１、概覽
通過LDB_PROCESS函數可以允許任何程序訪問邏輯數據庫，允許一個程序訪問多個邏輯數據庫，當然也允許多次連續訪問訪問同個邏輯數據庫。當使用LDB_PROCESS函數來訪問邏輯數據庫時，選擇屏幕將不顯示，其選擇參數由FIELD_SELECTION參數傳入。

2、LDB_PROCESS參數說明
LDBNAME
Name of the logical database you want to call.

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

EXPRESSIONS
In this parameter, you can pass extra selections for the nodes of the logical database for which dynamic selections are allowed. 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 you use the WITH FREE SELECTION addition in a SUBMIT statement.

FIELD_SELECTION
You can use this parameter to pass a list of the required fields for the nodes of the logical database for which dynamic selections are allowed. The data type of the parameter is the deep internal table RSFS_FIELDS, defined in the type group RSFS. The component TABLENAME contains the name of the node and the deep component FIELDS contains the names of the fields that you want to read.

The function module has the following tables parameters:

CALLBACK
You use this parameter to assign callback routines to the names of nodes and events. The parameter determines the nodes of the logical database for which data is read, and when the data is passed back to the program and in which callback routine.

SELECTIONS
You can use this parameter to pass input values for the fields of the selection screen of the logical database. The data type of the parameter corresponds to the structure RSPARAMS in the ABAP Dictionary. The data is passed in the same way as when you use the WITH SELECTION-TABLE addition in a SUBMIT statement.

3、LDB_PROCESS的CALLBACK回調參數的具體字段的說明
LDBNODE
Name of the node of the logical database to be read.

GET
A flag (contents X or SPACE), to call the corresponding callback routine at the GET event.

GET_LATE
A flag (contents X or SPACE), to call the corresponding callback routine at the GET LATE event.

CB_PROG
Name of the ABAP program in which the callback routine is defined.

CB_FORM
Name of the callback routine.

４、回調函數的編寫
回調子程序的標準形式
FORM <subr> USING <node> LIKE LDBCB-LDBNODE
????????????????? <wa>?? [TYPE <t>]
????????????????? <evt>
????????????????? <check>.
......
ENDFORM.
其中參數說明作用:
<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 containing the callback routine do not have to declare interface work areas using NODES or TABLES. If the callback routine is only used for one node, you can use a TYPE reference to refer to the data type of the node in the ABAP Dictionary. Only then can you address the individual components of structured nodes directly in the subroutine. If you use the callback routine for more than one node, you cannot use a TYPE reference. In this case, you would have to address the components of structured nodes by assigning them one by one to a field symbol.
<evt> contains G or L, for GET or GET LATE respectively. This means that the subroutine can direct the program flow using the contents of <evt>.
<check> allows the callback routine to influence how the program is processed further (but only if <evt> contains the value G). The value X is assigned to the parameter when the subroutine is called. If it has the value SPACE when the subroutine ends, this flags that the subordinate nodes of the logical database should not be processed in the function module LDB_PROCESS. This is the same as leaving a GET event block using CHECK in an executable program. If this prevents unnecessary data from being read, it will improve the performance of your program.

５、樣例代碼及說明
TABLES SPFLI.
SELECT-OPTIONS S_CARR FOR SPFLI-CARRID.

TYPE-POOLS: RSDS, RSFS.

DATA: CALLBACK TYPE TABLE OF LDBCB,
　　??? CALLBACK_WA LIKE LINE OF CALLBACK.

DATA: SELTAB TYPE TABLE OF RSPARAMS,
????? SELTAB_WA LIKE LINE OF SELTAB.

DATA: TEXPR TYPE RSDS_TEXPR,
????? FSEL? TYPE RSFS_FIELDS.

*設置需要回調的數據節點和回調對應的子程序
CALLBACK_WA-LDBNODE???? = 'SPFLI'.
CALLBACK_WA-GET???????? = 'X'.
CALLBACK_WA-GET_LATE??? = 'X'.
CALLBACK_WA-CB_PROG???? = SY-REPID.
CALLBACK_WA-CB_FORM???? = 'CALLBACK_SPFLI'.
APPEND CALLBACK_WA TO CALLBACK.

CLEAR CALLBACK_WA.
CALLBACK_WA-LDBNODE???? = 'SFLIGHT'.
CALLBACK_WA-GET???????? = 'X'.
CALLBACK_WA-CB_PROG???? = SY-REPID.
CALLBACK_WA-CB_FORM???? = 'CALLBACK_SFLIGHT'.
APPEND CALLBACK_WA TO CALLBACK.

*設置對應的選擇屏幕的參數的傳入值
SELTAB_WA-KIND = 'S'.
SELTAB_WA-SELNAME = 'CARRID'.

LOOP AT S_CARR.
? MOVE-CORRESPONDING S_CARR TO SELTAB_WA.
? APPEND SELTAB_WA TO SELTAB.
ENDLOOP.

*調用函數
CALL FUNCTION 'LDB_PROCESS'
???? EXPORTING
????????? LDBNAME???????????????????? = 'F1S'
????????? VARIANT???????????????????? = ' '
????????? EXPRESSIONS???????????????? = TEXPR
????????? FIELD_SELECTION???????????? = FSEL
???? TABLES
????????? CALLBACK??????????????????? = CALLBACK
????????? SELECTIONS????????????????? = SELTAB
???? EXCEPTIONS
????????? LDB_NOT_REENTRANT?????????? = 1
????????? LDB_INCORRECT?????????????? = 2
????????? LDB_ALREADY_RUNNING???????? = 3
????????? LDB_ERROR?????????????????? = 4
????????? LDB_SELECTIONS_ERROR??????? = 5
????????? LDB_SELECTIONS_NOT_ACCEPTED = 6
????????? VARIANT_NOT_EXISTENT??????? = 7
????????? VARIANT_OBSOLETE??????????? = 8
????????? VARIANT_ERROR?????????????? = 9
????????? FREE_SELECTIONS_ERROR?????? = 10
????????? CALLBACK_NO_EVENT?????????? = 11
????????? CALLBACK_NODE_DUPLICATE???? = 12
????????? OTHERS????????????????????? = 13.

IF SY-SUBRC <> 0.
? WRITE: 'Exception with SY-SUBRC', SY-SUBRC.
ENDIF.

*SPFLI節點對應的回調處理函數
FORM CALLBACK_SPFLI USING NAME? TYPE LDBN-LDBNODE
????????????????????????? WA??? TYPE SPFLI
????????????????????????? EVT?? TYPE C
????????????????????????? CHECK TYPE C.
? CASE EVT.
?? WHEN 'G'.
????? WRITE: / WA-CARRID, WA-CONNID, WA-CITYFROM, WA-CITYTO.
????? ULINE.
??? WHEN 'L'.
????? ULINE.
? ENDCASE.
ENDFORM.

*SFIGHT節點對應的回調處理函數
FORM CALLBACK_SFLIGHT USING NAME? TYPE LDBN-LDBNODE
??????????????????????????? WA??? TYPE SFLIGHT
??????????????????????????? EVT?? TYPE C
??????????????????????????? CHECK TYPE C.
? WRITE: / WA-FLDATE, WA-SEATSOCC, WA-SEATSMAX.
ENDFORM.

注意：通過'LDB_PROCESS'函數訪問邏輯數據庫時，請不要在程序屬性里綁定邏輯數據庫，否則會出LDB_ALREADY_RUNNING錯誤。
資料來源sap library.

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