Reviewing the Column Choices in SharePoint 2010 (part 2) - Leveraging Validation Settings & Enforcing Unique Values in Columns

Leveraging Validation Settings

Another means of ensuring that the correct data is entered into columns in a list and library is through the use of validation settings, which can be added to the list or library on the List Settings or Library Settings page, or to an individual column. The equations that can be used are more limited, as the result of the equation must equal the value True or the user won’t be able to save the entry.

A simple example is

=[ColumnA]>[ColumB]

Assuming the value in ColumnA is greater than ColumnB, the formula generates the value True and therefore passes the validation test.

Building on the list created in the previous section, follow these steps to add validation to the CalculatedColumnTest list:

1.	Navigate to the CalculatedColumnTest created in the previous section that contains the columns Title, Cost, and Sell Price, as described in the example, as well as sample data, as shown in Figure 22.6.
2.	Click the List tab on the Ribbon, and then click Create Column.
3.	Enter Invoice Number as the column name, and then choose Single Line of Text.
4.	Scroll down to the Description field and enter Enter a valid invoice number starting with "2010-" and then up to 4 digits.
5.	Click Enforce Unique Values.
6.	Enter 9 for Maximum Number of Characters.
7.	Expand the Column Validation section by clicking the + and enter the following in the Formula field: =FIND("2010-",[Invoice Number], 1) The FIND function is also defined in Excel 2010 Help, and the syntax translates to “FIND(find_text, within_text, [start_num]),” or in this example to “Find the string 2010- in the column Invoice Number, starting with the first character in the string and the value is True.” This logic is pretty hard for a careless or even malicious user to beat because there is a limit of nine characters that can be entered in the field and it must include the string 2010-. Furthermore, the entry must be unique.
8.	Finally, enter the following in the User Message field: You have entered an invalid invoice number (see Figure 2). Click OK to save. Figure 2. Column settings for a column using column validation.
9.	Click OK to the message stating: “This column must be indexed to enforce unique values. Do you want to index this column?”
10.	Click Add New Item and enter the title as Whoozit, the Cost as 100, the Sell Price as 150, and Invoice Number as 123456789. Click Save. A red error message will display, stating “The validation formula has evaluated to an error,” as shown in Figure 3, because this invoice number doesn’t meet the validation. Figure 3. Validation formula error for a New List item.
11.	Reenter the invoice number as 2010-123 and click Save; this time the entry succeeds because it meets the validation requirements.

Enforcing Unique Values in Columns

Certain column types offer the option to Enforce Unique Values for the column. This is a capability that has been requested by many clients over the years, and various workarounds were developed using workflows or leveraging the ID value of the list item. For example, a list that tracks serial numbers, employee IDs, invoices, or many other values will be less valuable if data entry errors can lead to nonunique numbers.

Table 1 summarizes what column types can and cannot be used to create unique columns.