></pre>
  
  <p>and also</p>
  
  <pre><code>Argument 1: cannot convert from 'System.Collections.Generic.List&lt;RosyMasterDBManagement.Models.User&gt;' to 'RosyMasterDBManagement.Models.User'
  </code></pre>