ART#215 - What are transient properties in ATG?

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Properties which are not associated with any tables are called transient properties.
Now, the question arises, why would we not want a property to be associated with a table? If our property is not associated with a table, how (or where) would we store data corresponding to this property?

Let us take an example: in "user" item-descriptor of ProfileAdapterRepository, there is a property called "registrationDate" of type Timestamp. This property, like any other property, is mapped to a table's column. Pretty much straightforward till now?

Now, consider a situation, when on the website's MyAccount section, you need to display the number of days/months/years, the user has been a part of your website.
Something like:

Ankit Jain, registered since 4 days, 4 months and 2 years. 

Now, you have two options,

OPTION#1: In the JSP (or a droplet), read the user's registrationDate property, and calculate the days, months, years and then display it.
Drawback: Workable, but the calculation logic goes into the droplet. Not much of a good coding standard.

OPTION#2: Transient Property. Let us see this in a moment.

How to we declare a property as transient?

Let us backtrack a little and remember the process of creating a normal property for an item-descriptor. For people who do not know this, can revisit the concept HERE. It goes something like this-

<item-descriptor name="user" .. some other stuff.. >
 <table name="TABLE_NAME" type="primary or auxiliary or whatever">
  <property name="registrationDate" column-name="SOME_COLUMN" />
 </table>
</item-descriptor>

Since a transient property is not mapped to any table, it is simple declared outside of a table tag. Let us assume, we are creating a new transient property "registeredSince" of the type string in user item-descriptor. The <property>tag is same, but the only difference is that, it is declared OUTSIDE of the <table> tag. Since there is no table for this property, there is no column-name attribute in this property. So, the XML goes something like:-

<item-descriptor name="user" .. some other stuff.. >
<property name="registeredSince" data-type="string" />
 <table name="TABLE_NAME" type="primary or auxiliary or whatever">
  <property name="registrationDate" column-name="SOME_COLUMN" />
 </table>
</item-descriptor>

Now, we have simply created a new transient property in existing item-descriptor.
This being done, the question arises, how do we make this property calculate and return the number of  (days/month/years), the user is registered since? The answer follows in the next article - How to add functionality to a transient property?

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