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Logical Databases - Call by Function Module

Other versions: 7.31 | 7.40 | 7.54

How the Call Works

Logical databases can be called from any ABAP program using the function module LDB_PROCESS. Multiple logical databases can be called at the same time and a single logical database can be called more than once in the same executable program.

When a logical database is called using the function module LDB_PROCESS, the selection screen of the logical database is not displayed and is filled using interface parameters of the function module instead. The logical database does not trigger any GET events and passes the extracted data to callback routines during the call instead. This means that logical database calls using LDB_PROCESS disconnect the collection of data from the processing of the selection screens and the subsequent data preparation.

The logical databases do not need to be modified to do this, however the following restrictions apply:

  • If logical databases are not modified, the function module does not permit the same logical database to be called more than once in a row.
  • The subroutine pai is not called, which means that checks on selection criteria and parameters programmed in the routine are not executed.

These restrictions can be bypassed by inserting the subroutines ldb_process_init and ldb_process_check_selections in the database program.

Runtime Behavior

When called using the function module LDB_PROCESS, the subroutines of the logical database are called in the following order:

  • ldb_process_init
  • init
  • ldb_process_check_selections
  • put_node

    • None of the subroutines used for selection screen processing when associated with executable programs are called and the runtime environment does not trigger any reporting events in the calling program. Instead, the PUT statements of the logical database trigger actions in the function module that produce callback routine calls in the caller program.

    Interface Parameter of LDB_PROCESS

    Import parameters

    • LDBNAME
      Name of the logical database called.

    • VARIANT
      Name of a selection screen variant used to fill the selection screen of the logical database. The variant must be assigned to the database program of the logical database. The data is passed in the same way as when using the addition WITH SELECTION-TABLE in a program call using SUBMIT.

    • EXPRESSIONS
      In this parameter, additional selections can be passed in the table parameter SELECTIONS for the nodes of the logical database implemented in the selection include for dynamic selections. The data type of the parameter RSDS_TEXPR is defined in the type group RSDS. The data is passed in the same way as when using the addition WITH FREE SELECTIONS in a program call using SUBMIT.

    • FIELD_SELECTION
      In this parameter, a list of the required fields can be passed for the nodes of the logical database implemented in the selection include for free field selections. The data type of the parameter is the deep internal table RSFS_FIELDS from the type group RSFS. The component TABLENAME contains the name of the node and the deep component FIELDS contains the names of the fields being read.

    Table Parameters

    • CALLBACK
      The names of nodes and events are assigned to callback routines in this parameter. The parameter determines the nodes from which the logical database reads data (and when) and to which callback routines it passes this data (see below).

    • SELECTIONS
      Input values for the selection criteria and parameters of the selection screen of the logical database can be passed in this parameter. The data type of the parameter matches the structure RSPARAMS in ABAP Dictionary. The data is passed in the same way as when using the addition WITH SELECTION-TABLE in a program call using SUBMIT.

    If multiple selections are passed at the same time using multiple parameters, values passed in SELECTIONS and EXPRESSIONS overwrite the values in VARIANT.

    Read Depth and Callback Routines

    If a logical database is associated with a logical database, the GET statements determine the read depth of the logical database. If the function module LDB_PROCESS is used for calls, the read depth is determined by the node name passed to the parameter CALLBACK. A callback routine can be executed at two points in time for each node that requests data. These times match GET and GET LATE in executable programs. For each node, the name of the associated callback routine and the required times are specified in the table parameter CALLBACK. A callback routine is a subroutine in the caller program or in another program.

    For the event GET, the callback routine is called directly after the data of the node is read and before the processing of the lower subtree. For the event GET LATE, the callback routine is called after the lower subtree is processed.

    The row type of the table parameter CALLBACK is the flat structure LDBCB from ABAP Dictionary, with the following components:

    • LDBNODE
      Name of the node being read from the logical database.
    • GET
      Flag (values "X" or " ") for calling the associated callback routine for the event GET.
    • GET_LATE
      Flag (values "X" or " ") for calling the associated callback routine for the event GET LATE.
    • CB_PROG
      Name of the ABAP program in which the callback routine is defined.
    • CB_FORM
      Name of the callback routine.

    When an internal table is passed to the parameter CALLBACK, at least on of the columns GET or GET_LATE must be filled with "X" for each node.

    A callback routine is a subroutine defined using the following parameter interface:

    FORM subr USING node TYPE ldbcb-ldbnode
                    wa   [TYPE t]
                    evt
                    check.

    When called, the parameters are filled using the function module LDB_PROCESS and have the following meaning:

    • node contains the name of the node.
    • wa is the work area of the data read for the node. The program that calls the function module LDB_PROCESS and the program that contains the callback routine do not need to declare any interface work areas using NODES or TABLES. If the callback routine is used for one node only, the TYPE can be used to reference the data type of the node in ABAP Dictionary. Only then can the individual components of structured nodes be addressed directly in the subroutine. If the callback routine is used for multiple nodes, the TYPE addition cannot be used. In this case, the components of structured nodes can be addressed using component-by-component assignments of structures to field symbols.
    • evt contains "G" or "L", depending on whether it refers to the event GET or GET LATE. This means that the program flow can branch in accordance with the content of evt in the subroutine.
    • check enables the callback routine to modify the further processing of the program (but only if evt contains "G"). When the subroutine is called, the parameter is given the value "X". If the parameter is initial when the subroutine is exited, this indicates that the entire lower subtree is not processed using LDB_PROCESS. This is the same behavior as when a GET event block is exited using CHECK in executable programs. This option improves performance by preventing unnecessary data from being read.

    Exceptions in LDB_PROCESS

    • LDB_ALREADY_RUNNING
      A logical database cannot be called again if the current call has not yet ended.

    • LDB_NOT_REENTRANT
      A logical database can be called more than once in a row only if its database program contains the subroutine ldb_process_init.

    • LDB_SELECTIONS_NOT_ACCEPTED
      This exception can be triggered by a message in the subroutine ldb_process_check_selections. Information about this message is in the usual system fields sy-msg....

    The other exceptions are explained in the documentation of the function module.

    Executable Example

    Logical Database, Call by Function Module