There are a lot of blog posts already out there in the Coldfusion "blogosphere" here is my addition to the already great resources. I've decided to start this series of blog posts from the very first steps and go from there.
What is ORM?
ORM stands for Object-relational Mapping and basically is a method of creating a relationship between objects and a relational database. The "main" benefit of using ORM in is that it can substantially reduce the amount of code that a programmer needs to write. The mundane functions to Create, Read, Update and Delete (CRUD) elements in database tables is automatically handled by ORM as well as allowing the programmer to specify how objects relate to each other (one-to-many, one-to-one etc) that are then "translated" into sql queries when handling the objects.
Hibernate is most probably the most well known ORM library for the Java language and is what Coldfusion 9 uses for it's ORM framework. There are already a few ORM frameworks created specifically for the CFML language (Transfer, Reactor, etc) which have all be built using Coldfusion. Adobe has integrated Hibernate support into the Coldfusion engine.
Setting up your Application for Persistence
When you are creating an Application and you want to use Hibernate to persist your components (objects) you need to set up persistence in your Application.cfc component. A very simply Application.cfc would looks something like:
A Persistent Component
Keeping things very simple we will create a person component. In this first part the person will be very simple and we will make things a little more complicated later on.
<cfcomponent displayname="person" hint="I am a person object" output="false" persistent="true">
<cfproperty name="id" generator="native" fieldtype="id" >
<cfproperty name="dob" ormtype="date">
We now have a persistent component. Coldfusion automatically creates the setters and getters for our properties, additionally we can use a series of functions to perform the standard CRUD functions.
Using ORM on our Component
To Create and persist (update) the data of our component we use two functions:
- entityNew(): creates a new entity
- entitySave(): updates or inserts the data into the database for the specified entity.
To Read a person from the database we use the method entityLoad(). The entityLoad method can take a few different methods, in order to return ALL persons in our database we simply use entityLoad('person') to return an array of objects. To return a single person we use entityLoad('person',1,true) to return the person with the ID of 1, the true indicates to return the actual entity instead of an array of entities.
To Update an entity we use the entityUpdate() method.
To Delete an entity we first have to load the entity into a variable e.g.:
<cfset personToDelete= entityLoad('person',1,true)>
There we have the standard CRUD functions without having to write a single line of code, or a single query. We simply specified the correct properties and attributes in our Application.cfc and our component and we automatically have the functionality that we need.
Oh, one last rather useful function is the EntityToQuery() function, once you have called your entity load function you end up with an array of objects, queries are often easier to deal with so you can convert your array of objects into a query. For my person object I would do the following:
<cfset people = entityLoad('person')>
<cfset qryPeople = entityToQuery(people)>
We got a brief overview of what ORM is and what Hibernate is, we also created a very simple object that will be persisted in a database with the datasource name of "test". Notice we never bothered mentioning what DB it was we don't care either. Next we will expand our person object by adding a one-to-many relationship and seeing how we manipulate the related objects.Happy Coding...
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