/// <summary>Creates and executes a DataServiceQuery based on the passed in expression which results a single value</summary>
/// <typeparam name="TElement">generic type</typeparam>
/// <param name="expression">The expression for the new query</param>
/// <returns>single valued results</returns>
internal TElement ReturnSingleton <TElement>(Expression expression)
{
IQueryable <TElement> query = new DataServiceQuery <TElement> .DataServiceOrderedQuery(expression, this);
MethodCallExpression mce = expression as MethodCallExpression;
Debug.Assert(mce != null, "mce != null");
SequenceMethod sequenceMethod;
if (ReflectionUtil.TryIdentifySequenceMethod(mce.Method, out sequenceMethod))
{
switch (sequenceMethod)
{
case SequenceMethod.Single:
return(query.AsEnumerable().Single());
case SequenceMethod.SingleOrDefault:
return(query.AsEnumerable().SingleOrDefault());
case SequenceMethod.First:
return(query.AsEnumerable().First());
case SequenceMethod.FirstOrDefault:
return(query.AsEnumerable().FirstOrDefault());
case SequenceMethod.LongCount:
case SequenceMethod.Count:
return(((DataServiceQuery <TElement>)query).GetValue(this.Context, ParseQuerySetCount <TElement>));
case SequenceMethod.SumIntSelector:
case SequenceMethod.SumDoubleSelector:
case SequenceMethod.SumDecimalSelector:
case SequenceMethod.SumLongSelector:
case SequenceMethod.SumSingleSelector:
case SequenceMethod.SumNullableIntSelector:
case SequenceMethod.SumNullableDoubleSelector:
case SequenceMethod.SumNullableDecimalSelector:
case SequenceMethod.SumNullableLongSelector:
case SequenceMethod.SumNullableSingleSelector:
case SequenceMethod.AverageIntSelector:
case SequenceMethod.AverageDoubleSelector:
case SequenceMethod.AverageDecimalSelector:
case SequenceMethod.AverageLongSelector:
case SequenceMethod.AverageSingleSelector:
case SequenceMethod.AverageNullableIntSelector:
case SequenceMethod.AverageNullableDoubleSelector:
case SequenceMethod.AverageNullableDecimalSelector:
case SequenceMethod.AverageNullableLongSelector:
case SequenceMethod.AverageNullableSingleSelector:
case SequenceMethod.MinSelector: // Mapped to a generic expression - Min(IQueryable`1<T0>, Expression`1<Func`2<T0, T1>>)->T1
case SequenceMethod.MaxSelector: // Mapped to a generic expression - Max(IQueryable`1<T0>, Expression`1<Func`2<T0, T1>>)->T1
case SequenceMethod.CountDistinctSelector: // Mapped to a generic expression - CountDistinct(IQueryable`1<T0>, Expression`1<Func`2<T0, T1>>)->Int32
return(((DataServiceQuery <TElement>)query).GetValue(this.Context, this.ParseAggregateSingletonResult <TElement>));
default:
throw Error.MethodNotSupported(mce);
}
}
// Should never get here - should be caught by expression compiler.
Debug.Assert(false, "Not supported singleton operator not caught by Resource Binder");
throw Error.MethodNotSupported(mce);
}