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Extending Tables Without Modification Using Append Structures

Description

Customer fields can be added to structures and transparent tables without modifying the table itself, the new fields being entered in a separate append structure.

An append structure is a structure which is allocated to only one table. However, a single table can have several append structures. If an append structure is created or changed, the table to which it is assigned will be activated when the structure itself is activated and the changes will take effect there, that is, the fields of the append structure are appended to the allocated table. If a table is activated, on the other hand, all active append structures for the table will be appended to it.

Append structures are created by the customer in the customer name range and are thus protected against overwriting at the time of an upgrade or Release upgrade. During a Release upgrade, the new versions of the standard tables are imported and the fields contained in append structures are automatically reappended during activation.

Example: An append structure ZT is defined for table T.

            ----------------           -----------

            | K | F1 | F2 |        <-- | Z1 | Z2 |

            ----------------           -----------

           Dictionary table T          Append structure ZT for T

After activation, the runtime object belonging to T and the underlying database table have the fields from ZT, and '.append ZT' is displayed as the last line in the field display in the ABAP/4 Dictionary.

                   --------------------------

                   | K | F1 | F2 | Z1 | Z2 |

                   --------------------------

               Database table T, runtime object T

If you want to append fields to transparent tables or structures, create an append structure and insert the fields there. If you make further additions, extend this append structure. Therefore, create only one APPEND structure for each table/structure. This cannot then be deleted!

To create or change an append structure, go into the display of the table to be extended and choose Goto -> Append structures.

Notes:

• Customizing Includes and append structures
  If the table to be extended contains a Customizing Include, first check whether you can use this.

• Temporary workarounds
  If a field which is to be delivered with the standard R/3 System in the next release is to be temporarily inserted in the customer system, this should be done as a repair in the table itself and not in an APPEND structure. Otherwise, the field would occur twice when the Release is upgraded and would cause an error during activation.

• APPEND structures for special tables
  APPEND structures cannot be created for pooled and cluster tables, since this would require conversions. If you want to extend such tables, start by converting them to transparent tables. To do this, set the attribute 'transparent' in the technical settings of the table and then convert the table using the database utility. The table then also remains transparent during the Release upgrade.

• Long fields (VARC, LCHR, LRAW)
  If the table to be extended contains a "long" field, that is, a field with data type VARC, LCHR or LRAW, in the table to be extended, an extension with append structures is not possible since long fields must always be contained at the end of tables. In contrast, if a structure is to be extended with long fields, an append structure can be used.

• Indexes
  Indexes for the added fields must be defined in the original table. As indexes are now transport objects in their own right, there is no conflict with the R/3 standard and adjustment is not necessary at the time of a Release upgrade.

• Foreign keys
  Foreign keys for the appended fields are defined within the append structure. Fields of the allocated table can also be entered for the allocation of key field to foreign key field.

• Extending several tables with the same fields
  In this case, you can define a structure with these fields and include it as a substructure in all the append structures involved.

• Append structures in ABAP/4 programs
  You can use an append structure in programs in the same way as any other structure, for example, to transport fields from the allocated table into the append structure and the reverse (MOVE-CORRESPONDING).

• Difference to substructures
  To copy the fields of a substructure, a table must be extended by one line '.include ..'. Thus, the reference is based on the table. It is the other way round for append structures; the append structure has a reference to the appending table which itself remains unchanged. As a result, fields can be appended without modifying the table.

Further notes

Append structures are not delivered in the standard R/3 System. The append structure functionality is used to extend the standard system by specific fields in industry solutions and country-specific versions. However, you can create your own append structures for your own additions.

During the Release upgrade from 2.x to 3.0, the fields created by the customer are rolled out into an append structure, where possible, during Dictionary adjustment of transparent tables and structures. Adjustment is then not required in future Release upgrades.

Since the field sequence in the ABAP/4 Dictionary can be different to the Field sequence in the database, adding append structures or inserting fields into such append structures does not lead to the conversion of transparent tables.