I have a problem accessing large blob data when several query are
performed sequentially
I have on a Real SQL Server a database, with a table 'contracts'
every contract can have a list of pdf files. They are stored in a
blob column on another db on the same server.
on the contract form I show the list of pdf files on a listbox, and
there is a button 'show' that essentially store the blob data of the
selected item on a temporary file and then launches the file to show
it with the default reader:
Dim f As FolderItem
Dim b As BinaryStream
dim rs as RecordSet
rs = dbfile.SQLSelect("Select do_documento from documenti where
do_id= ..... // selects the blob column form table
if dbfile.Error then
MsgBox "Error getting image: " + dbfile.ErrorMessage
return
end if
if rs = nil then
msgbox "nil"
return
end if
f = TemporaryFolder.Child( filename)
b = f.CreateBinaryFile("special/any")
if b = nil then
msgbox "error creating file"
return
end if
b.Write rs.Field("do_documento").NativeValue
rs = nil
b.Close
f.launch
It works well, if I wait a good delay ( 10 seconds or so ) between
each export operation, but if i select another file from the list and
click 'show' just after a previous file is shown in the pdf viewer
( just like a user would probably do ),
the recordset returns nil;
the Real SQL Server log shows this error message:
checkErrorConditions: wrong protocol signature
if I click again the 'show' button the records return 'nil' again,
and finally clicking again I have this error from dbfile.errormessage:
Error getting image: There was an error communicating with the server
[sending HEADER]. The server may be down or not responding. and so
on. It seems I'm disconnected at this time.
What's happening? is the retrieving of a big blob field synchronous
or not? ( it should be, since I read it, store ot on a file and
immediately show it with the launch command.
what else is happening in asynchronous mode that may affect the
subsequent query of blob data? and how can I check where all is
finished to perform the next query?
thank you,
Giulio
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