How can I get around this problem with interfaces?

Question

I am using Entity Framework and that is where my problem is, but probably it is not relevant since I think this is a general C # question.

I have a MyContext class that has many DbSet<T> properties.

To unit test it, I edited MyContext, so they IDbSet<T> instead and mock him. IDbSet<T> is part of the Entity Framework, and DbSet implements it, so they are almost identical.

Everything works fine, because I can do IDbSet<T> all I could do to DbSet<T>

All but one - DbSet has a method called SqlQuery(..) , which I also want to be able to call from my IDbSet .

Since I cannot change DbSet or IDbSet , this leaves me with a riddle. I can’t understand how I can do this, so my IDbSet may have a SearchQuery(..) method added to it in some logical way.

It makes sense? I'm very confused, so maybe I skipped something very simple, like copy and paste IDbSet and rename it and add SearchQuery() . Any ideas?

Answer 1

EDIT

I believe I got what you are looking for - wrappers are everywhere, there may be more problems than it costs, but it's worth a look:

 // An interface which implements IDbSet<T> and adds on the method you want public interface IExtendedDbSet<T> : IDbSet<T> where T : class { DbSqlQuery<T> SqlQuery(string sql, object[] parameters); } // Implement this interface by wrapping around a regular DbSet<T>. // You implement all the methods and properties by just wrapping the DbSet<T> // calls public class ExtendedDbSet<T> : IExtendedDbSet<T> where T : class { private readonly DbSet<T> _dbSet; public ExtendedDbSet(DbSet<T> dbSet) { _dbSet = dbSet; } DbSqlQuery<T> IExtendedDbSet<T>.SqlQuery(string sql, object[] parameters) { return _dbSet.SqlQuery(sql, parameters); } T IDbSet<T>.Add(T entity) { return _dbSet.Add(entity); } T IDbSet<T>.Attach(T entity) { return _dbSet.Attach(entity); } TDerivedEntity IDbSet<T>.Create<TDerivedEntity>() { return _dbSet.Create<TDerivedEntity>(); } T IDbSet<T>.Create() { return _dbSet.Create(); } T IDbSet<T>.Find(params object[] keyValues) { return _dbSet.Find(keyValues); } ObservableCollection<T> IDbSet<T>.Local { get { return _dbSet.Local; } } T IDbSet<T>.Remove(T entity) { return _dbSet.Remove(entity); } IEnumerator<T> IEnumerable<T>.GetEnumerator() { return ((IEnumerable<T>)_dbSet).GetEnumerator(); } IEnumerator IEnumerable.GetEnumerator() { return ((IEnumerable)_dbSet).GetEnumerator(); } Type IQueryable.ElementType { get { return ((IQueryable)_dbSet).ElementType; } } Expression IQueryable.Expression { get { return ((IQueryable)_dbSet).Expression; } } IQueryProvider IQueryable.Provider { get { return ((IQueryable)_dbSet).Provider; } } } // A regular context class, no special interfaces to implement or // custom properties or anything. public class MyContext : DbContext { public DbSet<Car> Cars { get; set; } } // An interface representing your context, which exposes extended DbSet<T> // for your sets. Also define SaveChanges() and whatever else you may need // to call on your context object. public interface IMyContext : IDisposable { IExtendedDbSet<Car> Cars { get; } int SaveChanges(); } // A wrapper around your regular context. For each set, return an // ExtendedDbSet<T> wrapper. public class MyContextWrapper : IMyContext { private readonly MyContext _myContext; public MyContextWrapper(MyContext myContext) { _myContext = myContext; } IExtendedDbSet<Car> IMyContext.Cars { get { return new ExtendedDbSet<Car>(_myContext.Cars); } } void IDisposable.Dispose() { _myContext.Dispose(); } int IMyContext.SaveChanges() { return _myContext.SaveChanges(); } } // Define your context variable as IMyContext, and create it // by creating a wrapper around a regular context. The properties // of the interface will be extended wrappers around your sets. internal class Program { private static void Main(string[] args) { using (IMyContext context = new MyContextWrapper(new MyContext())) { Console.WriteLine(context.Cars.SqlQuery("select 1", new object[0])); } } } 

Answer 2

Hmm, this may not be the most elegant solution, but you can simply write an extension method as follows:

 public IEnumerable<T> SearchQuery(this IDbSet<T> set, string query) { var dbSet = set as DbSet<T>; if (dbSet != null) { return dbSet.SqlQuery(query); } else { throw new NotSupportedException(); } }