When the user submits a form, ColdFusion runs the action page specified by the cfform or form tag action attribute. A ColdFusion action page is like any other application page, except that you can use the form variables that are passed to it from an associated form.
Processing form variables on action pages
The action page gets a form variable for every form control that contains a value when the form is submitted.
Note: If multiple controls have the same name, one form variable is passed to the action page with a comma-delimited list of values. |
A form variable's name is the name that you assigned to the form control on the form page. Refer to the form variable by name within tags, functions, and other expressions on an action page.
On the action page, the form variables are in the Form scope, prefix them with "Form." to explicitly tell ColdFusion that you are referring to a form variable. For example, the following code references the LastName form variable for output on an action page:
<cfoutput> |
The Form scope also contains a list variable called Form.fieldnames. It contains a list of all form variables submitted to the action page. If no form variables are passed to the action page, ColdFusion does not create the Form.fieldnames list.
Using form data to generate SQL statements
As described in previous chapters, you can retrieve a record for every employee in a database table by composing a query like the following:
<cfquery name="GetEmployees" datasource="cfdocexamples"> |
When you want to return information about employees that matches user search criteria, you use the SQL WHERE clause with a SQL SELECT statement. When the WHERE clause is processed, it filters the query data based on the results of the comparison.
For example, to return employee data for only employees with the last name of Smith, you build a query that looks like the following:
<cfquery name="GetEmployees" datasource="cfdocexamples"> |
However, instead of placing the LastName directly in the SQL WHERE clause, you can use the text that the user entered in the form for comparison:
<cfquery name="GetEmployees" datasource="cfdocexamples"> |
For security, this example encapsulates the form variable within the cfqueryparam tag to ensure that the user passed a valid string value for the LastName. For more information on using the cfqueryparam tag with queries and on dynamic SQL, see Accessing and Retrieving Data.
Creating action pages
Use the following procedure to create an action page for the formpage.cfm page that you created in the previous example.
Create an action page for the form
Create a ColdFusion page with the following content:
<html>
<head>
<title>Retrieving Employee Data Based on Criteria from Form</title>
</head>
<body>
<cfquery name="GetEmployees" datasource="cfdocexamples">
SELECT FirstName, LastName, Salary
FROM Employee
WHERE LastName=<cfqueryparam value="#Form.LastName#"
CFSQLType="CF_SQL_VARCHAR">
</cfquery>
<h4>Employee Data Based on Criteria from Form</h4>
<cfoutput query="GetEmployees">
#FirstName#
#LastName#
#Salary#<br>
</cfoutput>
<br>
<cfoutput>Contractor: #Form.Contractor#</cfoutput>
</body>
</html>- Save the page as actionpage.cfm in the myapps directory.
- View the formpage.cfm page in your browser.
- Enter data, for example, Smith, in the Last Name box and submit the form.The browser displays a line with the first and last name and salary for each entry in the database that match the name you typed, followed by a line with the text "Contractor: Yes".
- Click Back in your browser to redisplay the form.
- Remove the check mark from the check box and submit the form again. This time an error occurs because the check box does not pass a variable to the action page. For information on modifying the actionpage.cfm page to fix the error, see Testing for a variable's existence below.
Reviewing the code
The following table describes the highlighted code and its function:
Code |
Description |
|
|---|---|---|
|
Queries the data source cfdocexamples and names the query GetEmployees. |
|
|
Retrieves the FirstName, LastName, and Salary fields from the Employee table, but only if the value of the LastName field matches what the user entered in the LastName text box in the form on formpage.cfm. |
|
|
Displays results of the GetEmployees query. |
|
|
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:
<cfif IsDefined("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:
<cfinput type="Text" name="FirstName" size="20" maxlength="35" required="Yes"> |
To require that the user enters a value in the FirstName field of an HTML input tag, use the following syntax:
<input type="Text" name="FirstName" size="20" maxlength="35"> |
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:
<cfinput type="Text" name="FirstName" size="20" maxlength="35" required="Yes" |
If you use a hidden field tag, you customize the message using the value attribute of the hidden field, as follows:
<input type="hidden" name="FirstName_required" |
Form variable notes and considerations
When using form variables in an action page, keep in mind the following guidelines:
- A form variable is available on the action page and pages that it includes.
- Prefix form variables with "Form."__when referencing them on the action page.
- Surround variable values with number signs (#) for output.
- Variables for check boxes, radio buttons, and list boxes with size attributes greater than 1 only get passed to the action page if you select an option. Text boxes, passwords, and text area fields pass an empty string if you do not enter text.
- An error occurs if the action page tries to use a variable that was not passed.
- If multiple controls have the same name, one form variable is passed to the action page with a comma-delimited list of values.
- You can validate form variable values on the client or the server.