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Structures

Structures are data objects (comprised of components of any data type) that are saved in sequence in the memory. The data type of a structure is a structured type or a structure defined in the ABAP Dictionary.

In a program, a structured type or structure is created using the additions BEGIN OF ... END OF additions of the statements TYPES, DATA etc. They can also be created dynamically using RTTC methods. Im ABAP Dictionary, structures appear as standalone data types, as types of database tables, of classic views or of CDS entities.

Programming Guidelines

Types of Structures

Structures are named as follows (depending on the type of the component):

A structure that contains static or dynamic components is (formally) a static or dynamic data object, respectively.

The following figure illustrates a deep structure.

Mapping

Note

The term "nested structure" must not be confused with the term "deep structure". A nested structure is flat if it only contains flat components and subcomponents. A nested structure is deep when it has at least one deep component or subcomponent.

Example

Nested structure. The substructure is created using a reference to the dictionary structure SCARR for the second component. Access to the components using the structure component selector (-).

DATA:
  BEGIN OF struct,
    name  TYPE c LENGTH 10 VALUE 'SCARR',
    scarr TYPE scarr,
  END OF struct.

SELECT SINGLE *
       FROM scarr
       WHERE  carrid = 'LH'
       INTO CORRESPONDING FIELDS OF @struct-scarr.

cl_demo_output=>new(
)->write_data( struct-name
)->write_data( struct-scarr-carrid
)->write_data( struct-scarr-carrname
)->display( ).

Example

Deep structure The following structure contains deep components only.

DATA:
  BEGIN OF struct,
    text TYPE string,
    hex  TYPE xstring,
    tab  TYPE STANDARD TABLE OF i WITH EMPTY KEY,
    dref TYPE REF TO i,
    iref TYPE REF TO if_demo_output,
  END OF struct.

Using Structures

Structures are addressed either fully or by component, at appropriate operand positions. The structure component selector (-) is used for the latter case. In the case of data reference variables that are typed as a structure, the components of the structure to which the data reference variable points are addressed using the object component selector (->).

Special conversion and comparison rules apply to assignments that involve structures. Flat character-like structures differ in that they can be used like character-like data objects in many operand positions and included in the generic ABAP type clike. They can be specified in almost all operand positions where elementary character-like data objects are possible. The ABAP runtime environment then interprets the structure as an elementary field of the type c in the length of the structure. An exception to this are operand positions of string expressions and string functions.

For the assignement of structure components, there is a special statement MOVE-CORRESPONDING, a constructor operator CORRESPONDING, and a system class CL_ABAP_CORRESPONDING. The INTO clause of Open SQL also has an addition CORRESPONDING. The ASSIGN statement has a special variant COMPONENT OF STRUCTURE for dynamic access to stucture components.

Example

Inline-Deklaration einer Struktur wa in einer SELECT-Anweisung mit Bezug auf die Datenbanktabelle SCARR im ABAP Dictionary. Zugriff auf die Komponenten der Struktur über den Strukturkomponenten-Selektor (-). .

SELECT carrid, carrname
       FROM scarr
       INTO @DATA(wa).
  cl_demo_output=>write( |{ wa-carrid WIDTH = 5
                         }{ wa-carrname }| ).
ENDSELECT.
cl_demo_output=>display( ).

Example

Erzeugung einer Struktur als anonymes Datenobjekt mit dem Typ der Datenbanktabelle SCARR im ABAP Dictionary, auf das die Datenreferenzvariable dref zeigt. Verwendung über den Dereferenzierungsoperator (->*) als Zielbereich einer SELECT-Anweisung. Zugriff auf die Komponenten der Struktur über den Objektkomponenten-Selektor (->).

DATA(dref) = NEW scarr( ).

SELECT *
       FROM scarr
       INTO @dref->*.
  cl_demo_output=>write( |{ dref->carrid WIDTH = 5
                         }{ dref->carrname }| ).
ENDSELECT.
cl_demo_output=>display( ).

Example

Das folgende Beispiel zeigt, dass sich eine flache Struktur mit rein zeichenartigen Komponenten sowohl wie eine Struktur als auch wie ein zeichenartiges Datenobjekt verhalten kann.

DATA:
  BEGIN OF struct,
    col1 TYPE c LENGTH 5 VALUE '12345',
    col2 TYPE c LENGTH 5 VALUE 'abcde',
  END OF struct.

cl_demo_output=>new(
  )->write_data( struct
  )->write_data( struct-col1
  )->write_data( struct-col2
  )->write_data( CONV string( struct )
  )->display( ).

Using Deep Structures

The data content of deep structures is not saved in full within the memory bounds of the structure and the deep components are instead just references to the actual data. This means that some general restrictions apply when using deep structures (unlike flat structures):

Note

These restrictions are particularly important if single components in existing flat character-like structures are converted to strings, which makes the entire structure deep.

Example

The following two deep structures are not compatible and cannot be converted to each other.

DATA:
  BEGIN OF struct1,
    col1 TYPE c LENGTH 4,
    col2 TYPE REF TO data,
  END OF struct1,
  BEGIN OF struct2,
    col1a TYPE c LENGTH 2,
    col1b TYPE c LENGTH 2,
    col2 TYPE REF TO data,
  END OF struct2.

struct1 = struct2. "syntax error

Using Deep ABAP Dictionary Structures

The same restrictions apply to deep structures defined in ABAP Dictionary as to deep structures defined in ABAP programs. Further restrictions apply only when the following language elements forbidden in classes are used (only flat ABAP Dictionary structures can be specified in classes):

Boxed Components

The substructures of nested structures and structured components of classes or interfaces can be declared as boxed components.



Continue
Boxed Components
Examples of structures