Ü    Chain

·         The CHAIN command does a SETLL and a READE in order to find a match. CHAIN is best used to locate a unique record (like a customer record) from a full procedural file.

·         In case of CHAIN, the file operation is used to randomly retrieve a record from a file.

·        We cannot move to another record, which meets the same criteria specified in the Chain operation. So the conclusion is we cannot read more number of records with the Chain operation, if there are more number of records exists with the same criteria in the file.

·         The CHAIN operation applies a record lock to files that are open in update mode. To avoid lock we use operator extender ‘N’.

·         The search argument must be the key or key list or relative record number.

·         If the corresponding record for the search argument is not found then the HI level indicator gets turned on and if found gets turned OFF. %FOUND built-in function also does the same thing by returning '0' if no record is found and ‘1’ if a record is found.

·         To handle CHAIN exceptions (file status codes greater than 1000), either the operation code extender 'E' or an error indicator at LO level can be used.

·         If the data-structure is specified in result field then the result of the operation is filled in the data structure.

Example

I.            Using field value in factor-1 with CHAIN operation

0171.00 C     EDTSR         BEGSR
0172.00 C                   EVAL      K_PNUM=S_PNUM
0173.00 C     K_PNUM        CHAIN(E)  REC2
0174.00 C                   IF        %FOUND()
0175.00 C                   EVAL      PADDR=S_PADDR
0176.00 C                   UPDATE    REC2
0177.00 C                   ENDIF
0178.00 C                   ENDSR

II.            Using RRN value in factor-1 with CHAIN operation

0130.00 C     UPDSFL        BEGSR
0131.00 C                   EVAL      RRN=1
0132.00 C                   DO        SFLPAG
0133.00 C     RRN           CHAIN     EXPD_SFL
0134.00 C                   UPDATE    EXPD_SFL
0135.00 C                   EVAL      RRN=RRN+1
0136.00 C                   ENDDO
0137.00 C                   ENDSR

III.            Using keylist in factor-1 with CHAIN operation in FREE format RPG

  Key list
C     Klst1         KLIST
C                   Kfld                    FILED01
C                   Kfld                    FILED02
 
/FREE
 
F03RRN=0;
// Intitalise klst1
 
Chain  klst1   FILE01;
If %found(FILE01);
C#PDES=PDES;
Endif;
 
/END-FREE

IV.            Using multiple key field(including constant) in factor-1 with CHAIN operation in FREE format RPG

/FREE
 
   Chain (CO:DSREF:'3') FILE01;
   If %found(FILE01);
      Chain (FILED01:%subst(SREF01:1:7): %int(%subst(SREF01:8:3))) FILE02;
      If %found(FILE02);
         If QTAL02<>0;
            --------------
            --------------
            --------------
         Endif
      Endif;arun 
   Endif; 
 
/END-FREE

V.            Using data structure in Result-field with CHAIN operation

Columns . . . :    6  80         Browse                                      AMINEM/QRPGLESRC
SEU==>                                                                            OP_CHAINDS
FMT FX FFilename++IPEASF.....L.....A.Device+.Keywords+++++++++++++++++++++++++++++
*************** Beginning of data ***************************************************
0001.00 Fcust      IF   E             DISK                                              130128
0002.00 DDS1              DS                  LIKEREC(CUSTR)                            130128
0003.00 C     5             CHAIN     cust          DS1                                 130128
0004.00 C                   IF        %FOUND(cust)                                      130128
0005.00 C     DS1           DSPLY                                                       130128
0006.00 C                   ELSE                                                        130128
0007.00 C     'NOT FOUND'   DSPLY                                                       130128
0008.00 C                   ENDIF                                                       130128
0009.00 C                   SETON                                        LR             130128
****************** End of data *******************************************************

OUTPUT