/// <summary>
/// Translates the specified linq expression into a <c ref="LinqQueryDescription" />.
/// </summary>
/// <param name="expression">The linq expression.</param>
/// <returns></returns>
internal LinqQueryDescription Translate(Expression expression)
{
_query = new LinqQueryDescription();
if (expression.Type.IsGenericType)
{
_query.ElementType = expression.Type.GetGenericArguments()[0];
}
Visit(expression);
return(_query);
}
public override object Execute(Expression expression)
{
LinqQueryDescription queryDescription = Translate(expression);
// Call the API..
string xml = _proxy.FindElements(queryDescription);
Response response = ModelSerializer.DeserializeTo <Response>(xml);
// Guard against an empty response..
IModelList elementCollection = (response == null)
? (IModelList)Activator.CreateInstance(queryDescription.ElementListType) // TODO: too much going on here, needs tidying up
: response.GetTypedProperty(queryDescription.ElementListType);
if (queryDescription.ClientSideExpression == null)
{
return(elementCollection);
}
switch (queryDescription.ClientSideExpression)
{
case "FirstOrDefault":
return(elementCollection.Count == 0
? null
: elementCollection[0]);
case "First":
if (elementCollection.Count == 0)
{
throw new InvalidOperationException("The ModelList contains no items");
}
return(elementCollection[0]);
case "SingleOrDefault":
if (elementCollection.Count > 1)
{
throw new InvalidOperationException("The ModelList contains no items");
}
if (elementCollection.Count == 0)
{
return(null);
}
return(elementCollection[0]);
case "Single":
if (elementCollection.Count != 1)
{
throw new InvalidOperationException("The ModelList contains no items");
}
return(elementCollection[0]);
case "Count":
return(elementCollection.Count);
default:
throw new NotImplementedException(string.Format("The client side aggregator {0} cannot currently be performed", queryDescription.ClientSideExpression));
}
}