Complex Type Ignored by Entity Framework Code First

问题

Building on Ladislav's answer to

Entity Framework Code First and Collections of Primitive Types

I'm attempting to create a wrapper type EfObservableCollection<T> around an ObservableCollection<T> that has an additional helper property to simplify persistence (certainly this solution has trade-offs, but it's seems workable for my domain).

However, properties of type EfObservableCollection<T> seem to be ignored by EF. No appropriate columns are created in the database. Guessing that implementing IEnumerable<T> might trigger EF to ignore that type, I commented out that implementation with no change in behavior.

What am I missing here?

Entity Class

public class A
{
    [DataMember]
    public long Id { get; set; }

    [DataMember]
    public string Text { get; set; }

    // Tags is not persisted
    [DataMember]
    public EfObservableCollection<string> Tags { get; set; }
}

Wrapper Class

[ComplexType]
public class EfObservableCollection<T> : IEnumerable<T>
{
    const string VALUE_SEPARATOR = "\x8"; // Backspace character.  Unlikely to be actually entered by a user.  Assumes ASCII or UTF-8.
    readonly string[] VALUE_SEPARATORS = new string[] { VALUE_SEPARATOR };

    [NotMapped]
    protected ObservableCollection<T> Collection { get; private set; }

    public EfObservableCollection()
    {
        Collection = new ObservableCollection<T>();
    }

    [DataMember]
    public string PersistHelper
    {
        get
        {
            string serializedValue = string.Join(VALUE_SEPARATOR, Collection.ToArray());

            return serializedValue;
        }
        set
        {
            Collection.Clear();
            string[] serializedValues = value.Split(VALUE_SEPARATORS, StringSplitOptions.None);
            foreach (string serializedValue in serializedValues)
            {
                Collection.Add((T)Convert.ChangeType(serializedValue, typeof(T))); // T must implement IConvertable, else a runtime exception.
            }
        }
    }

    public void Add(T item)
    {
        Collection.Add(item);
    }

    IEnumerator<T> GetEnumerator()
    {
        return Collection.GetEnumerator();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

回答1:

It turns out that Entity Framework does not like the generic class EfObservableCollection<T>.

If I derive a non-generic class from that class, data is persisted as expected:

[ComplexType]
public class EfObservableCollectionString : EfObservableCollection<string>
{
}

回答2:

Joining backspace with list of strings causes cleaning last character in each string item. I think serialization to json using System.Web.Script.Serialization.JavaScriptSerializer is better.

来源：https://stackoverflow.com/questions/8349682/complex-type-ignored-by-entity-framework-code-first

标签

entity-framework-4

ef-code-first