VO (View Object)

VO Represent a query result.
VO's are used for joining, filtering, projecting, and sorting your business data.
VO Can be based on any number of entity objects.
VO Can also be constructed from a SQL statement.

We have four types of View Objects and they are:

1) Manual VO
2) Automatic VO
3) Validation VO
4) Property VO

Manual VO: If we are writing our own SQL query then it will be called as Manual VO.

Automatic VO: Automatic VO is when we select an Entity Object automatically it will select the Query.

Difference between Manual and Automatic VO is:

• If we want to perform DML operations then we can go for VO that should be based on Entity Object.

• We go for Manual VO if we are using simple SELECT statement.

NOTE: Note that when we create VO (View Object) all the table columns will be converted into attributes, hence here we call columns as attributes.

Validation VO: Validating the data in the Data Base, example using WHERE condition in the SELECT statement.

Property VO: Attributes / columns without Data Base columns comes under property VO. These attributes are also called as Transient attributes.

Example: Suppose there is a table which holds student marks so therefore it contains 6 columns to hold six subject marks for each student. 

There is no total column in the table to store the total marks of the student separately. 

Now in the output for display purpose we are taking TOTAL attribute, hence which is not from Data Base table and this TOTAL attribute is called Transient attribute.