SPListConstraints is a list constraints feature for SharePoint 2007 & WSS 3. The feature includes several list constraint the user can put on the list.

• Unique key constraint: Restrict field (or multiple fields) value to be unique (like SQL unique index).
• Foreign key constraint: Restrict field (or multiple fields) value to values that already exist in another list (like SQL foreign key).
• Data validation constraint: Restrict field value in relation to other fields (e.g. Name = Title). Supported field types: Number, Date, Currency (all other fields will be compared as string).
• Maximal items count contraint: Restrict the number of items allowed in the list.
• Format validation constraint: Restrict field value to fit a regular expression.
• Special flags:
  • Require check-in comment

• Server: Windows SharePoint Services 3.0 (WSS 3.0 or SharePoint 2007)

• Workflows - If a workflow action changes list data so it overrides a constraint - the constraint enforcement will cause the workflow to return an error.
• Upgrade - If after upgrading SPListConstraints the constraints are not enforced - Enable/Disable the SPListContraints feature.
• Footprint - Settings of SPListContraints are deleted only when the users removes the constraints. The settings will not be removed on feature Activate/Deactivate (this is done to allow smoother upgrade).
• Unique Key constraint: when updating an item, if there was a duplication before the item was editted, the constraint will not be enforced (it will be enforced if one of the fields of the contraint will be changed in the item).
• Unique Key constraint: always enforced on all the folders in the list

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