Question

I’m in charge to migrate our own DAL to a solution based on Entity Framework 4 but, before I can do it, I need to be sure it’s possible to translate all our “constructs” to this new technology.

One of the biggest issues I’m having is the possibility to read a field and build a custom type. Valid examples could be a bit mask saved in a BIGINT field, a list of mail addresses saved as a CSV list in a NVARCHAR field or an XML field containing aggregated data not worth to have their own table/entity. Basically the serialization mechanism is not fixed.

Let’s take the classic “Address” example.

public class Address
{
    public string Street {get; set;}
    public string City {get; set;}
    public string Zip {get; set;}
    public string Country {get; set;}
}

and let’s suppose we want to save it in an XML field using this template:

<address>
  <street>Abrahamsbergsvägen, 73</street>
  <city>Stockholm</city>
  <zip>16830</zip>
  <country>Sweden</country>
</address>

The question basically is: does exist a method to override how EF4 serializes and deserializes the content of a field mapped to a property of an entity?

Answer 1

I found this solution. It’s not as clean as I wished but it seems it’s impossible to get anything better.

given this base entity,

public class Institute
{
    public int InstituteID { get; set; }
    public string Name { get; set; }
    // other properties omitted
}

I added in the database an XML field called Data containing some strings using this simple template

<values>
  <value>Value 1</value>
  <value>Value 2</value>
  <value>Value 3</value>
</values>

In the entity I added these properties and I mapped the database field “Data” to the property “DataRaw”.

protected string DataRaw
{
    get
    {
        if (_Data == null)
            return _DataRaw;
        else
            return new XElement("values", from s in Data select new XElement("value", s)).ToString();
    }
    set
    {
        _DataRaw = value;
    }
}

private string _DataRaw;
private string[] _Data;

public string[] Data
{
    get
    {
        if (_Data == null)
        {
            _Data = (from elem in XDocument.Parse(_DataRaw).Root.Elements("value")
                     select elem.Value).ToArray();
        }
        return _Data;
    }

    set
    {
        _Data = value;
    }
}

This solution works. Here is the sample code:

class Program
{
    static void Main(string[] args)
    {
        var ctx = new ObjectContext("name=TestEntities");

        var institute = ctx.CreateObjectSet<Institute>().First();

        System.Console.WriteLine("{0}, {1}", institute.InstituteID, institute.Name);
        foreach (string data in institute.Data)
            System.Console.WriteLine("\t{0}", data);

        institute.Data = new string[] { 
            "New value 1",
            "New value 2",
            "New value 3"
        };

        ctx.SaveChanges();
    }
}

Does anyone have a better solution?