Reference : Attribute types : Unique ID
  
Unique ID
The unique ID attribute is similar to the text attribute; the attribute values are edited and stored in the same way. The difference between the unique ID and text attributes is that the values in a unique ID attribute are unique: two elements in the same module cannot have the same value for the attribute.
In the attribute editor:
▪ If Allow Editing is cleared, you cannot edit the attribute value after the element is created.
▪ If Allow Empty Values is selected, any number of elements can have an empty string as their attribute value.
▪ If Apply to Folders is selected, the unique ID attribute is treated the same way for all elements in the module (both folders and nodes). If this check box is cleared, the attribute is treated as a normal text attribute for the folders: the attribute values for folders have no restrictions.
You can reset the counter for unique ID using the Settings > Configure > Attributes option in the Modules view.
Unique ID settings
A unique ID attribute contains a value that is unique for an element. When an element with this attribute is created, the element is automatically assigned a unique ID. Typically, the unique ID is not editable.
 
Setting
Name and description
Value
You can configure the following settings:
▪ Default Value: The value of the unique ID attribute when a new element is added. You can edit this value before the element is saved.
– You can include the number sign (#) in the default value. The number sign (#) is replaced by an integer that makes the attribute value unique when an element is created.
– If the default value does not contain the number sign (#), a number sign (#) is added automatically to ensure that attribute values for new elements are unique.
– If the default value field is empty and the Allow Empty Values check box is selected, the number sign (#) is not added.
– You can use more than one number sign (#). If the default value is four number signs (####), when elements are created, the number signs are replaced with 0001, 0002, 0003, and so on.
▪ Allow Editing: Enables the unique ID attribute to be edited after the ID is created.
▪ Allow Empty Values: Select this check box to allow empty values. When the unique ID attribute is editable, the unique ID might be empty.
▪ Apply to Folders: If this check box is selected, the unique ID affects folders and elements.
Visual
You can configure the following settings:
▪ Prefix: The text to be displayed before the text value
▪ Suffix: The text to be displayed after the text value
Change Log
You can configure the following setting:
▪ Log Changes: Records each change of the attribute value.
Button
You can configure the following setting:
▪ Reset ID: Resets the unique ID attribute counter. The next element that is created is given the first available ID, which is the lowest value that is not in use for any element.
See also
Attribute types