Objectives
After completing this lesson,you should be able to do the following
- Describe packages and list their components
- Create a package to group together related variables,cursors,constants,exceptions,procedures,and fuctions.
- Designate a package construct as either public or private
- Invoke a package construct
- Describe the use of a bodiless package
Lesson Agenda
- Identifying the benefits and the components of packages
- Working with packages
- -Creating the package specification and body
- -Invoking the package subprograms
- -Removing a package
- -Displaying the package information
What Are PL/SQL Packages?
- A package is a schema object that groups logically related PL/SQL types,variables,and subprograms.
- Packages usually have two parts:
- -A specification(spec)
- -A body
- The specification is the interface to the package.It declare the types,variables,constants,exceptions,cursors,and subprograms that can be referenced from outside the package.
- The body defines the queries for the cursors and the code for the subprograms.
- Enable the Oracle server to read multiple objects into memory at once.
Advantages of Using Packages
- Modularity:Encapsulating related constructs
- Easier maintenance:Keepling logically related functionality together
- Easier apllication design:Coding and compiling the specification and body separately
- Hiding information:
- Only the declarations in the package sepcification are visible and accessible to applications.
- Private constructs in the package body are hidden and inaccessible.
- All coding is hidden in the package body
- Added functionality:Persistency of public variables and cursors
- Better performance:
- -The entire package is loaded into memory when the package is first referenced.
- -The is only one copy in memory for all users
- -The dependency hierarchy is simplified.
- Overloading:Multiple subprograms of the same name
- The package is a powerful and important element of the PL/SQL language.It should be the cornerstone of any application development project.
- Always construct your application around packages;avoid standlone procedure and fuctions.Even if tody you think that only one procedure is needed for a certain area of functionality,in the future you will almost certainly have two,then three,and then a dozen.At which point,you will find yourself saying,"Gee,I should really collect those together in a package!" That`s fine,except that now you have to go back to all the invocations of those unpackaged procedures and functions and add in the package prefix.So start wit a package and save yourself the trouble.