SQLite

# 2014 August 16
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#
# This file implements regression tests for sessions SQLite extension.
# Specifically, this file contains tests for "patchset" changes.
#

if {![info exists testdir]} {
  set testdir [file join [file dirname [info script]] .. .. test]
} 
source [file join [file dirname [info script]] session_common.tcl]
source $testdir/tester.tcl
ifcapable !session {finish_test; return}

set testprefix sessionB

#
# 1.*: Test that the blobs returned by the session_patchset() API are 
#      as expected. Also the sqlite3_changeset_iter functions.
#
# 2.*: Test that patchset blobs are handled by sqlite3changeset_apply().
#
# 3.*: Test that sqlite3changeset_invert() works with patchset blobs. 
#      Correct behaviour is to return SQLITE_CORRUPT.

proc do_patchset_test {tn session res} {
  set r [list]
  foreach x $res {lappend r $x}
  uplevel do_test $tn [list [subst -nocommands {
    set x [list]
    sqlite3session_foreach c [$session patchset] { lappend x [set c] }
    set x
  }]] [list $r]
}

proc do_sql2patchset_test {tn sql res} {
  sqlite3session S db main
  S attach *
  execsql $sql
  uplevel [list do_patchset_test $tn S $res]
  S delete
}

#-------------------------------------------------------------------------
# Run simple tests of the _patchset() API.
#
do_execsql_test 1.0 {
  CREATE TABLE t1(a, b, c, d, PRIMARY KEY(d, a));
  INSERT INTO t1 VALUES(1, 2, 3, 4);
  INSERT INTO t1 VALUES(5, 6, 7, 8);
  INSERT INTO t1 VALUES(9, 10, 11, 12);
}

do_test 1.1 {
  sqlite3session S db main
  S attach t1
  execsql {
    INSERT INTO t1 VALUES('w', 'x', 'y', 'z');
    DELETE FROM t1 WHERE d=4;
    UPDATE t1 SET c = 14 WHERE a=5;
  }
} {}

do_patchset_test 1.2 S {
  {UPDATE t1 0 X..X {i 5 {} {} {} {} i 8} {{} {} {} {} i 14 {} {}}}
  {INSERT t1 0 X..X {} {t w t x t y t z}}
  {DELETE t1 0 X..X {i 1 {} {} {} {} i 4} {}}
}

do_test 1.3 {
  S delete
} {}

do_sql2patchset_test 1.4 {
  DELETE FROM t1;
} {
  {DELETE t1 0 X..X {i 5 {} {} {} {} i 8} {}}
  {DELETE t1 0 X..X {t w {} {} {} {} t z} {}}
  {DELETE t1 0 X..X {i 9 {} {} {} {} i 12} {}}
}

do_sql2patchset_test 1.5 {
  INSERT INTO t1 VALUES(X'61626364', NULL, NULL, 4.2);
  INSERT INTO t1 VALUES(4.2, NULL, NULL, X'61626364');
} {
  {INSERT t1 0 X..X {} {f 4.2 n {} n {} b abcd}} 
  {INSERT t1 0 X..X {} {b abcd n {} n {} f 4.2}}
}

do_sql2patchset_test 1.6 {
  UPDATE t1 SET b=45 WHERE typeof(a)=='blob';
  UPDATE t1 SET c='zzzz' WHERE typeof(a)!='blob';
} {
  {UPDATE t1 0 X..X {f 4.2 {} {} {} {} b abcd} {{} {} {} {} t zzzz {} {}}}
  {UPDATE t1 0 X..X {b abcd {} {} {} {} f 4.2} {{} {} i 45 {} {} {} {}}}
}

do_sql2patchset_test 1.7 {
  UPDATE t1 SET b='xyz' WHERE typeof(a)=='blob';
  UPDATE t1 SET c='xyz' WHERE typeof(a)!='blob';
  UPDATE t1 SET b=45 WHERE typeof(a)=='blob';
  UPDATE t1 SET c='zzzz' WHERE typeof(a)!='blob';
} {
}

do_sql2patchset_test 1.8 {
  DELETE FROM t1;
} {
  {DELETE t1 0 X..X {f 4.2 {} {} {} {} b abcd} {}} 
  {DELETE t1 0 X..X {b abcd {} {} {} {} f 4.2} {}}
}

#-------------------------------------------------------------------------
# Run simple tests of _apply() with patchset objects.
#
reset_db

proc noop {args} { error $args }
proc exec_rollback_replay {sql} {
  sqlite3session S db main
  S attach *
  execsql BEGIN
  execsql $sql
  set patchset [S patchset]
  S delete
  execsql ROLLBACK
  sqlite3changeset_apply db $patchset noop
}

do_execsql_test 2.0 {
  CREATE TABLE t2(a, b, c, d, PRIMARY KEY(b,c));
  CREATE TABLE t3(w, x, y, z, PRIMARY KEY(w));
}

do_test 2.1 {
  exec_rollback_replay {
    INSERT INTO t2 VALUES(1, 2, 3, 4);
    INSERT INTO t2 VALUES('w', 'x', 'y', 'z');
  }
  execsql { SELECT * FROM t2 }
} {1 2 3 4 w x y z}

do_test 2.2 {
  exec_rollback_replay {
    DELETE FROM t2 WHERE a=1;
    UPDATE t2 SET d = 'a';
  }
  execsql { SELECT * FROM t2 }
} {w x y a}

#-------------------------------------------------------------------------
# sqlite3changeset_invert()
#
reset_db

do_execsql_test 3.1 { CREATE TABLE t1(x PRIMARY KEY, y) }
do_test 3.2 {
  sqlite3session S db main
  S attach *
  execsql { INSERT INTO t1 VALUES(1, 2) }
  set patchset [S patchset]
  S delete
  list [catch { sqlite3changeset_invert $patchset } msg] [set msg]
} {1 SQLITE_CORRUPT}


#-------------------------------------------------------------------------
# sqlite3changeset_concat()
#
reset_db

proc do_patchconcat_test {tn args} {
  set nSql [expr [llength $args]-1]
  set res [lindex $args $nSql]
  set patchlist [list]

  execsql BEGIN
  foreach sql [lrange $args 0 end-1] {
    sqlite3session S db main
    S attach *
    execsql $sql
    lappend patchlist [S patchset]
    S delete
  }
  execsql ROLLBACK

  set patch [lindex $patchlist 0]
  foreach p [lrange $patchlist 1 end] {
    set patch [sqlite3changeset_concat $patch $p]
  }

  set x [list]
  sqlite3session_foreach c $patch { lappend x $c }

  uplevel [list do_test $tn [list set {} $x] [list {*}$res]]
}

do_execsql_test 4.1.1 {
  CREATE TABLE t1(x PRIMARY KEY, y, z);
}
do_patchconcat_test 4.1.2 {
  INSERT INTO t1 VALUES(1, 2, 3);
} {
  INSERT INTO t1 VALUES(4, 5, 6);
} {
  {INSERT t1 0 X.. {} {i 1 i 2 i 3}} 
  {INSERT t1 0 X.. {} {i 4 i 5 i 6}}
}

if 0 {
do_execsql_test 4.2.1 {
  INSERT INTO t1 VALUES(1, 2, 3);
  INSERT INTO t1 VALUES(4, 5, 6);
}
do_patchconcat_test 4.2.2 {
  UPDATE t1 SET z = 'abc' WHERE x=1
} {
  UPDATE t1 SET z = 'def' WHERE x=4
} {
}
}

finish_test

/*
** Structure for changeset iterators.
*/
struct sqlite3_changeset_iter {
  u8 *aChangeset;                 /* Pointer to buffer containing changeset */
  int nChangeset;                 /* Number of bytes in aChangeset */
  int bPatchset;                  /* True if this is a patchset */
  u8 *pNext;                      /* Pointer to next change within aChangeset */
  int rc;                         /* Iterator error code */
  sqlite3_stmt *pConflict;        /* Points to conflicting row, if any */
  char *zTab;                     /* Current table */
  int nCol;                       /* Number of columns in zTab */
  int op;                         /* Current operation */
  int bIndirect;                  /* True if current change was indirect */

** but may occur in any order (i.e. deletes, updates and inserts are all
** mixed together).
**
** Each group of changes begins with a table header:
**
**   1 byte: Constant 0x54 (capital 'T')
**   Varint: Big-endian integer set to the number of columns in the table.
**   nCol bytes: 0x01 for PK columns, 0x00 otherwise.
**   N bytes: Unqualified table name (encoded using UTF-8). Nul-terminated.
**
** Followed by one or more changes to the table.
**
**   1 byte: Either SQLITE_INSERT, UPDATE or DELETE.
**   1 byte: The "indirect-change" flag.
**   old.* record: (delete and update only)
**   new.* record: (insert and update only)
**
** PATCHSET FORMAT:
**
** A patchset is also a collection of changes. It is similar to a changeset,
** but omits those fields that are not useful if no conflict resolution
** is required when applying the changeset.
**
** Each group of changes begins with a table header:
**
**   1 byte: Constant 0x50 (capital 'P')
**   Varint: Big-endian integer set to the number of columns in the table.
**   nCol bytes: 0x01 for PK columns, 0x00 otherwise.
**   N bytes: Unqualified table name (encoded using UTF-8). Nul-terminated.
**
** Followed by one or more changes to the table.
**
**   1 byte: Either SQLITE_INSERT, UPDATE or DELETE.
**   1 byte: The "indirect-change" flag.
**   single record: (PK fields for DELETE, or full record for INSERT/UPDATE).
*/

/*
** For each row modified during a session, there exists a single instance of
** this structure stored in a SessionTable.aChange[] hash table.
*/
struct SessionChange {

**
** Otherwise, the old.* record contains all primary key values and the 
** original values of any fields that have been modified. The new.* record 
** contains the new values of only those fields that have been modified.
*/ 
static int sessionAppendUpdate(
  SessionBuffer *pBuf,            /* Buffer to append to */
  int bPatchset,                  /* True for "patchset", 0 for "changeset" */
  sqlite3_stmt *pStmt,            /* Statement handle pointing at new row */
  SessionChange *p,               /* Object containing old values */
  u8 *abPK                        /* Boolean array - true for PK columns */
){
  int rc = SQLITE_OK;
  SessionBuffer buf2 = {0,0,0}; /* Buffer to accumulate new.* record in */
  int bNoop = 1;                /* Set to zero if any values are modified */

        ){
          break;
        }
        bChanged = 1;
      }
    }

    /* If at least one field has been modified, this is not a no-op. */
    if( bChanged ) bNoop = 0;

    /* Add a field to the old.* record. This is omitted if this modules is
    ** currently generating a patchset. */
    if( bPatchset==0 ){
      if( bChanged || abPK[i] ){
        sessionAppendBlob(pBuf, pCsr, nAdvance, &rc);
      }else{
        sessionAppendByte(pBuf, 0, &rc);
      }
    }

    /* Add a field to the new.* record. Or the only record if currently
    ** generating a patchset.  */
    if( bChanged || (bPatchset && abPK[i]) ){
      sessionAppendCol(&buf2, pStmt, i, &rc);

    }else{
      sessionAppendByte(&buf2, 0, &rc);
    }

    pCsr += nAdvance;
  }

  if( bNoop ){
    pBuf->nBuf = nRewind;
  }else{
    sessionAppendBlob(pBuf, buf2.aBuf, buf2.nBuf, &rc);
  }
  sqlite3_free(buf2.aBuf);

  return rc;
}

static int sessionAppendDelete(
  SessionBuffer *pBuf,            /* Buffer to append to */
  int bPatchset,                  /* True for "patchset", 0 for "changeset" */
  sqlite3_stmt *pStmt,            /* Statement handle pointing at new row */
  SessionChange *p,               /* Object containing old values */
  u8 *abPK                        /* Boolean array - true for PK columns */
){
  int rc = SQLITE_OK;

  sessionAppendByte(pBuf, SQLITE_DELETE, &rc);
  sessionAppendByte(pBuf, p->bIndirect, &rc);

  if( bPatchset==0 ){
    sessionAppendBlob(pBuf, p->aRecord, p->nRecord, &rc);
  }else{
    int nCol = sqlite3_column_count(pStmt);
    int i;
    u8 *a = p->aRecord;
    for(i=0; i<nCol; i++){
      u8 *pStart = a;
      int eType = *a++;

      switch( eType ){
        case 0:
        case SQLITE_NULL:
          assert( abPK[i]==0 );
          break;

        case SQLITE_FLOAT:
        case SQLITE_INTEGER:
          a += 8;
          break;

        default: {
          int n;
          a += sessionVarintGet(a, &n);
          a += n;
          break;
        }
      }
      if( abPK[i] ){
        sessionAppendBlob(pBuf, pStart, a-pStart, &rc);
      }
    }
    assert( (a - p->aRecord)==p->nRecord );
  }

  return rc;
}

/*
** Formulate and prepare a SELECT statement to retrieve a row from table
** zTab in database zDb based on its primary key. i.e.

** This function is a no-op if *pRc is set to other than SQLITE_OK when it
** is called. Otherwise, append a serialized table header (part of the binary 
** changeset format) to buffer *pBuf. If an error occurs, set *pRc to an
** SQLite error code before returning.
*/
static void sessionAppendTableHdr(
  SessionBuffer *pBuf, 
  int bPatchset,
  SessionTable *pTab, 
  int *pRc
){
  /* Write a table header */
  sessionAppendByte(pBuf, (bPatchset ? 'P' : 'T'), pRc);
  sessionAppendVarint(pBuf, pTab->nCol, pRc);
  sessionAppendBlob(pBuf, pTab->abPK, pTab->nCol, pRc);
  sessionAppendBlob(pBuf, (u8 *)pTab->zName, (int)strlen(pTab->zName)+1, pRc);
}








int sessionGenerateChangeset(
  sqlite3_session *pSession,      /* Session object */
  int bPatchset,                  /* True for patchset, false for changeset */
  int *pnChangeset,               /* OUT: Size of buffer at *ppChangeset */
  void **ppChangeset              /* OUT: Buffer containing changeset */
){
  sqlite3 *db = pSession->db;     /* Source database handle */
  SessionTable *pTab;             /* Used to iterate through attached tables */
  SessionBuffer buf = {0,0,0};    /* Buffer in which to accumlate changeset */
  int rc;                         /* Return code */

      /* Check the table schema is still Ok. */
      rc = sessionTableInfo(db, pSession->zDb, zName, &nCol, 0, &azCol, &abPK);
      if( !rc && (pTab->nCol!=nCol || memcmp(abPK, pTab->abPK, nCol)) ){
        rc = SQLITE_SCHEMA;
      }

      /* Write a table header */
      sessionAppendTableHdr(&buf, bPatchset, pTab, &rc);

      /* Build and compile a statement to execute: */
      if( rc==SQLITE_OK ){
        rc = sessionSelectStmt(
            db, pSession->zDb, zName, nCol, azCol, abPK, &pSel);
      }

              int iCol;
              sessionAppendByte(&buf, SQLITE_INSERT, &rc);
              sessionAppendByte(&buf, p->bIndirect, &rc);
              for(iCol=0; iCol<nCol; iCol++){
                sessionAppendCol(&buf, pSel, iCol, &rc);
              }
            }else{
              rc = sessionAppendUpdate(&buf, bPatchset, pSel, p, abPK);
            }
          }else if( p->op!=SQLITE_INSERT ){

            rc = sessionAppendDelete(&buf, bPatchset, pSel, p, abPK);


          }
          if( rc==SQLITE_OK ){
            rc = sqlite3_reset(pSel);
          }
        }
      }

    sqlite3_free(buf.aBuf);
  }

  sqlite3_exec(db, "RELEASE changeset", 0, 0, 0);
  sqlite3_mutex_leave(sqlite3_db_mutex(db));
  return rc;
}

/*
** Obtain a changeset object containing all changes recorded by the 
** session object passed as the first argument.
**
** It is the responsibility of the caller to eventually free the buffer 
** using sqlite3_free().
*/
int sqlite3session_changeset(
  sqlite3_session *pSession,      /* Session object */
  int *pnChangeset,               /* OUT: Size of buffer at *ppChangeset */
  void **ppChangeset              /* OUT: Buffer containing changeset */
){
  return sessionGenerateChangeset(pSession, 0, pnChangeset, ppChangeset);
}

/*
** Obtain a patchset object containing all changes recorded by the 
** session object passed as the first argument.
**
** It is the responsibility of the caller to eventually free the buffer 
** using sqlite3_free().
*/
int sqlite3session_patchset(
  sqlite3_session *pSession,      /* Session object */
  int *pnPatchset,                /* OUT: Size of buffer at *ppChangeset */
  void **ppPatchset               /* OUT: Buffer containing changeset */
){
  return sessionGenerateChangeset(pSession, 1, pnPatchset, ppPatchset);
}

/*
** Enable or disable the session object passed as the first argument.
*/
int sqlite3session_enable(sqlite3_session *pSession, int bEnable){
  int ret;
  sqlite3_mutex_enter(sqlite3_db_mutex(pSession->db));

**
** If an error occurs, an SQLite error code (e.g. SQLITE_NOMEM) is returned.
** The apOut[] array may have been partially populated in this case.
*/
static int sessionReadRecord(
  u8 **paChange,                  /* IN/OUT: Pointer to binary record */
  int nCol,                       /* Number of values in record */
  u8 *abPK,                       /* Array of primary key flags, or NULL */
  sqlite3_value **apOut           /* Write values to this array */
){
  int i;                          /* Used to iterate through columns */
  u8 *aRec = *paChange;           /* Cursor for the serialized record */

  for(i=0; i<nCol; i++){
    int eType;
    if( abPK && abPK[i]==0 ) continue;
    eType = *aRec++;              /* Type of value (SQLITE_NULL, TEXT etc.) */
    assert( !apOut || apOut[i]==0 );
    if( eType ){
      if( apOut ){
        apOut[i] = sqlite3ValueNew(0);
        if( !apOut[i] ) return SQLITE_NOMEM;
      }

  /* If the iterator is already at the end of the changeset, return DONE. */
  if( p->pNext>=&p->aChangeset[p->nChangeset] ){
    return SQLITE_DONE;
  }
  aChange = p->pNext;

  if( aChange[0]=='T' || aChange[0]=='P' ){
    int nByte;                    /* Bytes to allocate for apValue */
    p->bPatchset = (aChange[0]=='P');
    aChange++;
    aChange += sessionVarintGet(aChange, &p->nCol);
    p->abPK = (u8 *)aChange;
    aChange += p->nCol;
    p->zTab = (char *)aChange;
    aChange += (sqlite3Strlen30((char *)aChange) + 1);
    

  if( p->op!=SQLITE_UPDATE && p->op!=SQLITE_DELETE && p->op!=SQLITE_INSERT ){
    return (p->rc = SQLITE_CORRUPT);
  }

  if( paRec ){ *paRec = aChange; }

  /* If this is an UPDATE or DELETE, read the old.* record. */
  if( p->op!=SQLITE_INSERT && (p->bPatchset==0 || p->op==SQLITE_DELETE) ){
    u8 *abPK = p->bPatchset ? p->abPK : 0;
    p->rc = sessionReadRecord(&aChange, p->nCol, abPK, paRec?0:p->apValue);
    if( p->rc!=SQLITE_OK ) return p->rc;
  }

  /* If this is an INSERT or UPDATE, read the new.* record. */
  if( p->op!=SQLITE_DELETE ){
    sqlite3_value **apOut = (paRec ? 0 : &p->apValue[p->nCol]);
    p->rc = sessionReadRecord(&aChange, p->nCol, 0, apOut);
    if( p->rc!=SQLITE_OK ) return p->rc;
  }

  if( pnRec ){ 
    *pnRec = (int)(aChange - *paRec); 
  }else if( p->bPatchset && p->op==SQLITE_UPDATE ){
    /* If this is an UPDATE that is part of a patchset, then all PK and
    ** modified fields are present in the new.* record. The old.* record
    ** is currently completely empty. This block shifts the PK fields from
    ** new.* to old.*, to accommodate the code that reads these arrays.  */
    int i;
    for(i=0; i<p->nCol; i++){
      assert( p->apValue[i]==0 );
      assert( p->abPK[i]==0 || p->apValue[i+p->nCol] );
      if( p->abPK[i] ){
        p->apValue[i] = p->apValue[i+p->nCol];
        p->apValue[i+p->nCol] = 0;
      }
    }
  }
  p->pNext = aChange;
  return SQLITE_ROW;
}

/*
** Advance an iterator created by sqlite3changeset_start() to the next
** change in the changeset. This function may return SQLITE_ROW, SQLITE_DONE

      }

      case SQLITE_INSERT:
      case SQLITE_DELETE: {
        int nByte;
        u8 *aEnd = &aIn[i+2];

        sessionReadRecord(&aEnd, nCol, 0, 0);
        aOut[i] = (eType==SQLITE_DELETE ? SQLITE_INSERT : SQLITE_DELETE);
        aOut[i+1] = aIn[i+1];
        nByte = (int)(aEnd - &aIn[i+2]);
        memcpy(&aOut[i+2], &aIn[i+2], nByte);
        i += 2 + nByte;
        break;
      }

            rc = SQLITE_NOMEM;
            goto finished_invert;
          }
          memset(apVal, 0, sizeof(apVal[0])*nCol*2);
        }

        /* Read the old.* and new.* records for the update change. */
        rc = sessionReadRecord(&aEnd, nCol, 0, &apVal[0]);
        if( rc==SQLITE_OK ){
          rc = sessionReadRecord(&aEnd, nCol, 0, &apVal[nCol]);
        }

        /* Write the header for the new UPDATE change. Same as the original. */
        aOut[i] = SQLITE_UPDATE;
        aOut[i+1] = aIn[i+1];
        nWrite = 2;

  assert( p->azCol && p->abPK );
  assert( !pbReplace || *pbReplace==0 );

  sqlite3changeset_op(pIter, &zDummy, &nCol, &op, 0);

  if( op==SQLITE_DELETE ){

    /* Bind values to the DELETE statement. If conflict handling is required,
    ** bind values for all columns and set bound variable (nCol+1) to true.
    ** Or, if conflict handling is not required, bind just the PK column
    ** values and, if it exists, set (nCol+1) to false. Conflict handling
    ** is not required if:
    **
    **   * this is a patchset, or
    **   * (pbRetry==0), or
    **   * all columns of the table are PK columns (in this case there is
    **     no (nCol+1) variable to bind to).
    */
    u8 *abPK = (pIter->bPatchset ? p->abPK : 0);
    rc = sessionBindRow(pIter, sqlite3changeset_old, nCol, abPK, p->pDelete);
    if( rc==SQLITE_OK && sqlite3_bind_parameter_count(p->pDelete)>nCol ){
      rc = sqlite3_bind_int(p->pDelete, nCol+1, (pbRetry==0 || abPK));
    }
    if( rc!=SQLITE_OK ) return rc;

    sqlite3_step(p->pDelete);
    rc = sqlite3_reset(p->pDelete);
    if( rc==SQLITE_OK && sqlite3_changes(p->db)==0 ){
      rc = sessionConflictHandler(

      if( pOld ){
        rc = sessionBindValue(p->pUpdate, i*3+1, pOld);
      }
      if( rc==SQLITE_OK && pNew ){
        rc = sessionBindValue(p->pUpdate, i*3+3, pNew);
      }
    }
    if( rc==SQLITE_OK ){
      sqlite3_bind_int(p->pUpdate, nCol*3+1, pbRetry==0 || pIter->bPatchset);
    }
    if( rc!=SQLITE_OK ) return rc;

    /* Attempt the UPDATE. In the case of a NOTFOUND or DATA conflict,
    ** the result will be SQLITE_OK with 0 rows modified. */
    sqlite3_step(p->pUpdate);
    rc = sqlite3_reset(p->pUpdate);

      pNew->bIndirect = (bIndirect && pExist->bIndirect);
      aCsr = pNew->aRecord = (u8 *)&pNew[1];

      if( op1==SQLITE_INSERT ){             /* INSERT + UPDATE */
        u8 *a1 = aRec;
        assert( op2==SQLITE_UPDATE );
        pNew->op = SQLITE_INSERT;
        sessionReadRecord(&a1, pTab->nCol, 0, 0);
        sessionMergeRecord(&aCsr, pTab->nCol, pExist->aRecord, a1);
      }else if( op1==SQLITE_DELETE ){       /* DELETE + INSERT */
        assert( op2==SQLITE_INSERT );
        pNew->op = SQLITE_UPDATE;
        if( 0==sessionMergeUpdate(&aCsr, pTab, pExist->aRecord, 0, aRec, 0) ){
          sqlite3_free(pNew);
          pNew = 0;
        }
      }else if( op2==SQLITE_UPDATE ){       /* UPDATE + UPDATE */
        u8 *a1 = pExist->aRecord;
        u8 *a2 = aRec;
        assert( op1==SQLITE_UPDATE );
        sessionReadRecord(&a1, pTab->nCol, 0, 0);
        sessionReadRecord(&a2, pTab->nCol, 0, 0);
        pNew->op = SQLITE_UPDATE;
        if( 0==sessionMergeUpdate(&aCsr, pTab, aRec, pExist->aRecord, a1, a2) ){
          sqlite3_free(pNew);
          pNew = 0;
        }
      }else{                                /* UPDATE + DELETE */
        assert( op1==SQLITE_UPDATE && op2==SQLITE_DELETE );

  if( rc==SQLITE_OK ){
    SessionTable *pTab;
    SessionBuffer buf = {0, 0, 0};
    for(pTab=pList; pTab; pTab=pTab->pNext){
      int i;
      if( pTab->nEntry==0 ) continue;

      sessionAppendTableHdr(&buf, 0, pTab, &rc);
      for(i=0; i<pTab->nChange; i++){
        SessionChange *p;
        for(p=pTab->apChange[i]; p; p=p->pNext){
          sessionAppendByte(&buf, p->op, &rc);
          sessionAppendByte(&buf, p->bIndirect, &rc);
          sessionAppendBlob(&buf, p->aRecord, p->nRecord, &rc);
        }

** resulting changeset will contain an UPDATE change that updates both fields.
*/
int sqlite3session_changeset(
  sqlite3_session *pSession,      /* Session object */
  int *pnChangeset,               /* OUT: Size of buffer at *ppChangeset */
  void **ppChangeset              /* OUT: Buffer containing changeset */
);

/*
** CAPI3REF: Generate A Patchset From A Session Object
*/
int sqlite3session_patchset(
  sqlite3_session *pSession,      /* Session object */
  int *pnPatchset,                /* OUT: Size of buffer at *ppChangeset */
  void **ppPatchset               /* OUT: Buffer containing changeset */
);

/*
** CAPI3REF: Test if a changeset has recorded any changes.
**
** Return non-zero if no changes to attached tables have been recorded by 
** the session object passed as the first argument. Otherwise, if one or 
** more changes have been recorded, return zero.

    { "attach",       1, "TABLE",  }, /* 0 */
    { "changeset",    0, "",       }, /* 1 */
    { "delete",       0, "",       }, /* 2 */
    { "enable",       1, "BOOL",   }, /* 3 */
    { "indirect",     1, "BOOL",   }, /* 4 */
    { "isempty",      0, "",       }, /* 5 */
    { "table_filter", 1, "SCRIPT", }, /* 6 */
    { "patchset",     0, "",       }, /* 7 */
    { 0 }
  };
  int iSub;
  int rc;

  if( objc<2 ){
    Tcl_WrongNumArgs(interp, 1, objv, "SUBCOMMAND ...");

      rc = sqlite3session_attach(pSession, zArg);
      if( rc!=SQLITE_OK ){
        return test_session_error(interp, rc);
      }
      break;
    }

    case 7:        /* patchset */
    case 1: {      /* changeset */
      int nChange;
      void *pChange;
      if( iSub==7 ){
        rc = sqlite3session_patchset(pSession, &nChange, &pChange);
      }else{
        rc = sqlite3session_changeset(pSession, &nChange, &pChange);
      }
      if( rc==SQLITE_OK ){
        Tcl_SetObjResult(interp, Tcl_NewByteArrayObj(pChange, nChange)); 
        sqlite3_free(pChange);
      }else{
        return test_session_error(interp, rc);
      }
      break;