is it a correct database design?

Question

I'm working with EF 5, Web Api and MVC4 i need help about this database design. I need save in database the city and town of a hospital, but without cycles, a hospital has one city and town, and a city has many towns

public class City
{
    public int CityId { get; set; }
    public List<Town> Towns { get;  set; }
    public string Name { get; set; }
    [Timestamp]
    public byte[] RowVersion { get; set; }

    public City()
    {
        Towns = new List<Town>();
    }
}

 public class Town
{
    public int TownId { get; set; }

    public int CityId { get; set; }

    public string Name { get; set; }

    public byte[] RowVersion { get; set; }
}

 public class Hospital
{
    public int HospitalId { get; set; }

    [Required]
    public string Name { get; set; }

    public int TownId { get; set; }
    public  Town Town { get; set; }

    public int CityId { get; set; }

    public City City { get; set; }

    public bool IsAvailable { get; set; }

    [Timestamp]
    public byte[] RowVersion { get; set; }


    public Hospital()
    {
      this.IsAvailable = true;
    }
}

I don't like the property City in Hospital class, but i need another option, it's like a cycle

Answer 1

What's wrong with the "cycle"? EF uses them all the time, and bi-directional navigation is quite useful! Of course, it breaks when trying to serialize, but you shouldn't be doing that anyways :).

As to your question, if a City "has" multiple Towns, and a Hospital is in a town, then there is no need for a Hospital to know about a City. It knows what town it is in, and thus what City it is in. Of course, if a given Town can be in more than one City, (but the Hospital is in one unique pair) then your design looks perfect.

With the information you gave, I would just remove the "City" property from the Hospital class altogether. If you need to access it, just go through the Town property.

myHospital.Town.City

Answer 2

Well, if each Town is related to a single City, and each Hospital is related to a single Town, then you can use these relations to find the Hospital's City easily.

You don't need to have the City as a column in the Hospital table in the database, however you might want to still have it as a property in the code for simplicity.
in that case, the easy way to do it is to connect the Hospital class to a view rather then the actual Hospital table.

Answer 3

If I would write that application, I would take classes like this.

City does not contain any relation property:

public class City
{
    public int Id { get; set; }
    public string Name { get; set; }
    [Timestamp]
    public byte[] RowVersion { get; set; }
}

Town is in any City

public class Town
{
    public int Id { get; set; }
    public int CityId { get; set; }
    public string Name { get; set; }
    public byte[] RowVersion { get; set; }
}

And Hospital is in Town. You can access City by TownId

public class Hospital
{
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
    public int TownId { get; set; }

    //you can uncomment this for less coding for searching, filtering etc..
    //public int CityId { get; set; }

    public bool IsAvailable { get; set; }
    [Timestamp]
    public byte[] RowVersion { get; set; }
    public Hospital()
    {
      this.IsAvailable = true;
    }
}