Temporary LOBs, 12 of 29

Read Portion of Temporary LOB (substr)

Figure 10-10 Use Case Diagram: Read Portion of Temporary LOB from the Table (substr)

See:
"Use Case Model: Internal Temporary LOBs", for all basic operations of Internal Temporary LOBs.

Purpose

This procedure describes how to read portion of a temporary LOB (substr).

Usage Notes

Not applicable.

Syntax

See Chapter 3, "LOB Programmatic Environments" for a list of available functions in each programmatic environment. Use the following syntax references for each programmatic environment:

PL/SQL (DBMS_LOB): Oracle8i Supplied PL/SQL Packages Reference Chapter 18, "DBMS_LOB" -- SUBSTR
C (OCI): There is no applicable syntax reference for this use case.
COBOL (Pro*COBOL): Pro*COBOL Precompiler Programmer's Guide: Appendix F, "Embedded SQL and Precompiler Directives" -- LOB READ
C/C++ (Pro*C/C++): Pro*C/C++ Precompiler Programmer's Guide Appendix F, "Embedded SQL Statements and Directives" -- LOB LOAD. See also PL/SQL DBMS_LOB.SUBSTR.
Visual Basic (OO4O): There is no applicable syntax reference for this use case.
Java (JDBC): There is no applicable syntax reference for this use case.

Scenario

These examples show the operation in terms of reading a portion from sound-effect Sound.

Examples

Examples are provided in the following programmatic environments:

PL/SQL (DBMS_LOB Package): Read a Portion of Temporary LOB (substr)
C (OCI): No example is provided with this release.
COBOL (Pro*COBOL): Read a Portion of Temporary LOB (substr)
C/C++ (Pro*C/C++): Read a Portion of Temporary LOB (substr)
Visual Basic (OO4O): No example is provided with this release.
Java (JDBC): No example is provided with this release.

PL/SQL (DBMS_LOB Package): Read a Portion of Temporary LOB (substr)

/* Note that the example procedure substringTempLOB_proc 
   is not part of the DBMS_LOB package. */
/* This example assumes the user has a 'Washington_audio' file in a
   directory which has a AUDIO_DIR alias */
CREATE or REPLACE PROCEDURE substringTempLOB_proc IS
   Dest_loc       BLOB;
   Src_loc        BFILE := BFILENAME('AUDIO_DIR', 'Washington_audio');
   Amount         INTEGER := 32767;
   Bbuf           RAW(32767);
   Position       INTEGER :=128;
BEGIN
   DBMS_LOB.CREATETEMPORARY(Dest_loc,TRUE);
   /* Opening the FILE  is mandatory: */
   DBMS_LOB.OPEN(Src_loc, DBMS_LOB.LOB_READONLY);
   /* Opening the LOB is optional */
   DBMS_LOB.OPEN(Dest_loc,DBMS_LOB.LOB_READWRITE);
   DBMS_LOB.LOADFROMFILE(Dest_loc, Src_loc, Amount);
   Bbuf := DBMS_LOB.SUBSTR(Dest_loc, Amount, Position);
   /* Closing the LOB is mandatory if you have opened it: */
   DBMS_LOB.CLOSE(Src_loc);
   DBMS_LOB.CLOSE(Dest_loc);
END;

COBOL (Pro*COBOL): Read a Portion of Temporary LOB (substr)

       IDENTIFICATION DIVISION.
       PROGRAM-ID. ONE-READ-BLOB.
       ENVIRONMENT DIVISION.
       DATA DIVISION.
       WORKING-STORAGE SECTION.

       01  USERID         PIC X(9) VALUES "SAMP/SAMP".
       01  TEMP-BLOB      SQL-BLOB.
       01  SRC-BFILE      SQL-BFILE.
       01  DIR-ALIAS      PIC X(30) VARYING.
       01  FNAME          PIC X(20) VARYING.
       01  BUFFER2        PIC X(32767) VARYING.
       01  AMT            PIC S9(9) COMP.
       01  OFFSET         PIC S9(9) COMP VALUE 1.
       01  ORASLNRD       PIC 9(4).
       01  ISTEMP         PIC S9(9) COMP.

           EXEC SQL INCLUDE SQLCA END-EXEC.
           EXEC ORACLE OPTION (ORACA=YES) END-EXEC.
           EXEC SQL INCLUDE ORACA END-EXEC.
           EXEC SQL VAR BUFFER2 IS LONG RAW(32767) END-EXEC.

       PROCEDURE DIVISION.
       ONE-READ-BLOB.

           EXEC SQL WHENEVER SQLERROR DO PERFORM SQL-ERROR END-EXEC.
           EXEC SQL
                CONNECT :USERID
           END-EXEC.

      * Allocate and initialize the BLOB locator
           EXEC SQL ALLOCATE :SRC-BFILE END-EXEC.
           EXEC SQL ALLOCATE :TEMP-BLOB END-EXEC.
           EXEC SQL LOB CREATE TEMPORARY :TEMP-BLOB END-EXEC. 
           EXEC SQL WHENEVER NOT FOUND GOTO END-OF-BLOB END-EXEC.
  
      * Set up the directory and file information
           MOVE "AUDIO_DIR" TO DIR-ALIAS-ARR.
           MOVE 9 TO DIR-ALIAS-LEN.
           MOVE "Washington_audio" TO FNAME-ARR.
           MOVE 16 TO FNAME-LEN.

           EXEC SQL
              LOB FILE SET :SRC-BFILE DIRECTORY = :DIR-ALIAS,
              FILENAME = :FNAME
           END-EXEC.

           EXEC SQL 
              LOB DESCRIBE :SRC-BFILE GET LENGTH INTO :AMT
           END-EXEC.

      * Open source BFILE and destination temporary BLOB.
           EXEC SQL LOB OPEN :SRC-BFILE READ ONLY END-EXEC.
           EXEC SQL LOB OPEN :TEMP-BLOB READ WRITE END-EXEC.
           
           EXEC SQL
                LOB LOAD :AMT FROM FILE :SRC-BFILE INTO :TEMP-BLOB
           END-EXEC.
 
      * Perform a single read

           EXEC SQL 
                LOB READ :AMT FROM :TEMP-BLOB INTO :BUFFER2 
           END-EXEC.
          
           DISPLAY "Read ", BUFFER2, " from TEMP-BLOB".

       END-OF-BLOB.
           EXEC SQL LOB CLOSE :TEMP-BLOB END-EXEC.
           EXEC SQL LOB CLOSE :SRC-BFILE END-EXEC.
           EXEC SQL LOB FREE TEMPORARY :TEMP-BLOB END-EXEC.
           EXEC SQL FREE :TEMP-BLOB END-EXEC.
           EXEC SQL FREE :SRC-BFILE END-EXEC.
           STOP RUN.
        
       SQL-ERROR.
           EXEC SQL
               WHENEVER SQLERROR CONTINUE
           END-EXEC.
           MOVE ORASLNR TO ORASLNRD.
           DISPLAY " ".
           DISPLAY "ORACLE ERROR DETECTED ON LINE ", ORASLNRD, ":".
           DISPLAY " ".
           DISPLAY SQLERRMC.
           EXEC SQL
               ROLLBACK WORK RELEASE
           END-EXEC.
           STOP RUN.

C/C++ (Pro*C/C++): Read a Portion of Temporary LOB (substr)

/* Pro*C/C++ lacks an equivalent embedded SQL form for the DBMS_LOB.SUBSTR()
   function.  However, Pro*C/C++ can interoperate with PL/SQL using
   anonymous PL/SQL blocks embedded in a Pro*C/C++ program as this example
   shows. */

#include <oci.h>
#include <stdio.h>
#include <sqlca.h>

void Sample_Error()
{
  EXEC SQL WHENEVER SQLERROR CONTINUE;
  printf("%.*s\n", sqlca.sqlerrm.sqlerrml, sqlca.sqlerrm.sqlerrmc);
  EXEC SQL ROLLBACK WORK RELEASE;
  exit(1);
}

#define BufferLength 4096

void substringTempLOB_proc()
{
  OCIBlobLocator *Temp_loc;
  OCIBFileLocator *Lob_loc;
  char *Dir = "AUDIO_DIR", *Name = "Washington_audio";
  int Position = 1024;
  unsigned int Length;
  int Amount = BufferLength;
  struct {
    unsigned short Length;
    char Data[BufferLength];
  } Buffer;
  /* Datatype Equivalencing is Mandatory for this Datatype: */
  EXEC SQL VAR Buffer IS VARRAW(BufferLength);

  EXEC SQL WHENEVER SQLERROR DO Sample_Error();
  /* Allocate and Create the Temporary LOB: */
  EXEC SQL ALLOCATE :Temp_loc;
  EXEC SQL LOB CREATE TEMPORARY :Temp_loc;
  /* Allocate and Initialize the BFILE Locator: */
  EXEC SQL ALLOCATE :Lob_loc;
  EXEC SQL LOB FILE SET :Lob_loc DIRECTORY = :Dir, FILENAME = :Name;
  /* Open the LOBs: */
  EXEC SQL LOB OPEN :Lob_loc READ ONLY;
  EXEC SQL LOB OPEN :Temp_loc READ WRITE;
  /* Determine the length of the BFILE and load it into the Temporary LOB: */
  EXEC SQL LOB DESCRIBE :Lob_loc GET LENGTH INTO :Length;
  EXEC SQL LOB LOAD :Length FROM FILE :Lob_loc INTO :Temp_loc;
  /* Invoke SUBSTR() on the Temporary LOB inside a PL/SQL block: */
  EXEC SQL EXECUTE
    BEGIN
      :Buffer := DBMS_LOB.SUBSTR(:Temp_loc, :Amount, :Position);
    END;
  END-EXEC;
  /* Process the Data in the Buffer. */
  /* Closing the LOBs is Mandatory if they have been Opened: */
  EXEC SQL LOB CLOSE :Lob_loc;
  EXEC SQL LOB CLOSE :Temp_loc;
  /* Free the Temporary LOB: */
  EXEC SQL LOB FREE TEMPORARY :Temp_loc;
  /* Release resources used by the locators: */
  EXEC SQL FREE :Lob_loc;
  EXEC SQL FREE :Temp_loc;
}

void main()
{
  char *samp = "samp/samp";
  EXEC SQL CONNECT :samp;
  substringTempLOB_proc();
  EXEC SQL ROLLBACK WORK RELEASE;

}