Unique-valued fields Registry entries

EMu provides two different Registry entries for specifying the uniqueness of fields, the Unique Registry entry and the Unique Index Registry entry. Both of these entries can be used to specify uniqueness, but there are differences between the two:

Unique

Specifies that a column or a combination of columns must be unique in order to save a record, and a message to be displayed if uniqueness is violated:

  • This is a client-side entry and uniqueness is checked when the record is saved. If a field or a combination of fields required to be unique is not unique, the record is not saved and the message displays warning the user to change the value.
  • This setting can be overridden using a Unique Override Registry entry (users / groups are able to save a record even if a Unique Registry entry specifies that a column or a combination of columns must be unique in order to save a record and the column or combination of columns is not unique).

Unique Index

Specifies that one or more columns is unique:

  • This is a server-side entry and uniqueness is checked as focus leaves the field. If the field contains a non-unique value, a generic system warning message displays indicating that the value is not unique.
  • This setting can be overridden using a Unique Strict Registry entry (specifies users / groups able to save a record even if a field that has been configured on the server to be unique is not unique).
  • The Unique Index Registry entry was introduced with EMu 4.1 to allow Administrators to specify server-side uniqueness of one or more columns, which is necessary when enabling uniqueness checking and auto-incrementation of a value in a field. See Uniqueness checking and auto-incrementation for details. Previously it was necessary to request EMu Support to set server-side uniqueness on a column.

In general, unless you are looking to enable uniqueness checking and auto-incrementation of a value in a field, it is recommended that you use the Unique Registry entry to specify the uniqueness of columns.

With the Unique Registry entry it is possible to specify that a combination of columns is unique in order to save a record. For example, if a unique combination of three columns is required to save a record, two records can share two of the three values, as long as the third value is different. If the combination of Field1, Field2, and Field3 must be unique, these two records could be saved:

Record 1: Field1 = A, Field2 = B, Field3 = C

Record 2: Field1 = A, Field2 = B, Field3 = D

But this record could not be saved:

Record 3: Field1 = A, Field2 = B, Field3 = C

With the Unique Index Registry entry it is possible to specify that one or more columns is unique but it is not possible to specify that a combination of columns is unique. For example, it is possible to specify that Field1, Field2, and Field3 must be unique in order to save a record but not that the combination of Field1 +Field2 +Field3 must be unique. No two records can share the same value in Field1, Field2 or Field3. For example, if Field1, Field2 and Field3 are defined as unique with a Unique Index Registry entry and Record 1 contains:

Field1 = A, Field2 = B, Field3 = C

Record 2 could not be saved if even one of the three fields has the same value as in Record 1. All three fields must be unique.