Oracle9i Application Developer's Guide - Large Objects (LOBs)
Release 1 (9.0.1)
Part Number A88879-01
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Internal Persistent LOBs, 27 of 43

Equality: Checking If One LOB Locator Is Equal to Another

Figure 10-31 Use Case Diagram: Checking If One LOB Locator Is Equal to Another


Text description of adl10p36.gif follows This link takes you back to the Internal Persistent LOB main diagram.
Text description of the illustration adl10p36.gif

See:

"Use Case Model: Internal Persistent LOBs Operations", for all Internal Persistent LOB operations. 

Purpose

This procedure describes how to see if one LOB locator is equal to another.

Usage Notes

Not applicable.

Syntax

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

Scenario

If two locators are equal, this means that they refer to the same version of the LOB data (see "Read Consistent Locators"). In this example, the locators are equal. However, it may be as important to determine that locators do not refer to same version of the LOB data.

Examples

Examples are provided in the following programmatic environments:

C (OCI): Checking If One LOB Locator Is Equal to Another

This script is also located at $ORACLE_HOME/rdbms/demo/lobs/oci/iequal. 

/* Select the locator: */
sb4 select_lock_frame_locator(Lob_loc, errhp, svchp, stmthp)
OCILobLocator *Lob_loc;
OCIError      *errhp;
OCISvcCtx     *svchp;
OCIStmt       *stmthp;     
{
  text  *sqlstmt = 
    (text *)"SELECT Frame FROM Multimedia_tab WHERE Clip_ID=1 FOR UPDATE";
  OCIDefine *defnp1;
  checkerr (errhp, OCIStmtPrepare(stmthp, errhp, sqlstmt, 
                                  (ub4)strlen((char *)sqlstmt),
                                  (ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT));
  checkerr (errhp, OCIDefineByPos(stmthp, &defnp1, errhp, (ub4) 1,
                                  (dvoid *)&Lob_loc, (sb4)0, 
                                  (ub2) SQLT_BLOB,(dvoid *) 0, 
                                  (ub2 *) 0, (ub2 *) 0, (ub4) OCI_DEFAULT));

  /* Execute the select and fetch one row: */
  checkerr(errhp, OCIStmtExecute(svchp, stmthp, errhp, (ub4) 1, (ub4) 0,
                                 (CONST OCISnapshot*) 0, (OCISnapshot*) 0,  
                                 (ub4) OCI_DEFAULT));
  return (0);
}
void locatorIsEqual(envhp, errhp, svchp, stmthp)
OCIEnv    *envhp;
OCIError  *errhp;
OCISvcCtx *svchp;
OCIStmt   *stmthp;
{
  OCILobLocator *dest_loc, *src_loc;
  boolean       isEqual;

  /* Allocate the LOB locators: */
  (void) OCIDescriptorAlloc((dvoid *) envhp, (dvoid **) &dest_loc,
                            (ub4)OCI_DTYPE_LOB, (size_t) 0, (dvoid **) 0);
  (void) OCIDescriptorAlloc((dvoid *) envhp, (dvoid **) &src_loc, 
                            (ub4)OCI_DTYPE_LOB, (size_t) 0, (dvoid **) 0);

  /* Select the LOBs: */
  printf (" select and lock a frame locator\n");
  select_lock_frame_locator(src_loc, errhp, svchp, stmthp);/* source locator */
 
  /* Assign src_loc to dest_loc thereby saving a copy of the value of the LOB
     at this point in time: */
  printf(" assign the src locator to dest locator\n");
  checkerr (errhp, OCILobAssign(envhp, errhp, src_loc, &dest_loc)); 

  /* When you write some data to the LOB through Lob_loc1, Lob_loc2 will not
     see the newly written data whereas Lob_loc1 will see the new data: */

  /* Call OCI to see if the two locators are Equal: */

  printf (" check if Lobs are Equal.\n");
  checkerr (errhp, OCILobIsEqual(envhp, src_loc, dest_loc, &isEqual));

  if (isEqual)
  {
    /* ... The LOB locators are Equal: */
    printf(" Lob Locators are equal.\n");
  }
  else
  {
    /* ... The LOB locators are not Equal: */
    printf(" Lob Locators are NOT Equal.\n");
  }

  /* Note that in this example, the LOB locators will be Equal */

  /* Free resources held by the locators: */
  (void) OCIDescriptorFree((dvoid *) dest_loc, (ub4) OCI_DTYPE_LOB);
  (void) OCIDescriptorFree((dvoid *) src_loc, (ub4) OCI_DTYPE_LOB);
  
  return;
}

C/C++ (Pro*C/C++): Checking If One LOB Locator Is Equal to Another

You can find this script at $ORACLE_HOME/rdbms/demo/lobs/proc/iequal 

/* Pro*C/C++ does not provide a mechanism to test the equality of two
   locators.  However, by using the OCI directly, two locators can be
   compared to determine whether or not they are equal as this example
   demonstrates: */

#include <sql2oci.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);
}

void LobLocatorIsEqual_proc()
{
  OCIBlobLocator *Lob_loc1, *Lob_loc2;
  OCIEnv *oeh;
  boolean isEqual;
  EXEC SQL WHENEVER SQLERROR DO Sample_Error();
  EXEC SQL ALLOCATE :Lob_loc1;
  EXEC SQL ALLOCATE :Lob_loc2;
  EXEC SQL SELECT Frame INTO Lob_loc1
           FROM Multimedia_tab where Clip_ID = 1 FOR UPDATE;
  /* Assign Lob_loc1 to Lob_loc2 thereby saving a copy of the value of the
     LOB at this point in time: */
  EXEC SQL LOB ASSIGN :Lob_loc1 TO :Lob_loc2;
  /* When you write some data to the lob through Lob_loc1, Lob_loc2 will
     not see the newly written data whereas Lob_loc1 will see the new
     data. */
  /* Get the OCI Environment Handle using a SQLLIB Routine: */
  (void) SQLEnvGet(SQL_SINGLE_RCTX, &oeh);
  /* Call OCI to see if the two locators are Equal: */
  (void) OCILobIsEqual(oeh, Lob_loc1, Lob_loc2, &isEqual);
  if (isEqual)
    printf("The locators are equal\n");
  else
    printf("The locators are not equal\n");
  /* Note that in this example, the LOB locators will be Equal */
  EXEC SQL FREE :Lob_loc1;
  EXEC SQL FREE :Lob_loc2;
}

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

Java (JDBC): Checking If One LOB Locator Is Equal to Another

This script is also located at $ORACLE_HOME/rdbms/demo/lobs/java/iequal. 

import java.sql.Connection;
import java.sql.Types;
import java.sql.Statement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

// Oracle Specific JDBC classes: 
import oracle.sql.*;
import oracle.jdbc.driver.*;

public class Ex2_108
{
 public static void main (String args [])
       throws Exception
  {
    // Load the Oracle JDBC driver: 
    DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());

    // Connect to the database: 
    Connection conn =
      DriverManager.getConnection ("jdbc:oracle:oci8:@", "samp", "samp");

    // It's faster when auto commit is off: 
    conn.setAutoCommit (false);

    // Create a Statement: 
    Statement stmt = conn.createStatement ();
    try
    {
      BLOB lob_loc1 = null;
      BLOB lob_loc2 = null;
      ResultSet rset = stmt.executeQuery (
          "SELECT sound FROM multimedia_tab WHERE clip_id = 2");
   if (rset.next())
   {
     lob_loc1 = ((OracleResultSet)rset).getBLOB (1);
   }

   // When you write data to LOB through lob_loc1,lob_loc2 will not see the 
changes: 
   lob_loc2 = lob_loc1;

   // Note that in this example, the Locators will be equal.
   if (lob_loc1.equals(lob_loc2))  
   {
      // The Locators are equal: 
      System.out.println("Locators are equal");
   }
   else 
   {
      // The Locators are different: 
      System.out.println("Locators are NOT equal");
   }

   stmt.close();
   conn.commit();
   conn.close();

    }
    catch (SQLException e)
    {
       e.printStackTrace();
    }
  }
}
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