MySqlDataReader.GetBytes

Question

I have been have a bit of an issue with MySqlDataReader.GetBytes, and referencing the column ordinal.

Table structure:

ID - Primary, int, not null, auto_increment
TNode - , not null
Packet - longblob
Timestamp - timestamp

If I run the following query:

SELECT * FROM table WHERE TNode = 2;

And attempt to get the size of the longblob using the following method:

while (reader.Read()) 
{
     long l = reader.GetBytes(2,0,null,0,0);
}

I will receive the following error:

GetBytes can only be called on binary or guid columns

Which, column index 2 is. Even if I iterate through all of the columns, as expected, I receive the same error. But if I run the following query:

SELECT Packet, ID, Timestamp FROM table WHERE TNode = 2;

Followed by:

while (reader.Read()) 
{
     long l = reader.GetBytes(0, 0, null, 0, 0);
}

No problems. I am able to get the length of the longblob, and do what I need to do with it.

Any ideas as to why it is not allowing me to use a non-zero column index?

Thank you.

try looking at the accepted answer here and do something like what's being done there.. http://stackoverflow.com/questions/11135245/what-length-parameter-should-i-pass-to-sqldatareader-getbytes — MethodMan, May 31 '13 at 18:50
sometimes the easiest things are easily overlooked.. glad I could help — MethodMan, May 31 '13 at 21:19
interesting, what if there are several BLOB columns returned by query? How then this would work long l = reader.GetBytes(0, 0, null, 0, 0);? — Oleksandr, Jan 16 '21 at 11:27

score 0 · Answer 1 · answered May 31 '13 at 18:46

0

Not sure about MySQL, but in SQL Server SELECT * might not return the columns in the order you expect. It might NOT be column 2. In fact, if you change the table and continue to use SELECT * you might introduce a hard-to-find bug. I'd suggest specifying the columns as you did in your test.

answered May 31 '13 at 18:46

n8wrl

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Yeah, I get that. Its weird though, even if the wild card select doesn't return the columns in the expected order, prior to running a GetBytes, if I iterate through the columns and get the index of the Packet column, it still fails if the index greater than 0. – Hammerzeit May 31 '13 at 18:49

MySqlDataReader.GetBytes

1 Answers1