private LambdaExpression GetOrderSelectorExpression(SortInstruction sortInstruction)
{
if (!_fieldProvider.FieldExists(sortInstruction.FieldName))
{
throw new FieldNotFoundException(sortInstruction.FieldName, false);
}
IFieldCollator <TItem> fieldCollator = _fieldProvider.GetCollator(sortInstruction.FieldName);
if (fieldCollator == null)
{
throw new FieldOperationNotAllowedException(sortInstruction.FieldName, FieldOperation.Sort);
}
try
{
ParameterExpression itemPram = Expression.Parameter(typeof(TItem), "srt");
LambdaExpression getterLambda = fieldCollator.GetSortExpression(itemPram);
if (getterLambda == null)
{
throw new NullReferenceException("No sort expression was defined for this field.");
}
return(getterLambda);
}
catch (Exception ex)
{
throw new FieldCannotFilterException(sortInstruction.FieldName, ex);
}
}
/// <remarks>
/// Ideas from https://stackoverflow.com/questions/5094489
/// </remarks>
private Expression <Func <TItem, bool> > GetFilterPredicateExpression(FilterInstruction filterInstruction)
{
if (!_fieldProvider.FieldExists(filterInstruction.FieldName))
{
throw new FieldNotFoundException(filterInstruction.FieldName, false);
}
IFieldCollator <TItem> fieldCollator = _fieldProvider.GetCollator(filterInstruction.FieldName);
if (fieldCollator == null)
{
throw new FieldOperationNotAllowedException(filterInstruction.FieldName, FieldOperation.Filter);
}
try
{
ParameterExpression itemPram = Expression.Parameter(typeof(TItem), "fltr");
Expression filterExpression = fieldCollator.GetFilterExpression(itemPram, filterInstruction.Operator, filterInstruction.ValueString);
if (filterExpression == null)
{
throw new ArgumentNullException(nameof(filterExpression), "No filter expression was defined for this field.");
}
Expression <Func <TItem, bool> > predicateLambda = Expression.Lambda <Func <TItem, bool> >(filterExpression, itemPram);
return(predicateLambda);
}
catch (Exception ex)
{
throw new FieldCannotFilterException(filterInstruction.FieldName, ex);
}
}