[OS-JIRA] Created: (CAY-115) Using DISTINCT when joining on to-many sometimes causes trouble

From: jir..bjectstyle.org
Date: Mon Apr 05 2004 - 00:36:06 EDT

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A new issue has been created in JIRA.

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http://objectstyle.org/jira/secure/ViewIssue.jspa?key=CAY-115

Here is an overview of the issue:
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        Key: CAY-115
    Summary: Using DISTINCT when joining on to-many sometimes causes trouble
       Type: Bug

Status: Assigned
Priority: Minor

    Project: Cayenne
Components:
             Cayenne Core Library
   Fix Fors:
             1.1 [DEV]
   Versions:
             1.0 [STABLE]
             1.1 [DEV]

Assignee: Andrus Adamchik
Reporter: Andrus Adamchik

Created: Mon, 5 Apr 2004 12:35 AM
Updated: Mon, 5 Apr 2004 12:35 AM
Environment: MS SQL Server, "text" columns

Description:
Originally reported by Bill Fan:

SQL Server blows with exception "[Microsoft][SQLServer 2000 Driver for JDBC][SQLServer]The text, ntext, or image data type cannot be selected as DISTINCT." when a DISTINCT is automatically added to the SELECT statement when joining on to-many.

Possible fixes require either subquery support in translators (might be a good alternative fetch strategy in general), or doing "distinct" on ObjectId in-memory when processing result.

The last strategy is hard to implement efficienly (skipping duplicate ResultSet rows without fully reading them)... The only implementation that comes to mind is actually building ObjectId out of every row and using a map in SelectObserver to verify that a give ID is not yet in the map.

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