How to get number of rows from NpgsqlDataReader

Question

I am trying to get the number of rows from the NpgsqlDataReader after using a select statement. The reason I am trying to check is to see if it has any data, a single row, or if it has multiple rows before working with the data. Any help will be greatly appreciated.

This is being done in C# .NET 4

Answer 1

From a bit of googling the NpgsqlDataReader would seem to be very similar to the sqldatareader. The sqldatareader does not have a built in way to get the row count. It would appear you would have to loop through and perform your own count if you wanted to get the rowcount.

Answer 2

If the NpgsqlDataReader inherits from DbDataReader as other DataReaders do, you can check with

if (reader.HasRows) {...}

if there are any results. But I don't think that you can get the actual number of rows without looping through the reader....

Answer 3

If you only want a quick preview.

1.) does not have a result 2.) does have one result 3.) does have multiple results

you could execute the similar SQL Statement with a LIMITer. This should be very fast. And after that execution, you are going to retrieve the complete data.

example:

select * from [TABLE] where [CONDITION] LIMIT 2

if you get 0 rows, no result / if you get 1 row, one result / if you get 2 rows, multiple results

Answer 4

I would also like to get the number of rows for progress bar, but it seems I can't iterating twice is too much work for just showing progress ;)

You can create a proxy class, which is a child of NpgsqlDataReader and where you re-implement iterator (extends IEnumerable), which will implicitly iterate over first up to 2 rows if you either .Read() or ask .CountClass - then it will give those 2 from it's cache before directly reading the rest.