Adobe 38043740 Developing Applications - Page 714

DEVELOPING COLDFUSION 9 APPLICATIONS 709 Requesting and Presenting Information Code #FirstName# #LastName# #Salary# Contractor: #Form.Contractor# Description Displays the value of the FirstName, LastName, and Salary fields for a record, starting with the first record, then goes to the next line. Keeps displaying the records that match the criteria you specified in the SELECT statement, followed by a line break, until you run out of records. Closes the cfoutput block. Displays a blank line followed by the text "Contractor": and the value of the form Contractor check box. A more complete example would test to ensure the existence of the variable and would use the variable in the query. Testing for a variable's existence Before relying on a variable's existence in an application page, you can test to see if it exists using the ColdFusion IsDefined function. A function is a named procedure that takes input and operates on it. For example, the IsDefined function determines whether a variable exists. CFML provides a large number of functions, which are documented in the CFML Reference. The following code prevents the error in the previous example by checking to see whether the Contractor Form variable exists before using it: Contractor: #Form.Contractor# The argument passed to the IsDefined function must always be enclosed in double-quotation marks. For more information on the IsDefined function, see the CFML Reference. If you attempt to evaluate a variable that you did not define, ColdFusion cannot process the page and displays an error message. To help diagnose such problems, turn on debugging in the ColdFusion Administrator. The Administrator debugging information shows which variables are being passed to your application pages. Requiring users to enter values in form fields One of the limitations of HTML forms is the inability to define input fields as required. Because this is an important requirement for database applications, ColdFusion lets you require users to enter data in fields. To specify a field as required, you can do either of the following: • Use the required attribute of the cfinput, cfselect, cftextarea, and cftree tags. • Use a hidden field that has a name attribute composed of the field name and the suffix _required. You can use this technique with CFML and HTML form tags. For example, to require that the user enter a value in the FirstName field of a cfinput tag, use the following syntax: To require that the user enters a value in the FirstName field of an HTML input tag, use the following syntax: In either of these examples, if the user leaves the FirstName field empty, ColdFusion rejects the form submittal and returns a message informing the user that the field is required. You can customize the contents of this error message. If you use a required attribute, you customize the message by using the message attribute, as follows: Last updated 1/20/2012