private static MethodCallExpression AggCallExpression(AggregationMethod aggMethod, ParameterExpression sourceParameter, LambdaExpression lambda)
{
String methodName;
switch (aggMethod)
{
case AggregationMethod.Average:
methodName = nameof(Enumerable.Average);
break;
case AggregationMethod.CountDistinct:
return(CountDistinctExpression(sourceParameter, lambda));
case AggregationMethod.Max:
methodName = nameof(Enumerable.Max);
break;
case AggregationMethod.Min:
methodName = nameof(Enumerable.Min);
break;
case AggregationMethod.Sum:
methodName = nameof(Enumerable.Sum);
break;
default:
throw new NotSupportedException();
}
MethodInfo closeMethod;
MethodInfo openMethod = OeMethodInfoHelper.GetAggMethodInfo(methodName, lambda.ReturnType);
if (openMethod == null)
{
Func <IEnumerable <Object>, Func <Object, Object>, Object> aggFunc;
switch (aggMethod)
{
case AggregationMethod.Max:
aggFunc = Enumerable.Max <Object, Object>;
break;
case AggregationMethod.Min:
aggFunc = Enumerable.Min <Object, Object>;
break;
default:
throw new InvalidOperationException($"Enumerable.{methodName} not found");;
}
openMethod = aggFunc.GetMethodInfo().GetGenericMethodDefinition();
closeMethod = openMethod.MakeGenericMethod(lambda.Parameters[0].Type, lambda.ReturnType);
}
else
{
closeMethod = openMethod.MakeGenericMethod(lambda.Parameters[0].Type);
}
return(Expression.Call(closeMethod, sourceParameter, lambda));
}
