ColdFusion ORM - Attaching calculated values to your entities

There will come a time when you need to add a calculated value to your entity. In this example we will look at why you would want to do this and how you can easily accomplish it. I whipped up a very simple user manager example. First we have some orm settings in our application component. The main thing to get out of this is that we are going to be using event handling. // orm settings this.ormenabled = "true"; this.datasource = "usermanager"; this.ormsettings = { dbcreate="update", logSQL=true, eventhandling=true, cfclocation="model" };

Our user entity is very basic and there is nothing special going on at this point. component persistent="true" table="Users" { property name="userid" type="numeric" ormtype="int" fieldtype="id" generator="increment"; property name="firstname" type="string" ormtype="string" ; property name="lastname" type="string" ormtype="string" ; property name="dob" type="date" ormtype="date" ; } Now what if we wanted to display the users age somewhere in our code? We could easily do something like this. dateDiff("yyyy",user.getDOB(),now()); What if we had more of a complex calculation though? This is not logic that you would want to have to add everywhere this value is needed. Luckily we can easily add a field to our entity without persisting it to the database. The first thing we do is add the property and set persistent to false. This tells our entity that when we save/update we are not storing this property. component persistent="true" table="Users" { property name="userid" type="numeric" ormtype="int" fieldtype="id" generator="increment"; property name="firstname" type="string" ormtype="string" ; property name="lastname" type="string" ormtype="string" ; property name="dob" type="date" ormtype="date" ; property name="age" type="numeric" persistent="false"; }

At this point your thinking that we could probably just write a setter that would calculate the age right? Short answer yes, long answer is no. If we take a closer look you will see why. component persistent="true" table="Users" { property name="userid" type="numeric" ormtype="int" fieldtype="id" generator="increment"; property name="firstname" type="string" ormtype="string" ; property name="lastname" type="string" ormtype="string" ; property name="dob" type="date" ormtype="date" ; property name="age" type="numeric" persistent="false"; public void function setAge(){ variables.age = dateDiff("yyyy",this.getDOB(),now()); } } If you were to use the user entity below and load a record the age property will be null. Your next thought would be to add it to the constructor right? Well, turns out this would not work either because your trying to set the age when we don't have date of birth loaded yet. public User function init(){ this.setAge(); } That is where event handling comes in. I have talked about event handling before so I am not going to get into how it works. Just know for this example if event handling is turned on we have many methods available for us to listen for. One of them is post load and it happens after an object has been loaded. This is a perfect time to calculate age because we have our date value now. component persistent="true" table="Users" { property name="userid" type="numeric" ormtype="int" fieldtype="id" generator="increment"; property name="firstname" type="string" ormtype="string" ; property name="lastname" type="string" ormtype="string" ; property name="dob" type="date" ormtype="date" ; property name="age" type="numeric" persistent="false"; public User function init(){ this.setAge(); } public void function setAge(){ variables.age = dateDiff("yyyy",this.getDOB(),now()); } public void function postLoad(){ this.setAge(); } } Finally there is one more check we need to run. What if the date of birth is null? If it is we are going to get an error when we try and calculate our age. We can run a quick check to make sure its not null. component persistent="true" table="Users" { property name="userid" type="numeric" ormtype="int" fieldtype="id" generator="increment"; property name="firstname" type="string" ormtype="string" ; property name="lastname" type="string" ormtype="string" ; property name="dob" type="date" ormtype="date" ; property name="age" type="numeric" persistent="false"; public void function setAge(){ variables.age = dateDiff("yyyy",this.getDOB(),now()); } public void function postLoad(){ if(!isNull(this.getDOB())){ this.setAge(); } } }