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List:       sqlite-users
Subject:    [sqlite] Jdbc & Blob & Incremental I/O
From:       gwenn <gwenn.kahz () gmail ! com>
Date:       2012-08-26 16:06:23
Message-ID: CAMUyzFCWRGj-5uzsaQ1ADeRFk+V6ryCDmPxVoV_PegZcrAzv-A () mail ! gmail ! com
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Hi,
I've been trying to support incremental I/O in a Jdbc driver.
By forcing the user to access the rowid before the blob, it's possible
to use only the JDBC API for loading a Blob:
    // CREATE TABLE test (data BLOB); INSERT INTO test (data) VALUES
(zeroblob(1024));
    ResultSet rs = stmt.executeQuery("SELECT rowid, data FROM test");
    rs.getRowId(1);
    final Blob blob = rs.getBlob(2);
    ...
Indeed, with the rowId kept internally by the driver and with the
column index (2), I can retrieve all the data needed by
'sqlite3_blob_open': dbName, tblName, colName.
I will also support this alternative:
    PrepareStatement pstmt = c.prepareStatement("SELECT data FROM test
where rowid = :rowid");
    pstmt.setRowId(1, ...); -- rowId value kept internally
    ResultSet rs = pstmt.executeQuery();
    final Blob blob = rs.getBlob(1);

But for update/insert, it doesn't work because the
sqlite3_column_name, sqlite3_column_origin_name,
sqlite3_column_table_name and sqlite3_column_database_name can only be
used with select:
    PreparedStatement pstmt = c.prepareStatement("UPDATE test SET data
= :blob WHERE rowid = :rowid");
    pstmt.setRowId(2, new RowIdImpl(rowid));
    pstmt.setBinaryStream(1, new ByteArrayInputStream(new byte[] {1,
2, 3, 4, 5, 6})); -- fails
    pstmt.executeUpdate();

Do you see a way to write a blob incrementally by using only the JDBC API?
(I've checked all the other implementations, but they don't support
reading, nor writing...)

Thanks.

(the driver is here:
https://github.com/gwenn/sqlite-jna/tree/master/src/main/java/org/sqlite/driver)
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