Обсуждение: Storing Binary Data
I would like to know how to store and retrieve binary data in PostgreSQL thourgh ODBC from Visual Basic Program. Please help me for this. I want to store image files. This is most urgent. Regards, A.Mohan _______________________________________________________________________ Odomos - the only mosquito protection outside 4 walls - Click here to know more! http://r.rediff.com/r?http://clients.rediff.com/odomos/Odomos.htm&&odomos&&wn
Here are two functions I wrote about two years ago to do this very thing. You will have to modify them to fit your needs, but it will give you a start. intGetPicture = SQLGetLargeObject("Student", "StudentID = " & strStudentID, "Picture", "C:\temppic.jpg", "select * from Student where StudentID = " & strStudentID) ' 0 = OK ' 1 = Error ' 2 = No piture available Function SQLGetLargeObject(strTableName As String, strThisRow As String, strField As String, strFile As String, strSQL As String) As Integer Dim rsFetch As ADODB.Recordset Dim intFileHandle As Integer Dim lngFileLength As Long Dim byteMemChunk() As Byte SQLGetLargeObject = 1 ' Open a recordset of the table Set rsFetch = New ADODB.Recordset With rsFetch '.Open strTableName, adoConnection, adOpenKeyset, adLockOptimistic, adCmdTable .Open strSQL, adoConnection, adOpenKeyset, adLockOptimistic, adCmdText .MoveFirst .Find strThisRow ' If the end of the recordset is reached then exit with error If .EOF = True Then rsFetch.Close Set rsFetch = Nothing 'SevereErrorMessage "Could not find the requested row when looking for a large object." Exit Function End If End With ' Get the length of the stored object lngFileLength = -1 lngFileLength = rsFetch.Fields(strField).ActualSize 'DebugShow "Size of blob:" & CStr(lngFileLength) ' Check to see if blob available If lngFileLength = 0 Then SQLGetLargeObject = 2 Exit Function End If ' Initialize the file where to store the blob intFileHandle = FreeFile Open strFile For Binary Access Write As intFileHandle ReDim byteMemChunk(1 To lngFileLength) ' Get it from the database byteMemChunk() = rsFetch.Fields(strField).GetChunk(lngFileLength) ' ... and store in the file Put intFileHandle, , byteMemChunk() ' Tidy up Close rsFetch.Close Set rsFetch = Nothing SQLGetLargeObject = 0 End Function strSQL = "update Student set Picture = ? where StudentID = " & Me.Tag If SQLPutLargeObject(strSQL, "Student", Me.picStudent.Tag) = False Then DebugShow "Could not update the student table with a new picture." bError = True End If Function SQLPutLargeObject(strSQL As String, strPlaceName As String, strFile As String) As Boolean Dim adoCommand As ADODB.Command Dim adoParmFile As ADODB.Parameter Dim intFileHandle As Integer Dim lngFileLength As Long Dim byteMemChunk() As Byte Dim lngRecordsAffected As Long Set adoCommand = New ADODB.Command SQLPutLargeObject = False ' Set up the command adoCommand.ActiveConnection = adoConnection adoCommand.CommandText = strSQL adoCommand.CommandType = adCmdText DebugShow strSQL ' Open the file for reading intFileHandle = FreeFile Open strFile For Binary Access Read As intFileHandle lngFileLength = LOF(intFileHandle) ' If file length is 0 then exit function If lngFileLength = 0 Then ' Tidy Up Close Set adoCommand = Nothing 'SevereErrorMessage "Could not open " & strFile Exit Function End If ' The fourth parameter indicates the memory to allocate to store the object Set adoParmFile = adoCommand.CreateParameter(strPlaceName, adLongVarBinary, adParamInput, lngFileLength + 100) ReDim byteMemChunk(1 To lngFileLength) Get intFileHandle, , byteMemChunk() ' Insert the object into the parameter object adoParmFile.AppendChunk byteMemChunk() adoCommand.Parameters.Append adoParmFile ' Now execute the command adoCommand.Execute lngRecordsAffected 'DebugShow "Records affected:" & lngRecordsAffected ' Tidy Up Set adoCommand = Nothing Close SQLPutLargeObject = True End Function -----Original Message----- I would like to know how to store and retrieve binary data in PostgreSQL thourgh ODBC from Visual Basic Program. Please help me for this. I want to store image files. This is most urgent.
Hello, Unfortunately you will probably need to build the large object extension in. In the source contrib directory there is a directory called lo. Below is the readme for this directory. If you read it, it will explain the problem (why oids don't work) and the solution. And of course how to install it. Don't forget to run the lo.sql script on the database in question. eg: For my installation, I found the directory at: /usr/src/postgresql-7.3.2/contrib/lo Hope that helps ... Mike. README.lo PostgreSQL type extension for managing Large Objects ---------------------------------------------------- Overview One of the problems with the JDBC driver (and this affects the ODBC driver also), is that the specification assumes that references to BLOBS (Binary Large OBjectS) are stored within a table, and if that entry is changed, the associated BLOB is deleted from the database. As PostgreSQL stands, this doesn't occur. It allocates an OID for each object, and it is up to the application to store, and ultimately delete the objects. Now this is fine for new postgresql specific applications, but existing ones using JDBC or ODBC wont delete the objects, arising to orphaning - objects that are not referenced by anything, and simply occupy disk space. The Fix I've fixed this by creating a new data type 'lo', some support functions, and a Trigger which handles the orphaning problem. The 'lo' type was created because we needed to differenciate between normal Oid's and Large Objects. Currently the JDBC driver handles this dilema easily, but (after talking to Byron), the ODBC driver needed a unique type. They had created an 'lo' type, but not the solution to orphaning. Install Ok, first build the shared library, and install. Typing 'make install' in the contrib/lo directory should do it. Then, as the postgres super user, run the lo.sql script. This will install the type, and define the support functions. How to Use The easiest way is by an example: > create table image (title text,raster lo); > create trigger t_image before update or delete on image for each row > execute procedure lo_manage(raster); Here, a trigger is created for each column that contains a lo type. Issues * dropping a table will still orphan any objects it contains, as the trigger is not actioned. For now, precede the 'drop table' with 'delete from {table}'. However, this could be fixed by having 'drop table' perform an additional 'select lo_unlink({colname}::oid) from {tablename}' for each column, before actually dropping the table. * Some frontends may create their own tables, and will not create the associated trigger(s). Also, users may not remember (or know) to create the triggers. This can be solved, but would involve changes to the parser. As the ODBC driver needs a permanent lo type (& JDBC could be optimised to use it if it's Oid is fixed), and as the above issues can only be fixed by some internal changes, I feel it should become a permanent built-in type. I'm releasing this into contrib, just to get it out, and tested. Peter Mount <peter@retep.org.uk> June 13 1998 -----Original Message----- There is no data type lo like you mentioned in PGSQL. O.K. Here I gave my table structure. Table name photo: ddocode varchar 5 treasurycode varchar 5 signature bytea photo1 bytea photo2 bytea some times instead of bytea, I have used oid also. >CREATE TABLE Student >( >StudentID integer NOT NULL, >Picture lo, >PRIMARY KEY( StudentID ) >); > >CREATE TRIGGER TRIGStudentPicture >BEFORE UPDATE OR DElETE >ON Student >FOR EACH ROW >EXECUTE PROCEDURE lo_manage(Picture); > >Make sure you are using the latest pgsql odbc driver from Hiroshi Inoue >site as well. -- Mike Miller, Computer Programmer, Department of Psychology, University Of Otago mike@psy.otago.ac.nz +64 3 479 5402 ...when you lay awake at night hoping that those elves from "The Elves and the Shoemaker" know where you work and can program in C++ as well as they can sew together sandles... -- stolen from (http://www.gameai.com/youknow.html)