Dynamically Accessing Implicit Getters Using Script In ColdFusion 9

I was recently working on a project where I needed to call a getter dynamically. If your not quite sure what I am talking about that is perfectly fine because we are going to walk through it. I needed the ability to get all of the properties of any component passed to me, then loop those properties and one by one get the values of that property by calling the getter method on that property. Another reason for this post is because I found 2 different ways to accomplish this based on how you do it. With that I want to walk through some cocde that shows both methods.

The first method achieving our goal is if we are trying to access the values outside of our component. What I mean by that is if we were to create in instance of our class and then loop over the properties how could we get those values. It turns out it was pretty easy to do just that. First we need to take a look at our very basic user object. component accessors="true" { property userid; property firstname; property lastname; } With our component in place we can create an instance of it and set our property values by calling each set method. user = new User(); user.setUserId(10); user.setFirstName("Dan"); user.setLastName("Vega"); Next we need a way of dynamically grabbing a list of all the properties in the component. We can accomplish this by grabbing the components meta data. properties = getMetaData(user).properties; Finally we loop over the array of properties and print the key and value. To dnamically call the getter you can use the evaluate method. This is easier if you are using tags because you can just use cfinvoke. I don't know, maybe it's just me but neither seem like the "right" way to do it but it works! for(i=1; i <= arrayLen(properties); i++){ property = properties[i]; writeOutput( property.name & ":" & evaluate("user." & "get#property.name#()") & "<br/>"); }

The next method is going to be within our component. Maybe we want to create a method that would return each key/value for all the properties in our component. We could write each one of them out but I like writing less code so I have an example of how to do that as well. The only differences here is we are doing all the work internally to automatically expose this feature to the caller. You will notice though that we are not using the evaluate method here. We can simply call our getter by referring to this and using a dynamic name. component accessors="true" { property userid; property firstname; property lastname; /** * @hint this method will return an array of key/pair values for * each property in our component dynamically. */ public array function getPropertyValues(){ // the properties of our component var properties = getMetaData(this).properties; // the return array var propertyValues = []; for(i=1; i <= arrayLen(properties); i++){ var property = {}; property.key = properties[i].name; property.value = getPropertyValue(property.key); arrayAppend(propertyValues,property); } return propertyValues; } private any function getPropertyValue(String key){ var method = this["get#key#"]; return method(); } } This is an example of getting the values from the component above. <cfscript> user = new User(); user.setUserId(10); user.setFirstName("Dan"); user.setLastName("Vega"); writeDump(user.getPropertyValues()); </cfscript>

The weird thing is if you try and use the same method of calling the getter outside of the component it just does not work. <cfscript> user = new User(); user.setUserId(10); user.setFirstName("Dan"); user.setLastName("Vega"); properties = getMetaData(user).properties; for(i=1; i <= arrayLen(properties); i++){ property = properties[i]; method = user["get#property.name#"]; writeOutput( property.name & ":" & method() & "<br/>"); } </cfscript> The code above will not work, it just returns nothing for each.

With the new script upgrades in ColdFusion 9 I imagine people will be running into issues like this so I thought I would share this with you. If anyone knows why I can't use that same syntax outside of the component I would love to hear it. It's always better to understand why you can't do something instead of just accepting the fact that you can't!

This entry was posted on October 7, 2009 at 5:02 PM and has received 3563 views. Comments 6 | Print this entry.