 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
VB Forum / Database Access / June 2007AppendChunk method resulting in wrong data
Hi, Having a bit of trouble with the Parameter.AppendChunk method. The test output from the below code is as follows: Trace: param first byte: 0 Trace: param second byte: 255 Trace: Source first byte: 255 Trace: Original file length: 711 Trace: total bytes appended to param: 711 Trace: final param length: 712 Trace: param last byte: 217 Trace: Source last byte: 217 For some reason it appears that the first time I'm call the method, it's putting a 0 in the first byte of the Parameter value. It's my understanding that the first time the method is called it's supposed to replace the current contents of the value, and when I've done these tests against field objects using that that object's version of the same method it works fine. In this case however, after I've stored the data to the parameter's value field it is always 1 byte longer than the original data and when I call Command.Execute, that same data with the extra 0 byte is stored to the data source. Unless I've done something specifically wrong here, it appears that this might be an ADO bug because I've tried it against two different data source providers and have the same results. Thanks Eric ' get a reference an empty byte array ' to read byte arrays from test file binArr = TestFunctions.GetByteArr() Set param1 = command1.CreateParameter( _ "@binValue", adLongVarBinary, _ adParamInput,_ fileSize+1, binArr) Set param2 = command1.CreateParameter( _ "@Key", adInteger, _ adParamInput, 0, 0) command1.Parameters.Append param1 command1.Parameters.Append param2 command1.Parameters("@Key") = 1 For each col_name in testArr strSQL = "UPDATE ado_test SET " & _ col_name & " = ? WHERE " & key_column & " = ?" command1.CommandText = strSQL blockSize = 100 While bytesTotalWritten <> fileSize If fileSize - bytesTotalWritten < blockSize Then blockSize = fileSize - bytesTotalWritten End If ' Reads binary file on block at a time iReturn = TestFunctions.GetBytesFromFile( _ binArr, bytesTotalWritten, _ blockSize, FILE ) ' write the bytes to the field command1.Parameters("@binValue").AppendChunk (binArr) 'DEBUG If bFirst Then Assert.Trace "param first char: " & Int(ascB(MidB (command1.Parameters("@binValue"), 1,1))) Assert.Trace "param second char: " & Int(ascB(MidB (command1.Parameters("@binValue"), 2,1))) Assert.Trace "Source first char: " & Int(ascB(MidB (binArr,1,1))) End If bytesTotalWritten = bytesTotalWritten + blockSize bFirst = cBool(false) Wend ' DEBUG Assert.Trace "Original file length: " & fileSize Assert.Trace "total bytes appended to param: " & bytesTotalWritten Assert.Trace "final param length: " & lenB(command1.Parameters("@binValue")) Assert.Trace "param last char: " & Int(ascB(MidB (command1.Parameters("@binValue"), 712,1))) Assert.Trace "Source last char: " & Int(ascB(MidB (binArr,11,1))) command1.execute Next I should add that when creating the first parameter to store the binary data, I was forced to declare the size so.. Set param1 = command1.CreateParameter( _ "@binValue", adLongVarBinary,_ adParamInput, fileSize+1, binArr) If I stated the size of the field as fileSize which is the exact size of the date, I get this error when I perform command.Execute Probably this is because the extra 0 as the first byte is causing an overflow if I don't create the param with an extra byte in it Error: Source: ADODB.Command Line 202 Column 2 Application uses a value of the wrong type for the current operation. I've determined where the extra byte is coming from but I'm not sure what to do about it. I'm doing this in VBs, and since byte() are not supported there I'm calling a DLL I made in VB6 to create and modify them for me. When I do this... >' get a reference an empty byte array >' to read byte arrays from test file >binArr = TestFunctions.GetByteArr() I'm calling... Public Function GetByteArr() As Byte() Dim arr(0) As Byte GetByteArr = arr End Function If I change the dimension to arr(10), then the length of my final parameter value goes up by 10. What I'm unlear about is that supposedly the first time you call appendChunk, it's supposed to initialize the variable. I've tried to dimension it as arr() as Byte, but then when I do this it tells me I'm trying to use the wrong data type. >Set param1 = command1.CreateParameter( _ > "@binValue", adLongVarBinary, _ > adParamInput,_ > fileSize+1, binArr) Is there a more appropriate way to initialize the array that I haven't tried? Thanks Eric > I've determined where the extra byte is coming from but I'm not sure > what to do about it. I'm doing this in VBs, and since byte() are not [quoted text clipped - 26 lines] > Is there a more appropriate way to initialize the array that I haven't > tried? Have you tried omitting the value arg when you create the parameter object? Perhaps CreateParameter internally calls AppendChunk if/when a value is explicitly passed? Also, there is another way to transfer blob values that works with recordset fields, so should work with Parameter values as well: Dim s As ADODB.Stream Set s = New ADODB.Stream s.Mode = adModeReadWrite s.Type = adTypeBinary s.Open ' load binary contents of into stream ' assumes FileName is the name of an existing file s.LoadFromFile FileName ' set position to beginning of stream s.Position = 0 ' insert a row (or otherwise position record pointer) rs.AddNew ' assign other fields as required ' ... ' assumes image field name is 'blob' rs.Fields("blob").value = s.Read() rs.Update s.Close -Mark > Thanks > Eric Mark, Yes, good call, that's exactly what it was doing. Thanks Just out of curiousity, is there a direct way to read data a block at a time from a Stream? Here I've been using the Get method as follows Open FilePath For Binary Access Read As #fileIndex Get #fileIndex, offset, arrBin2 Close Thanks Eric >Have you tried omitting the value arg when you create the parameter object? >Perhaps CreateParameter internally calls AppendChunk if/when a value is [quoted text clipped - 29 lines] >> Thanks >> Eric > Mark, > [quoted text clipped - 6 lines] > Get #fileIndex, offset, arrBin2 > Close The Stream's Read method accepts an optional NumBytes parameter, but I'm not sure how it could be used to chunk-up a blob parameter -- I take it you're working with large files and need to show progress? If that's the case, the stream may not offer you any advantages. As I was drafting this, and experimenting a little in an unsaved project, I noticed that Open accepts adOpenStreamAsync as an option, but apparently that only applies to certain types of sources. I also saw that loading a multi-hundred MB file into a stream blocks for longer than most users like to see a frozen UI... But my experiment ended when I was left once again to lament that VB6's debugger somehow parents the debug target, such that msgbox blocks access to the debugger IDE -- gah what a horrible design flaw! You'd think they'd have provided some way to kill the debug target without killing the IDE, no matter what the target was doing, ala VS[every version I've used] C++ apps, but oh no... Anyway, good luck with your project. -Mark > Thanks > Eric [quoted text clipped - 34 lines] >>> Thanks >>> Eric |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.