Typed “Find” method in Dynamic data store

On the morning train to work, I played around with the DDS, and made a couple of extension methods to fix something I’ve been irritated about for a while.

The “typed” find method in the DDS takes the name of a property, and the value the property must have to receive the object from the store. This isn’t that nice, and I’m the one to blame. Therefore, I’ve created the following two extensions:

public static IEnumerable<TStore> Find<TStore, TFind>(this DynamicDataStore store, Expression<Func<TStore, TFind>> property, TFind value)
   {
        string propertyName = MultipleFind<TStore>.GetPropertyName<TFind>(property);
        return store.Find<TStore>(propertyName, value);
   }

public static IEnumerable<TStore> Find<TStore>(this DynamicDataStore store, MultipleFind<TStore> find)
{
    return store.Find<TStore>(find.Dictionary);
}

Those extension methods uses the following class that I needed to create:

    public class MultipleFind<TStore>
    {
        private Dictionary<string, object> _find;
        public MultipleFind()
        {
            _find = new Dictionary<string, object>();
        }
        public void Add<TFind>(Expression<Func<TStore, TFind>> property, TFind value)
        {
            _find.Add(GetPropertyName<TFind>(property), value);
        }
        public static string GetPropertyName<TFind>(Expression<Func<TStore, TFind>> property)
        {
            MemberExpression member = property.Body as MemberExpression;
            if (member == null)
            {
                throw new NotSupportedException("Find method only works directly against properties at the moment");
            }
            return member.Member.Name;
        }
        public Dictionary<string, object> Dictionary
        {
            get
            {
                return new Dictionary<string, object>(_find);
            }
        }
    }

Those can be used like this:

var result = _personStore.Find<Person, int>(p => p.ShoeSize, 40);

MultipleFind<Person> findings = new MultipleFind<Person>();
findings.Add(p => p.ShoeSize, 40);
findings.Add(p => p.FirstName, "Jonas");
var result2 = _personStore.Find<Person>(findings);

Compared with:

var result = personStore.Find<Person>("ShoeSize", 40);
Dictionary<string, object> search = new Dictionary<string, object>();
search.Add("ShoeSize", 40);
search.Add("FirstName", "Jonas");
var result2 = personStore.Find<Person>(search);