OpenJPA
  1. OpenJPA
  2. OPENJPA-564

Set correct DBDictionary properties for MySQL based on MySQL version

    Details

    • Type: Improvement Improvement
    • Status: Closed
    • Priority: Minor Minor
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 1.1.0
    • Component/s: jdbc
    • Labels:
      None
    • Environment:
      Microsoft Windows XP SP2, Java version = 1.5.0 with MySQL 5.x Database.

      Description

      MySQL has many improvements since version 4.1. We should update default values of MySQLDictionary properties to reflect these changes. Ideally we should be able to set these properties correctly based on MySQL version, so the users don't need override "openjpa.jdbc.DBDictionary" property in persistence.xml.

      These properties include:
      1) DriverDeserializesBlobs (current default value: true)
      We added this flag to MySQLDictionary in Kodo4.1 since most MySQL drivers then automatically deserialized BLOBs on calls to ResultSet.getObject. This is actually a bug in MySQL, and that bug(#25328 in MySQL bug database) is already fixed in 5.x driver. Please see http://dev.mysql.com/doc/refman/5.1/en/cj-news-5-0-6.html for details.

      2) SupportSubselect (current default value: false)
      MySQL supports sub-select since version 4.1.

      3) AllowsAliasInBulkClause (current default value: false)
      This property is only used in DBDictionary.toBulkOperation():
      line 1874:
      // if there is only a single table in the select, then we can
      // just issue a single DELETE FROM TABLE WHERE <conditions>
      // statement; otherwise, since SQL doesn't allow deleting
      // from one of a multi-table select, we need to issue a subselect
      // like DELETE FROM TABLE WHERE EXISTS
      // (SELECT 1 FROM TABLE t0 WHERE t0.ID = TABLE.ID); also, some
      // databases do not allow aliases in delete statements, which
      // also causes us to use a subselect
      if (sel.getTableAliases().size() == 1 && supportsSubselect
      && allowsAliasInBulkClause) {
      SQLBuffer from;
      if (sel.getFromSelect() != null)
      from = getFromSelect(sel, false);
      else
      from = getFrom(sel, false);

      sql.append(from);
      appendUpdates(sel, store, sql, params, updateParams,
      allowsAliasInBulkClause);

      SQLBuffer where = sel.getWhere();
      if (where != null && !where.isEmpty())

      { sql.append(" WHERE "); sql.append(where); }

      return sql;
      }

      It confuses me why we need this property (and supportsSubselect) as conditions for single table update/delete. I believe we can set this property to true if we use MySQL version 4.1 or later. Otherwise If we set supportSubselect to true, we will run into problems described in
      http://issues.apache.org/jira/browse/OPENJPA-459. Note Patrick had a comment for that issue:
      "I believe that the first query (which only involves one table) is due to a fairly trivial-to-resolve limitation of DBDIctionary: currently, if SupportsSubselect is true and AllowsAliasInBulkClause is false, OpenJPA always uses a subselect, even when it would be valid to just omit the aliases."

        Issue Links

          Activity

          Jason Zheng created issue -
          Jason Zheng made changes -
          Field Original Value New Value
          Attachment openjpa-1.1.0-634377.patch [ 12379701 ]
          Jason Zheng made changes -
          Resolution Fixed [ 1 ]
          Status Open [ 1 ] Resolved [ 5 ]
          Fix Version/s 1.1.0 [ 12312344 ]
          Michael Dick made changes -
          Resolution Fixed [ 1 ]
          Status Resolved [ 5 ] Reopened [ 4 ]
          Abe White made changes -
          Resolution Fixed [ 1 ]
          Status Reopened [ 4 ] Resolved [ 5 ]
          Milosz Tylenda made changes -
          Link This issue is related to OPENJPA-883 [ OPENJPA-883 ]
          Donald Woods made changes -
          Status Resolved [ 5 ] Closed [ 6 ]

            People

            • Assignee:
              Unassigned
              Reporter:
              Jason Zheng
            • Votes:
              0 Vote for this issue
              Watchers:
              0 Start watching this issue

              Dates

              • Created:
                Updated:
                Resolved:

                Development