Beans, methods, access and change? What is the recommened practice for handling them (i.e. in ColdFusion)?

Question

I am new to programming (6 weeks now). i am reading a lot of books, sites and blogs right now and i learn something new every day.

Right now i am using coldfusion (job). I have read many of the oop and cf related articles on the web and i am planning to get into mxunit next and after that to look at some frameworks.

One thing bothers me and i am not able to find a satisfactory answer. Beans are sometimes described as DataTransferObjects, they hold Data from one or many sources.

What is the recommended practice to handle this data?

Should i use a separate Object that reads the data, mutates it and than writes it back to the bean, so that the bean is just a storage for data (accessible through getters) or should i implement the methods to manipulate the data in the bean.

I see two options.
1. The bean is only storage, other objects have to do something with its data.
2. The bean is storage and logic, other objects tell it to do something with its data.

The second option seems to me to adhere more to encapsulation while the first seems to be the way that beans are used.

I am sure both options fit someones need and are recommended in a specific context but what is recommended in general, especially when someone does not know enough about the greater application picture and is a beginner?

Example:
I have created a bean that holds an Item from a database with the item id, a name, and an 1d-array. Every array element is a struct that holds a user with its id, its name and its amount of the item. Through a getter i output the data in a table in which i can also change the amount for each user or check a user for deletion from this item.

Where do i put the logic to handle the application users input?
Do i tell the bean to change its array according to the user input?
Or do i create an object that changes the array and writes that new array into the bean?

(All database access (CreateReadUpdateDelete) is handled through a DataAccessObject that gets the bean as an argument. The DAO also contains a gateway method to read more than one record from the database. I use this method to get a table of items, which i can click to create the bean and its data.)

Answer 1

You're observing something known as "anemic domain model". Yes, it's very common, and no, it's not good OO design. Generally, logic should be with the data it operates on.

However, there's also the matter of separation of concerns - you don't want to stuff everything into the domain model. For example, database access is often considered a technically separate layer and not something the domain models themselves should be doing - it seems you already have that separated. What exactly should and should not be part of the domain model depends on the concrete case - good design can't really be expressed in absolute rules.

Another concern is models that get transferred over the network, e.g. between an app server and a web frontend. You want these to contain only the data itself to reduce badnwidth usage and latency. But that doesn't mean they can't contain logic, since methods are not part of the serialized objects. Derived fields and caches are - but they can usually be marked as transient in some way so that they are not transferred.

Answer 2

Your bean should contain both your data and logic.

Data Transfer Objects are used to transfer objects over the network, such as from ColdFusion to a Flex application in the browser. DTOs only contain relevant fields of an object's data.

Where possible you should try to minimise exposing the internal implementation of your bean, (such as the array of user structs) to other objects. To change the array you should just call mutator functions directly on your bean, such as yourBean.addUser(user) which appends the user struct to the internal array.

No need to create a separate DAO with a composed Gateway object for your data access. Just put all of your database access methods (CRUD plus table queries) into a single Gateway object.