MACROMEDIA COLDFUSION MX 61-DEVELOPING COLDFUSION MX, Develop Manual

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566 Chapter 26: Retrieving and Formatting Data
Reviewing the code
The following table describes the highlighted code and its function:
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 CFML Reference .
The following code prevents the error in the previous example by checking to see if the
Contractor Form variable exists before using it:
<cfif IsDefined("Form.Contractor")>
<cfoutput>Contractor: #Form.Contractor#</cfoutput>
</cfif>
The argument passed to the
IsDefined
function must always be enclosed in double quotation
marks. For more information on the
IsDefined
function, see 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 MX 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 a particularly important requirement for database applications, ColdFusion provides a
server-side mechanism for requiring users to enter data in fields.
Code Description
<cfquery name="GetEmployees"
datasource="CompanyInfo"> Queries the data source CompanyInfo and names the
query GetEmployees.
SELECT FirstName, LastName, Salary
FROM Employee
WHERE LastName=<cfqueryparam
value="#Form.LastName#"
CFSQLType="CF_SQL_VARCHAR">
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.
<cfoutput query="GetEmployees"> Displays results of the GetEmployees query.
#FirstName#
#LastName#
#Salary#<br> 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.
</cfoutput>
Closes the
cfoutput
block.
<br>
<cfoutput>Contractor: #Form.Contractor#
</cfoutput>
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.