Tuesday, June 29, 2010



Tables and structures can be expanded in one of two different ways:

Append structures allow you to enhance tables by adding fields to them that are not part of the standard. With append structures; customers can add their own fields to any table or structure they want.

Append structures are created for use with a specific table. However, a table can have multiple append structures assigned to it.

If it is known in advance that one of the tables or structures delivered by SAP needs to have customer-specific fields added to it, the SAP application developer includes these fields in the table using a Customizing include statement.

The same Customizing include can be used in multiple tables or structures. This ensures consistency in these tables and structures whenever the include is extended.

Nonexistent Customizing includes do not lead to errors.

Append structures allow you to attach fields to a table without actually having to modify the table itself.

Append structures may only be assigned to a single table. A table may, however, have several append structures attached to it. Whenever a table is activated, the system searches for all active append structures for that table and attach them to the table. If an append structure is created or changed and then activated, the table it is assigned to is also activated, and all of the changes made to the append structure take effect in the table as well.

You can use the fields in append structures in ABAP programs just as you would any other field in the table.

Note: If you copy a table that has an append structure attached to it, the fields in the append structure become normal fields in the target table.

You create append structures in the customer namespace. This protects them from being overwritten at upgrade or during release upgrade. New versions of standard tables are loaded during upgrades.

The fields contained in active append structures are then appended to the new standard tables when these new standard tables are activated for the first time.

From Release 3.0, the field sequence in the ABAP Dictionary can differ from the field sequence in the database. Therefore, no conversion of the database table is necessary when adding an append structure or inserting fields into an existing one. All necessary structure adjustment is taken care of automatically when you adjust the database catalog (ALTER TABLE). The table's definition is changed when it is activated in the ABAP Dictionary and the new field is appended to the database table.

Pay attention to the following points when using append structures:
You cannot create append structures for pool and cluster tables.
If a table contains a long field (either of data type LCHR or LRAW), then it is not possible to expand the table with an append structure. This is because long fields of this kind must always be the last field in their respective tables. No fields from an append structure may be added after them.

If you use an append structure to expand an SAP table, the field names in your append structure must be in the customer namespace, that is, they must begin with either YY or ZZ. This prevents naming conflicts from occurring with any new fields that SAP may insert in the future.

Some of the tables and structures delivered with the R/3 standard contain special include statements:

Customizing includes. These are often inserted in those standard tables that need to have customer specific fields added to them.

In contrast to append structures, Customizing includes can be inserted into more than one table. This provides for data consistency throughout the tables and structures affected whenever the include is altered.

Customizing include programs is part of the customer namespace: all of their names begin with 'CI_'. This naming convention guarantees that nonexistent Customizing includes do not lead to errors. No code for Customizing includes is delivered with the R/3 standard.

You create Customizing includes using special Customizing transactions. Some are already part of SAP enhancements and can be created by using project management (see the unit on 'Enhancements using Customer Exits').

The Customizing include field names must lie in the customer namespace just like field names in append structures. These names must all begin with either 'YY' or 'ZZ'.

When adding the fields of a Customizing include to your database, adhere to same rules you would with append structures.

Every time they define a data element, the SAP application programmers define keywords in different lengths and a short description for each data element.

You create field exits in Project management. Field exits are processed when the user leaves a screen that contains a field which refers to a data element containing a field exit.

SAP lets you create a field exit for every input-ready screen field that has been created with reference to the ABAP Dictionary. The additional program logic is stored in a function module and is executed at a specific point in the PAI logic.

The slide shows the order in which processing takes place. Before the PAI logic of the screen is executed, the system performs the following checks: First the system checks if all the required fields have been filled in. If a required field is empty, the screen is shown again.

The system then checks that data has been entered in the correct format.

Any defined field exits are executed next. For example, by sending an error message you can have the screen sent again.

Once all the field exits have been checked, the screen is processed as normal.

Field transport
Foreign key check
Processing the PAI module

Field exits take you from a screen field with a data element reference to a function module. Field exits can be either global or local:

Global field exits are not limited to a particular screen: If a global exit's data element is used on several screens, the system goes to the function module for all these screens after activating the field exit. Here you can, for example, edit the contents, force a new entry to be made by outputting an error message, or prohibit certain users from proceeding further.

Local field exits are valid for one screen only. If you assign a screen from a specific program to a field exit, then the system will go to the appropriate function module from this screen once the exit has been activated.

You can either create a global field exit or up to 36 local field exits for a data element, but not both.

Each exit number refers to a different function module. Field exit function modules adhere to the following naming convention:

Suffix (for local field exit): _0 to _9, _A to _Z
To create field exits; choose Utilities in the ABAP Workbench. Choose Enhancements and then Project management to edit field exits and to implement customer exits. Do not create field exits directly from the Function Builder.

Choose Goto -> Global enhancements -> Field exits to start the transaction for maintaining field exits. To create a new enhancement, use the menu path Text Enhancements -> Create.

Enter the name of the data element to which your screen field refers in the modal dialog box. The Function Builder is started with a special naming convention and interface options. The system specifies the name of the field exit. Do not change this name. Create the function module in a customer function group.

The function module must be assigned to an existing customer function group.

The function module interface is fixed and cannot be changed. The function module has an import parameter INPUT and export parameter OUTPUT. The contents of the screen field are stored in parameter INPUT. The contents of OUTPUT are returned in the screen field when you leave the function module.

Field exits are not transported automatically. Therefore, you must assign the value of INPUT to OUTPUT in your source code. Otherwise the screen field would be blank after executing the field exit.
The following ABAP statements are not allowed in field exit function modules:

When you debug a screen that is referenced by a field exit, the field exit code is ignored by the debugger. As with any normal function module, you can, however, debug the field exit code in the Function Builder's test environment.

You can create local field exits that relate to a specific screen. A global field exit must already exist.
Edit the local field exit based on the global field exit.

You can create up to 36 local field exits, each of which carries a unique suffix. The system proposes a name for the function module; you should use this name.

Defining local field exits means that the function module of the global field exits initially created is no longer used. However, you must not delete it, for technical reasons. The field exits in the system would be deleted if you deleted the global function module of the field exit from the list.

You must activate the field exit as well as the function module. Also note that field exits are only taken into account during screen execution if the R/3 profile parameter abap/field exit = YES has been set for all application servers. (This profile parameter is set to 'NO' by default).

If you declare field exits for multiple screen fields, you have no control over the order in which they are processed. In particular, you cannot access the contents of other screen fields in a field exit.

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