101 lines
6.5 KiB
HTML
101 lines
6.5 KiB
HTML
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<!DOCTYPE html
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Enable or disable referential constraints" />
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<meta name="abstract" content="You can enable or disable a referential constraint using the Change Physical File Constraint (CHGPFCST) command or iSeries Navigator." />
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<meta name="description" content="You can enable or disable a referential constraint using the Change Physical File Constraint (CHGPFCST) command or iSeries Navigator." />
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<title>Enable or disable referential constraints</title>
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</head>
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<body id="rbaforzahfrcy"><a name="rbaforzahfrcy"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Enable or disable referential constraints</h1>
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<div><p>You can enable or disable a referential constraint using the Change
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Physical File Constraint (CHGPFCST) command or iSeries™ Navigator.</p>
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<p>To enable or disable a referential constraint relationship, use the CHGPFCST
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command. You must specify the dependent file when changing a referential constraint;
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you cannot disable or enable a constraint by specifying the parent file.</p>
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<p>You can also enable or disable a referential constraint using iSeries Navigator. </p>
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<p>You must have a minimum of object management authority (or ALTER privilege)
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to the dependent file in order to enable or disable a constraint.</p>
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<div class="section" id="rbaforzahfrcy__rbaforzahfrcz"><a name="rbaforzahfrcy__rbaforzahfrcz"><!-- --></a><h4 class="sectiontitle">Details: Enable or disable referential
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constraints</h4><p>When the system enables or disables a constraint, it
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locks the parent and the dependent files, both members, and both access paths.
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It removes the locks when the enable or disable operation is complete.</p>
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<p>Attempting
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to enable an enabled constraint or disable a disabled constraint does nothing
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but cause the issuance of an informational message.</p>
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<p>An established/disabled
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or check pending constraint relationship can be enabled. The enabling causes
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the system to verify the constraint again. If verification finds mismatches
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between the parent and the foreign keys, the constraint is marked as check
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pending.</p>
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<p>Disabling a constraint relationship allows all file input/output
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(I/O) operations for both the parent and the dependent files, if the user
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has the correct authority. The entire infrastructure of the constraint remains.
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The parent key and the foreign key access paths are still maintained. However,
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there is no referential enforcement that is performed for the two files in
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the disabled relationship. All remaining enabled constraints are still enforced.</p>
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<div class="p">Disabling
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a constraint can allow file I/O operations in performance-critical situations
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to run faster. Always consider the trade-off in this kind of a situation.
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The file data can become referentially not valid. When the constraint is enabled,
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depending on the file size, the system will take time to re-verify the referential
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constraint relationship. <div class="note"><span class="notetitle">Note:</span> Users and applications must be cautious when
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modifying files with a constraint relationship in the established and disabled
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state. Relationships can be violated and not detected until the constraint
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is enabled again.</div>
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</div>
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<p>The Allocate Object (ALCOBJ) command can allocate
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(lock) files while a constraint relationship is disabled. This allocation
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prevents others from changing the files while this referential constraint
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relationship is disabled. Specify a lock state of Exclusive read (*EXCLRD)
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on the command so other users can read the files. After the constraint is
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enabled again, the Deallocate Object (DLCOBJ) command unlocks the files.</p>
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<p>When
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you enable or disable multiple constraints, they are processed sequentially.
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If a constraint cannot be modified, you receive a diagnostic message, and
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the function proceeds to the next constraint in the list. When all constraints
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have been processed, you receive a completion message listing the number of
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constraints modified.</p>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbaforzahfrca.htm" title="These topics discuss how to use referential constraints in your database to ensure that it contains only valid data.">Ensure data integrity with referential constraints</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="../rzatc/rzatcgetstartinav.htm">Get started with iSeries Navigator</a></div>
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<div><a href="../sqlp/rbafykickoff.htm">SQL programming</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="../cl/chgpfcst.htm">Change Physical File Constraint (CHGPFCST) command</a></div>
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<div><a href="../cl/alcobj.htm">Allocate Object (ALCOBJ) command</a></div>
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<div><a href="../cl/dlcobj.htm">Deallocate Object (DLCOBJ) command</a></div>
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</div>
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</div>
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</body>
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</html> |