How to map a table to an enumerable property using entity framework? (Database first)

Question

Suppose I had these two classes:

public class MyClass {
    public int Id { get; set; }
    public IEnumerable<MyData> MyDataCollection { get; set; }
}

public class MyData {
    public int DataId { get; set; }
    public string Data { get; set; }
    public int Id { get; set; }
}

and I had two tables in my database:

MyClasses:
Id
1
2


MyDatas:
DataId     Id       Data
1       -  1    -  "Hello"
2       -  1    -  "World"
3       -  2    -  "Hello World"

How do I use entity framework to link them up, so that I can do:

using (var db = new DataContext()) {
     var data = db.MyClass.Where(c => c.ID == 1).MyDataCollection;
     foreach (var item in data) Console.WriteLine(item.Data);
}

I have the other data but so far I've just written [NotMapped] above the MyDataCollection property, but obviously I want to get rid of that and have it mapped. How do I (correctly) map it?

Answer 1

You can do it by expanding your class with appropriate navigation properties to establish the joins between them by following EF standards

public class MyClass {
    public MyClass()
    {
       MyDataCollection = new List<MyData>();
    }
    public int Id { get; set; }
    public virtual ICollection<MyData> MyDataCollection { get; set; }
}

public class MyData {
    public int DataId { get; set; }
    public string Data { get; set; }
    public int Id { get; set; }
    public virtual MyClass MyClass { get; set; }
}

Make sure these 2 entities are declared in the dbcontext as below

public class MyContext: DbContext 
{
    public MyContext(): base()
    {

    }

    public DbSet<MyClass> MyClasses { get; set; }
    public DbSet<MyData> MyDatas { get; set; }            
}