Flatten/expand columns of Navigation Property for ViewModel?

Question

Say I have an Employee entity, and each Employee has many EmployeeChange entities.

An Employee and EmployeeChange looks like:

class Employee
{
  [Key]
  public int EmployeeKey {get;set;}

  public string EmployeeName { get; set; }

  public int CurrentEmployeeChangeKey { get; set; }
  [ForeignKey("CurrentEmployeeChangeKey")]    
  public virtual EmployeeChange CurrentEmployeeChange { 
    get { return EmployeeChanges.FirstOrDefault() ; } /*set;*/ }

  public virtual ICollection<EmployeeChange> EmployeeChanges { get; set; }    
}

class EmployeeChange
{
   [Key]
   public int EmployeeChangeKey { get; set; }

   public int EmployeeKey { get; set; }
   [ForeignKey("EmployeeKey")]       
   public virtual Employee Employee { get; set; }


   public string EmployeeStreet { get; set; }
   public string EmployeeCity { get; set; }
   public string Etc { get; set; }

   public DateTime ChangeEffective { get; set; }

}

Is there a LINQ query that can flatten these to make something like the below for us in a MVC ViewModel, without listing every single property? I.e. If I add/remove properties in my Entity or Entity class, I want the LINQ query to not have to change. The below of course is dynamically generated from a projection in the LINQ query rather than being an actually declared class. One important thing is any DataAnnotations will need to be preserved so they are accessible to the view:

class EmployeeCurrentChange
{    
   public string EmployeeName { get; set; }
   public string EmployeeStreet { get; set; }
   public string EmployeeCity { get; set; }
   public string Etc { get; set; }

   public DateTime ChangeEffective { get; set; }

//I don't need the below properties in the result, but if they 
//happen to be there I don't mind.
   public int EmployeeKey { get; set; }
   [ForeignKey("EmployeeKey")]       
   public virtual Employee Employee { get; set; }

   [Key]
   public int EmployeeKey {get;set;}

   public int CurrentEmployeeChangeKey { get; set; }
   [ForeignKey("CurrentEmployeeChangeKey")]    
   public virtual EmployeeChange CurrentEmployeeChange { 
     get { return EmployeeChanges.FirstOrDefault() ; } /*set;*/ }

   public virtual ICollection<EmployeeChange> EmployeeChanges { get; set; }    

   [Key]
   public int EmployeeChangeKey { get; set; }

}

I've tagged this with reflection because I understand that it may not be possible without using reflection.

score 0 · Answer 1 · edited May 23 '17 at 12:11

Take a look at this question: How to create LINQ Expression Tree to select an anonymous type

Basically he creates a class that can project an anonymous type at runtime, you can probably adapt it for your use. But since its an anonymous type and its generated at runtime you will not get any sort of design time support for it. Since the type is generated at runtime though you can attach attributes to the projection to copy what exists on the current class.

Honestly not sure why you would want to do this as its quite a bit of work, but figured I'd pass along what I knew on the subject.

Flatten/expand columns of Navigation Property for ViewModel?

1 Answers1