Tài liệu Pro Oracle Application Express P2 docx

For example, the following code catches the exception and sets the value of an application item: declare v_salary INTEGER; begin select salary into v_salary from emp where empno

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Report Pagination Style

Different report pagination styles will affect the performance in displaying the report For example, some of the pagination styles will display something like “Row Ranges X to Y of Z,”

If you do not need to display how many total rows are returned from the query, you should choose to use a pagination style that displays only “Row Ranges X to Y.”

Error and Exception Handling

Your APEX application can use many different anonymous PL/SQL blocks, functions, proce-dures, and packages when it is executing If an error or exception occurs during the execution

of some code, you need to be able to handle that error or exception gracefully, in such a fashion that flow of execution by the APEX engine is not broken For example, the following code catches the exception and sets the value of an application item:

declare

v_salary INTEGER;

begin

select

salary

into

v_salary

from

emp

where

empno = :P1_EMPNO;

return v_salary;

:APP_ERROR_MSG := null;

exception

when no_data_found then

:APP_ERROR_MSG := 'Could not find the employee record.';

end;

You can then display the application item on the page in an HTML region using this syntax:

&APP_ERROR_MSG

You would then create a branch on the page to branch back to itself if the value of the application item is not null, thereby enabling the user to see the error and correct it

Packaged Code

APEX allows you to write SQL and PL/SQL code directly in a number of places via the Applica-tion Builder interface For example, suppose you create the following after-submit process in your login page to audit that a user logged in to the application

C H A P T E R 1 ■ D E V E L O P M E N T B E S T P R A C T I C E S 23

begin

insert into tbl_audit

(id, user_name, action)

values

(seq_audit.nextval, :APP_USER, 'Logged On');

end;

Now, while this would work, it also means that if you ever want to modify the logic of the

auditing, you need to change the application For example, notice that you aren’t currently

storing a timestamp of when the audit action was performed To add that functionality, you

would need to modify the tbl_audit table and add an extra column to store the timestamp

information (if that column did not already exist), and then edit the application to change the

PL/SQL page process to include the timestamp information, like this:

begin

insert into tbl_audit

(id, ts, user_name, action)

values

(seq_audit.nextval, sysdate, :APP_USER, 'Logged On');

end;

So, potentially for a very simple change, you might need to modify the application in

development, export a new version of the application, import that version into a test

environ-ment, and so on through to production

A much more efficient way is to try to isolate the number of places you directly code logic

into your application by placing that code into a package, and then calling the packaged

pro-cedure or function from your application For example, you could change the PL/SQL page

process to simply do this:

begin

pkg_audit.audit_action('Logged On');

end;

This allows you to encapsulate all of the logic in the packaged code Assuming you are not

making fundamental changes to the package signature, you can modify the internal logic

with-out needing to change the application This design would allow you to change the table that the

audit information is stored in or to add new columns and reference session state items without

needing to change anything in the application itself All you would need to do is recompile the

new package body in the development, test, or production environment This would result in

much less downtime for the application, since you no longer must remove the old version of

the application and import the new version Using this method really does allow downtimes of

just a few seconds (the time it takes to recompile the package body), as opposed to minutes, or

potentially hours, while new versions of the applications are migrated

Obviously, you won’t always be able to completely encapsulate your logic in packages

And sometimes, even if you do encapsulate the logic, you may need to change something in the

application (for example, to pass a new parameter to the packaged code) However, it is good

practice to use packaged logic where you can Using packaged code can save you a lot of time

later on, as well as encourage you to reuse code, rather than potentially duplicating code in a

number of places throughout your application

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Summary

This chapter covered some best practices for using APEX You don’t need to follow our advice Many people just charge in and begin coding without thinking to lay a solid foundation for their work Some of what we advocate in this chapter may actually slow you down at first, but

it will save you time in the long run Helping you to work more efficiently, and taking a long-term view of doing that, is one of the reasons we’ve written this book

■ ■ ■

C H A P T E R 2

Migrating to APEX from Desktop

Systems

Many organizations come to rely on systems that have been built using desktop applications

such as Microsoft Excel, Access, and similar tools For example, employees might store their

own timekeeping data in an Excel spreadsheet, which is sent to the payroll department each

month, or the sales department might keep all its customer details in an Access database

These applications often begin as simple data-entry systems, but evolve over time as more

functionality is added or the business rules regarding the data change Using desktop-based

systems to manage data has a number of drawbacks, such as the following:

• Each person who wants to work with the data needs to install the client software (for

example, Excel) on his machine

• Data cannot be easily shared with other applications

• In the case of Excel, only one person can be in control of the data at once

• It is difficult to manage the changes made by people working with their own copy of the

data

• The data might not be backed up as part of any regular backup procedures

• It can be difficult to establish and restrict exactly who has access to the data

• There is no fine-grained control over what data a user is allowed to view and modify

• Confidential data can be taken off-site by a user, via an e-mail attachment or by copying

a spreadsheet onto a USB key, for example

By using APEX, you can avoid many of these issues Users won’t need to install any

dedi-cated client software, because all they will need to use your APEX application is a supported

browser You can store the data centrally within the Oracle database, which enables it to be

backed up as part of your regular database backup policy (for example, if you perform database

backups using RMAN, the application data will also be backed up)

You can also use features such as Fine-Grained Access Control (FGAC) to control the data

users are allowed to access When you combine this with auditing, you will not only be able to

control exactly what data users can access, but you will also have an audit trail of what data

they did access

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We want to stress that APEX is capable of far more than just being an Excel or Access replacement You really are limited only by your imagination in the applications that you can create However, many existing Excel and Access systems could benefit from being replaced by APEX applications, so it can be a great place to begin learning how to take advantage of this powerful and rapid development tool

Excel Migration

In this section, we will demonstrate how you can take an existing Excel spreadsheet and convert it into an APEX application The sample spreadsheet, shown in Figure 2-1, is used

to document the status of bugs that have been reported in another application Each bug is assigned to a developer, and the status of the bug is changed from open to closed when that bug has been fixed

Figure 2-1. Bug report spreadsheet

The existing spreadsheet solution suffers from many of the drawbacks mentioned at the beginning of this chapter, particularly the fact that only one person at a time can be in control

of changing the spreadsheet Typically in this sort of scenario, one person is tasked with main-taining the spreadsheet, and might receive the bug reports from the testing team via e-mail When a bug report e-mail message is received, the person in charge of maintaining the spread-sheet adds the bug to the list and looks for a developer to assign the bug to, usually based on who has the least number of open bugs (which is far from an ideal way to measure how busy the developers are!) The spreadsheet maintainer might send weekly or monthly updates to let people know the status of the bugs at that point in time

Clearly, this sort of system could be improved by removing the potential bottleneck of the spreadsheet maintainer needing to collate all of the data If the testing team members were allowed to enter new bugs directly into the system themselves, the bugs would appear in the report immediately Also, if the developers could select which bugs to work on, rather than having bugs assigned to them, they would likely pick ones related to the areas of the system they know well

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Creating a New Application Based on a Spreadsheet

One of the quickest and easiest ways to migrate your existing spreadsheet to an APEX

applica-tion is to use the Create Applicaapplica-tion wizard to base the applicaapplica-tion on an Excel spreadsheet, as

shown in Figure 2-2

Figure 2-2. Creating an application from a spreadsheet

When you use the wizard to create an application based on a spreadsheet, the wizard will

create a lot of functionality to manage the data automatically for you The application will

con-tain methods for querying, inserting, deleting, and modifying the data, without you having to

write a single line of code

Importing the Data

You are given two options for importing the data from the spreadsheet:

Copy and paste the data: If you have a relatively small amount of data, you can choose the

copy-and-paste method, which will allow you to paste up to 30KB of data

Upload the data as a file: If your spreadsheet contains more data than the 30KB

copy-and-paste method allows, you will need to upload the data as a comma-separated value (CSV)

or tab-delimited file instead

In this example, we will use the file-upload method You can use the Save As option in

Excel to save the data in CSV or tab-delimited files You will need to do this for the data on each

worksheet individually Make sure you give each worksheet file a unique name; otherwise, you

will overwrite your previous file

Once you have saved your data in a suitable format, you can select that file in the Create

Application wizard and specify some options that will be used when the wizard parses the file,

as shown in Figure 2-3

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Figure 2-3. Uploading a CSV file

The following are some of the options that can be specified:

Separator: By default, the separator is set to a comma If you have a tab-delimited file,

you can specify \t (a backslash followed by a lowercase T) You can actually specify any

separator here, such as a colon, but generally it’s best to stick to the well-known CSV or tab-delimited format, unless you have no control over the source data

Optionally Enclosed By: You can use this setting to specify a character that marks the start

and end of a particular column of data This can be useful if you are using a CSV file and some of your data values include commas (for example, addresses might have commas) You can enclose the data values with quotation marks, which would prevent the embed-ded commas from being interpreted as the start of a new column

First row contains column names: Check this option if the first row of the imported data

includes text that you want to use as the column names

File Character Set: This is the character set encoding of the file that you are uploading.

■ Caution Excel does not export CSV or tab-delimited data in UTF-8 by default There is the possibility for data corruption if you export from Excel using either of those formats and subsequently load that data into a UTF-8 database If your database uses UTF-8, make sure to export from Excel in UTF-8

The Globalization settings are not displayed by default, and it is quite easy to miss them Clicking the Globalization heading expands the page, making these options visible These options allow you to define the currency symbol, group separator, and decimal character For example, if your spreadsheet data contains prices that include a currency symbol (such as the euro or yen symbol), you will need to specify that symbol; otherwise, the wizard will not cor-rectly identify that column as a numeric field

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Setting Table Properties

The next page of the Create Application wizard, shown in Figure 2-4, lets you set the table

properties for the data that will be imported Here, you can select the schema and table name,

and rename columns There is a Preserve Case option, but we don’t recommend enabling it,

since it can be the cause of many problems when people try to perform a query against your

table and don’t use the same case for the column names that you have specified here

Figure 2-4. Setting the table properties during the import

The wizard generally does a good job of working out the data type that should be used for

each column, based on the data in that column However, you can modify the data type,

for-mat, or column length of any of the columns You can also choose whether or not to upload

individual columns, which can be very useful when you want to import only certain columns

from the original data file For this example, the only change we made on this page was to set

the table name to BUGLIST

Selecting Settings for Forms, Reports, and Charts

After clicking the Next button, you are taken to a page that lets you set the singular and plural

names for the items of the data These plural and singular names are used in forms and reports

that you develop later We used “Bug” as the singular and “Bugs” as the plural You can also

change the text that will be used for labels for each of the columns We changed the BugId

col-umn label to read Bug Id

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The next page in the wizard lets you select columns on which to base reports and charts It can sometimes be a bit confusing at this point to pick exactly which columns you want to use, but you can always modify the reports and charts later We selected the REPORTED, STATUS, REPORTED_BY, and ASSIGNED_TO columns, as shown in Figure 2-5

Figure 2-5. Choosing the summary columns for reports and charts

On the next page of the wizard, you can select any columns whose values you wish to have aggregated (for example, calculating the sum or average) in a report Since that sort of report doesn’t make sense in the context of this example, we did not select any columns on this page The next few pages of the wizard let you specify the name of the application and give you the option of using a pie chart or vertical bar chart

Selecting the Theme

The final page in the wizard lets you select the theme to be used for the application In APEX version 2.2, you can select from 18 built-in themes (you can also create your own themes) We selected the Light Blue theme (theme 15)

After you have selected a theme, the wizard will create the application, and you will then

be taken to a page where you can choose to run or edit the application

Running the New Application

If you run the application you just created, you will be presented with a page asking for your username and password This is because the application was created using APEX authentica-tion This authentication method means that you will need to log in using the credentials of an APEX user that has been created by a workspace administrator Figure 2-6 shows the page that

is displayed once you have logged in to the application

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Figure 2-6. Home page of the application based on the spreadsheet

Using the Developer Toolbar

Because we ran the application from within the Application Builder environment, you can

see the Developer toolbar displayed at the bottom of the screen This toolbar gives you quick

access to certain actions You can edit the application, edit the current page, create new

elements on the current page, and view the current session information You can use Show

Edit Links to place a link next to each element on the page that, when clicked, will give you a

pop-up page that lets you edit the properties of that particular page element directly

The Debug option on the toolbar is a great feature It will run the page and include

detailed debugging information, showing precisely what the APEX engine is doing, along

with detailed timing information, allowing you to identify exactly how much time each

ele-ment of the page is taking to process Figure 2-7 shows a small section from the home page

with debugging enabled

The timing information displayed when you run the page in debug mode is cumulative

For example, in Figure 2-7, you can see that before the report is displayed, the timing shows

0.20 second; after the report is displayed, the timing shows 0.37 second Therefore, you can

conclude that the report took 0.17 second to process (0.37 – 0.20) Using debug mode can be

a very quick and easy way to home in on any performance problems in your application

When you have finished looking at the page in debug mode, simply click the No Debug

option, and the page will be displayed without any debug information