Question

I’m working on a wiki project. MVC3 + EF4 Code First.

All classes from my model inherit from a main “EditBase” class. This assures that they all have ID, Username and CreatedDate. It also helps me create a generic Repository for basic CRUDs.

I wish to define a new entity called AbuseReport to handle flagging of incorrect/innacurate content:

public class AbuseReport : EditBase
{
    public DateTime DateReported { get; set; }
    public string EntityType { get; set; }
    public int EntityId { get; set; }
    public int ReportTypeId { get; set; }
    public ReportType ReportType 
    {
        get { return (ReportType) this.ReportTypeId; }
        set { this.ReportTypeId = (int) value; }
    }
    public string Description { get; set; }
}

What would be the easiest way to retrieve an entity stored on the database starting from the information on a AbuseReport object? I can’t use foreign keys because the report can refer to any entity on the project.

I would need to call something like this:

Type modelType;
entityDictionary.TryGetValue(entityName, out modelType);
var rep = new Repository<modelType>();

Answer 1

I would store all the model types in the same repository. The repository key will have to contain the type of the model as well as its ID. I use the local class RepositoryKey for this purpouse:

public class EditBase
{
    public int ID { get; set; }
    public string Username { get; set; }
    public DateTime CreatedDate { get; set; }
}

public class Repository
{
    private Dictionary<RepositoryKey, EditBase> _store = new Dictionary<RepositoryKey, EditBase>();

    public void Add(EditBase model)
    {
        _store.Add(new RepositoryKey(model), model);
    }

    public void Remove(EditBase model)
    {
        _store.Remove(new RepositoryKey(model));
    }

    public void Remove<T>(int id)
        where T : EditBase
    {
        _store.Remove(new RepositoryKey(typeof(T), id));
    }

    public bool TryGet<T>(int id, out T value)
        where T : EditBase
    {
        EditBase editBase;
        if (!_store.TryGetValue(new RepositoryKey(typeof(T), id), out editBase)) {
            value = null;
            return false;
        }
        value = (T)editBase;
        return true;
    }

    private class RepositoryKey : IEquatable<RepositoryKey>
    {
        private Type _modelType;
        private int _id;

        public RepositoryKey(EditBase model)
        {
            _modelType = model.GetType();
            _id = model.ID;
        }

        public RepositoryKey(Type modelType, int id)
        {
            _modelType = modelType;
            _id = id;
        }

        #region IEquatable<IdentityKey> Members

        public bool Equals(RepositoryKey other)
        {
            if (_modelType != other._modelType) {
                return false;
            }
            return _id == other._id;
        }

        #endregion

        public override int GetHashCode()
        {
            return _modelType.GetHashCode() ^ _id.GetHashCode();
        }
    }
}