Re: JDBC - PreparedStatement reuse oddity when using setObject() with nulls and setTimestamp()

Dave,

Apologies, it looks like there is a subtelty here which I didn't realise / didn't mention before, you have to insert 4 records first before you insert the null record. I have tested with the latest driver and can now constantly reproduce this, more detail below:

e.g. server statement level logging below: if you insert 3 records then a null then another timestamp:

LOG:  execute S_1: BEGIN
LOG:  execute <unnamed>: DELETE FROM test
LOG:  execute <unnamed>: INSERT INTO test (dt) VALUES ($1)
DETAIL:  parameters: $1 = '2013-02-20 22:44:14.237'
LOG:  execute <unnamed>: INSERT INTO test (dt) VALUES ($1)
DETAIL:  parameters: $1 = '2013-02-20 22:44:14.239'
LOG:  execute <unnamed>: INSERT INTO test (dt) VALUES ($1)
DETAIL:  parameters: $1 = '2013-02-20 22:44:14.24'
LOG:  execute <unnamed>: INSERT INTO test (dt) VALUES ($1)
DETAIL:  parameters: $1 = NULL
LOG:  execute S_2: INSERT INTO test (dt) VALUES ($1)
DETAIL:  parameters: $1 = '2013-02-20 22:44:14.241'
LOG:  execute S_3: COMMIT

All good there, now if you insert 4 records then a null then another timestamp:

LOG:  execute S_1: BEGIN
LOG:  execute <unnamed>: DELETE FROM test
LOG:  execute <unnamed>: INSERT INTO test (dt) VALUES ($1)
DETAIL:  parameters: $1 = '2013-02-20 22:44:21.154'
LOG:  execute <unnamed>: INSERT INTO test (dt) VALUES ($1)
DETAIL:  parameters: $1 = '2013-02-20 22:44:21.156'
LOG:  execute <unnamed>: INSERT INTO test (dt) VALUES ($1)
DETAIL:  parameters: $1 = '2013-02-20 22:44:21.157'
LOG:  execute <unnamed>: INSERT INTO test (dt) VALUES ($1)
DETAIL:  parameters: $1 = '2013-02-20 22:44:21.157'
LOG:  execute S_2: INSERT INTO test (dt) VALUES ($1)
DETAIL:  parameters: $1 = NULL
LOG:  execute S_2: INSERT INTO test (dt) VALUES ($1)
DETAIL:  parameters: $1 = '2013-02-20'
LOG:  execute S_3: COMMIT

And you see the time has gone, interesting to note that the it looks like this could be related to the statement numbers switching from "unnamed" to S_2? To be complete about this (and to find this subtelty) I used the following code in case you have trouble reproducing:

// quick imports
import java.sql.*;
import java.util.*;

// class to demonstrate postgresql timestamp issue with setnull
// using system out printlns so can be run independantly of any framework
public class DemoDateIssue
{
  // constants
  private static final String POSTGRESQL_DRIVER_CLASS = "org.postgresql.Driver";
  private static final String POSTGRESQL_CONNECTION_STRING = "jdbc:postgresql://host:5433/example";
  private static final String POSTGRESQL_USERNAME = "example";
  private static final String POSTGRESQL_PASSWORD = "example";

  // main method
  public static void main(String[] args)
  {
    // simple create and run
    (new DemoDateIssue()).demo();
  }

  // demo method
  public void demo()
  {
    // setup variables
    System.out.println("Starting demo process");
    Connection tCon = null;
    Statement tStmt = null;
    PreparedStatement tPStmt = null;

    // try block to clean up db afterwards
    try
    {
      // connect to database
      System.out.println("Connecting to database");
      Class.forName(POSTGRESQL_DRIVER_CLASS);
     
      Properties tProps = new Properties();
      tProps.put("user", POSTGRESQL_USERNAME);
      tProps.put("password", POSTGRESQL_PASSWORD);
      tCon = DriverManager.getConnection(POSTGRESQL_CONNECTION_STRING, tProps);

      // disable auto commits to ensure this is transactional
      tCon.setAutoCommit(false);

   
      // assuming a simple table with one timestamp field such as "CREATE TABLE test ( dt TIMESTAMP )"
     

      // create statement to clear down data
      tStmt = tCon.createStatement();
      tStmt.executeUpdate("DELETE FROM test");

     
      // prepare a statement on a postgresql connection

      tPStmt = tCon.prepareStatement("INSERT INTO test (dt) VALUES (?) ");

      // note: looks like you need to insert 4 dates first before the null to cause this issue
      Object tObject = null;

      // clear parameters, set timestamp to now and execute

      System.out.println("Inserting first timestamp");
      tPStmt.clearParameters();
      tObject = new Timestamp(System.currentTimeMillis());
      tPStmt.setTimestamp(1, (Timestamp)tObject);
      tPStmt.executeUpdate();

     
      // clear parameters, set timestamp to now and execute

      System.out.println("Inserting second timestamp");
      tPStmt.clearParameters();
      tObject = new Timestamp(System.currentTimeMillis());
      tPStmt.setTimestamp(1, (Timestamp)tObject);
      tPStmt.executeUpdate();

     
      // clear parameters, set timestamp to now and execute

      System.out.println("Inserting third timestamp");
      tPStmt.clearParameters();
      tObject = new Timestamp(System.currentTimeMillis());
      tPStmt.setTimestamp(1, (Timestamp)tObject);
      tPStmt.executeUpdate();

     
      // clear parameters, set timestamp to now and execute

      System.out.println("Inserting fourth timestamp");
      tPStmt.clearParameters();
      tObject = new Timestamp(System.currentTimeMillis());
      tPStmt.setTimestamp(1, (Timestamp)tObject);
      tPStmt.executeUpdate();

     
      // clear parameters, set using a null object and execute

      System.out.println("Inserting null object");
      tPStmt.clearParameters();
      tObject = null;
      tPStmt.setObject(1, tObject, Types.DATE);
      tPStmt.executeUpdate();

     
      // clear parameters, set timestamp to now and execute

      System.out.println("Inserting fifth timestamp (6th row)");
      tPStmt.clearParameters();
      tObject = new Timestamp(System.currentTimeMillis());
      tPStmt.setTimestamp(1, (Timestamp)tObject);
      tPStmt.executeUpdate();

     
      // this will output 6 rows assuming current date / time is 12/02/2013 17:08:01
      // 1st row = 12/02/2013 17:08:01

      // 2nd row = 12/02/2013 17:08:01
      // 3rd row = 12/02/2013 17:08:01
      // 4th row = 12/02/2013 17:08:01
      // 5th row = null
      // 6th row = 12/02/2013 00:00:00

      // if you only insert 3 rows before the null then it works just fine! !

     
      // as you can see the 3rd row has had its time wiped out and set to midnight
      // tested against various versions, last test against PostgreSQL 9.1.3 on linux 64 bit
      // and using JDBC PostgreSQL 9.2devel JDBC4 (build 1000)

      // commit to database
      System.out.println("Committing to database");
      tCon.commit();

      // success
      System.out.println("Demonstration code complete, check database for results");
    }
    catch (Exception tEx)
    {
      // bad practise to capture all exceptions but doing so for demonstrative purposes
      System.out.println("ERROR: An exception occurred whilst running database test, stack trace below");
      tEx.printStackTrace();
    }
    finally
    {
      // null check then close statements followed by connection
      if (tStmt != null) try { tStmt.close(); } catch (Exception tEx) { /* silent error in cleanup */ }
      if (tPStmt != null) try { tPStmt.close(); } catch (Exception tEx) { /* silent error in cleanup */ }
      if (tCon != null) try { tCon.close(); } catch (Exception tEx) { /* silent error in cleanup */ }
    }
  } 
}

-- 
Alastair Burr
Senior Engineer & Project Coordinator, Bluestar Software
Telephone: +44 (0)1256 882695
Web site: www.bluestar-software.co.uk
Email: alastair.burr@bluestar-software.co.uk

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