Entity framework relationships

Question

I have these three entities:

public class Dog
{
    public int DogId { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
    publ         


        

Answer 1

It is not really a good idea to do many to many relationships like how you've done. See here

In order to get a proper many to many relationship, mapped in the proper way in the database, that doesn't have pitfalls, I would try it this way:

public class Dog {}
public class Event {}

public class Result {}

// This is a linking table between Dog and Results
public class DogResult
{
    public int Id {get;set;}
    public int DogId {get;set;}
    public int ResultId {get;set;}
}

// This is a linking table between Events and Results
public class EventResult
{
    public int Id {get;set;}
    public int EventId {get;set;}
    public int ResultId {get;set;}
}

When you now write your query you can do this:

using (var context = new DbContext())
{
   var dogs = context.Dogs();
   var dogResults = context.DogResults();
   var results = context.Results();

   var dogsAndResults = dogs.Join(
          dogResults,
          d => d.Id,
          r => r.DogId,
          (dog, dogResult) => new { dog, dogResult })
       .Join(
          results,
          a => a.dogResult.ResultId,
          r => r.Id,
          (anon, result) => new { anon.dog, result });
}

It is a bit nasty looking, but it will give you back a list of anonymous objects containing a Dog and its related Result. But obviously it would be better to do this in a stored proc:

using (var context = new DbContext())
{
    var results = context.Database.ExecuteStoreQuery("SELECT * .... JOIN ... ");
}

This is cleaner, because you are using SQL.

This is a more complex way of dealing with it. But far more performant, especially if you understand fully how entity framework executes LINQ.

Obviously if you want to create these links:

using (var context = new DbContext()) 
{
    context.Dogs.AddRange(dogs); // dogs being a list of dog entities
    context.Results.AddRange(results); // events being a list of results entities

    context.DogResults.AddRange(dogResults); // a list of the links
}

It is completely up to you how you create these links. To turn this into a sproc as well, you want to create some custom User Defined Table Types and use them as a Table Value Parameter.

var dogResults = dogs.SelectMany( d => results.Select ( r => new DogResult { DogId = d.Id, ResultId = r.Id } ) );

That is a beast of a LINQ query and basically it gets every dog and links it to every result. Run it in LinqPad and Dump the values.