How do I represent an option calculated column with EF Code First?

Question

I have a situation where I have a table of entries that I'll be querying on, but in some cases I'll have additional information available.

For instance, if I have a table of people, I want to be able to search by name, but I also want to store some coordinates and search based on their location, but also expose that distance in the object model. So, for instance, suppose my people table looks something like this:

PersonId int
Name nvarchar(100)
Address nvarchar(100)
Latitude float(10,6)
Longitude float(10,6)

And the entity class is defined like this:

public class Person
{
     public int PersonId { get; set; }
     public sting Name { get; set; }
     public float Latitude { get; set; }
     public float Longitude { get; set; }
}

Then I can easily find a person by name using:

var people = from p in myDb.People where p.Name.Contains("joe");

Now, I have user-defined function called CalculateDistance that I've created to handle this distance calculations. And so my SQL will look something like this:

String sql = "SELECT *, dbo.CalculateDistance(" + location.X + ", " + location.Y + ", Latitude, Longitude) AS Distance FROM people ORDER BY Distance

How do I represent this in code? I've tried adding a property like this to the class:

public virtual float Distance { get; set; }

But then the name queries fail because there is no Distance column. I also tried extending the Person class:

public class PersonWithDistance: Person {
    public float Distance { get; set; }
}

But that caused even more problems with the way the mappings are generated.

What's the correct way to implement something like this? Do I have to create an entirely separate separate class for the results from the distance query?

Answer 1

This is not very nice design. You should have distance as a method of either Person or some helper class and compute distance in your application not in database. It whould also require transfering location to the person.

Anyway if you want to add some property which is not mapped to column in database you must exclude it from mapping. This can be done either by attribute:

[NotMapped]
public float Distance { get; set; }

or by fluent API:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);

    modelBuilder.Entity<Person>().Ignore(p => p.Distance);
}

Answer 2

Well I ended up creating a PersonResult class which contains an Id, Distance and a Person object, like this:

public class PersonResult {
     [Key]
     public int PersonId { get; set; }
     public double Distance { get; set; }
     public virtual Person Person { get; set; }
}

I populate that from a stored procedure like this:

var results = myDb.PersonResults.SqlQuery("EXEC PeopleByDistance " + lat + ", " + lng);

And loop through the results to populate the Person objects:

foreach (PersonResultresult in results)
{
    result.Person = myDb.People.Where(p => p.PersonId == result.PersonId).FirstOrDefault();
}

That seems to work well. Although I'm not sure that's the best way to handle it.