Adobe ColdFusion 8

Defining and using method parameters

You pass data to a method by using parameters. To define a component method parameter, use the cfargument tag in the cffunction tag body. To define multiple parameters, use multiple cfargument tags. The tag names a parameter and lets you specify the following:

  • Whether the parameter is required
  • The type of data that is required
  • A default argument value
  • Display name and hint metadata for CFC introspection

Note: You can create CFC methods that do not use cfargument tags, for example, if you use positional parameters in your methods. However, most CFC methods use the cfargument tag.

Example: convertTemp.cfc

The convertTemp.cfc file consists of the following:

<cfcomponent>
    <!--- Celsius to Fahrenheit conversion method. --->
    <cffunction name="ctof" output="false">
        <cfargument name="temp" required="yes" type="numeric">
        <cfreturn ((temp*9)/5)+32>
    </cffunction>

    <!--- Fahrenheit to Celsius conversion method. --->
    <cffunction name="ftoc" output="false">
        <cfargument name="temp" required="yes" type="numeric">
        <cfreturn ((temp-32)*5/9)>
    </cffunction>
</cfcomponent>

Reviewing the code

The convertTemp CFC contains two methods that convert temperature. The following table describes the code and its function:

Code

Description

<cfcomponent>

Defines the component.

<cffunction name="ctof" output="false">

Defines the ctof method.

Indicates that this method does not display output.

<cfargument name="temp" required="yes" type="numeric">

Creates the temp parameter of the ctof method. Indicates that it is required and that the expected value is numeric.

<cfreturn ((temp*9)/5)+32>

Defines the value that the method returns.

</cffunction>

Ends the method definition.

<cffunction name="ftoc" output="false">

Defines the ftoc method.

Indicates that this method does not display output.

<cfargument name="temp" required="yes" type="numeric">

Creates the temp parameter of the ftoc method. Indicates that it is required and that the expected value is numeric.

<cfreturn ((temp-32)*5/9)>

Defines the value that the method returns.

</cffunction>

Ends the method definition.

</cfcomponent>

Ends the component definition.

Example: tempConversion.cfm

The ColdFusion page tempConversion.cfm is an HTML form in which the user enters the temperature to convert, and selects the type of conversion to perform. When the user clicks the Submit button, ColdFusion performs the actions on the processForm.cfm page. The file tempConversion.cfm, which should be in the same directory as convertTemp.cfc, consists of the following:

<cfform action="processForm.cfm" method="POST">
    Enter the temperature:
        <input name="temperature" type="text"><br><br>
    Select the type of conversion:<br>
        <select name="conversionType">
            <option value="CtoF">Celsius to Farenheit</option>
            <option value="FtoC">Farenheit to Celsius</option>
        </select><br><br>
    <input name="submitform" type="submit" value="Submit">
</cfform>

Example: processForm.cfm

The ColdFusion page processForm.cfm calls the appropriate component method, based on what the user entered in the form on the tempConversion.cfm page. It should be in the same directory as convertTemp.cfc.

<cfif #form.conversionType# is "CtoF">
    <cfinvoke component="convertTemp" method="ctof" returnvariable="newtemp"
        temp=#form.temperature#>
    <cfoutput>#form.temperature# degrees Celsius is #newtemp# degrees
        Farenheit.</cfoutput>
    <cfelseif #form.conversionType# is "FtoC">
        <cfinvoke component="convertTemp" method="ftoc"
            returnvariable="newtemp" temp=#form.temperature#>
        <cfoutput>#form.temperature# degrees Fahrenheit is #newtemp# degrees
            Celsius.</cfoutput>
</cfif>

Reviewing the code

The file processForm.cfm invokes the appropriate component method. The following table describes the code and its function:

Code

Description

<cfif form.conversionType is "CtoF">

Executes the code in the cfif block if the user selected Celsius to Fahrenheit as the conversion type in the form on the tempConversion.cfm page.

<cfinvoke component="convertTemp" method="ctof" returnvariable="newtemp" arguments.temp="#form.temperature#">

Invokes the ctof method of the convertTemp component, without creating an instance of the convertTemp component. Specifies newtemp as the result variable for the method. Assigns the temperature value that the user entered in the form to the variable temp, which is specified in the cfargument tag of the ctof method. When invoking the ctof method, the temp variable is assigned to the Arguments scope. For more information about variables and scope, see CFC variables and scope.

<cfoutput>#form.temperature# degrees Celsius is #newtemp# degrees Fahrenheit.</cfoutput>

Displays the temperature that the user entered in the form, the text "degrees Celsius is," the new temperature value that results from the ctof method, and the text "degrees Fahrenheit."

<cfelseif #form.conversionType# is "FtoC">

Executes the code in the cfelseif block if the user selected Fahrenheit to Celsius as the conversion type in the form on the tempConversion.cfm page.

<cfinvoke component="converttemp" method="ftoc" returnvariable="newtemp" temp=#form.temperature#>

Invokes the ftoc method of the convertTemp component, without creating an instance of the convertTemp component. Specifies newtemp as the result variable for the method. Assigns the temperature value that the user entered in the form to the variable temp, which is specified in the cfargument tag of the ftoc method. When invoking the ftoc method, the temp variable is assigned to the Arguments scope. For more information about variables and scope, see CFC variables and scope.

<cfoutput>#form.temperature# degrees Fahrenheit is #newtemp# degrees Celsius.</cfoutput>

Displays the temperature that the user entered in the form, the text "degrees Fahrenheit is," the new temperature value that results from the ftoc method, and the text "degrees Celsius."

</cfif>

Closes the cfif block.

To run the example, display the tempConversion.cfm page in your browser. When you enter a value in the text box of the form, the value is stored in the form.temperature variable. Processing is then performed on the processForm.cfm page, which refers to the value as form.temperature. When you invoke either method, the cfinvoke tag assigns the value form.temperature to temp; temp is the argument specified in the cfargument tag of the appropriate method. The appropriate method in the convertTemp component performs the necessary calculations and returns the new value as newtemp.

For detailed reference information on the cfargument tag, see the CFML Reference.

To access the parameter values in the component method definition, use structure- or array-like notation with the Arguments scope. The following example refers to the lastName argument as Arguments.lastname; it could also refer to it as Arguments[1]. In addition, you can access arguments directly using number (#) signs, such as #lastname#; however, it is better programming practice to identify the scope (for example, #Arguments.lastname#). Also, you can use Array- or structure-like notation, which lets you loop over multiple parameters.

For more information on the Arguments scope, see The Arguments scope.

Define parameters in the component method definition

  1. Create a new component with the following contents, and save it as corpQuery.cfc in a directory under your web root directory:
    <cfcomponent>
        <cffunction name="getEmp">
            <cfargument name="lastName" type="string" required="true" 
                    hint="Employee last name">
            <cfset var empQuery="">
             <cfquery name="empQuery" datasource="cfdocexamples">
                 SELECT LASTNAME, FIRSTNAME, EMAIL
                 FROM tblEmployees
                WHERE LASTNAME LIKE '#Arguments.lastName#'
             </cfquery>
                <!--- Use cfdump for debugging purposes. --->
             <cfdump var=#empQuery#>
        </cffunction>
        <cffunction name="getCat" hint="Get items below specified cost">
        <cfargument name="cost" type="numeric" required="true">
            <cfset var catQuery="">
            <cfquery name="catQuery" datasource="cfdocexamples">
                 SELECT ItemName, ItemDescription, ItemCost
                 FROM tblItems
                WHERE ItemCost <= #Arguments.cost#
             </cfquery>
                <!--- Use cfdump for debugging purposes. --->
             <cfdump var=#catQuery#>
        </cffunction>
    </cfcomponent>
    

In the example, the cfargument attributes specify the following:

  • The name attributes define the parameter names.
  • The type attribute for the lastName argument specifies that the parameter must be a text string. The type attribute for the cost argument specifies that the parameter must be a numeric value. These attributes validate the data before it is submitted to the database.
  • The required attributes indicate that the parameters are required or an exception will be thrown.
  • The Arguments scope provides access to the parameter values.