Adding upstream version 3.40.1.upstream/3.40.1 upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
author: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-05-05 17:28:19 +0000
committer: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-05-05 17:28:19 +0000
commit: 18657a960e125336f704ea058e25c27bd3900dcb (patch)
tree: 17b438b680ed45a996d7b59951e6aa34023783f2 /www/sessionintro.html
parent: Initial commit. (diff)
download: sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.tar.xz
sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.zip
1 files changed, 649 insertions, 0 deletions
diff --git a/www/sessionintro.html b/www/sessionintro.html
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+<!DOCTYPE html>
+<html><head>
+<meta name="viewport" content="width=device-width, initial-scale=1.0">
+<meta http-equiv="content-type" content="text/html; charset=UTF-8">
+<link href="sqlite.css" rel="stylesheet">
+<title>The Session Extension</title>
+<!-- path= -->
+</head>
+<body>
+<div class=nosearch>
+<a href="index.html">
+<img class="logo" src="images/sqlite370_banner.gif" alt="SQLite" border="0">
+</a>
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+var w = document.getElementById(nm);
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+w.style.display = "none";
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+var w = document.getElementById("searchmenu");
+if( w.style.display=="block" ){
+w.style.display = "none";
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+document.getElementById("searchbox").focus()
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+if( x.style.display!='none' ){
+x.style.display = 'none';
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+</script>
+<div class=fancy>
+<div class=nosearch>
+<div class="fancy_title">
+The Session Extension
+</div>
+<div class="fancy_toc">
+<a onclick="toggle_toc()">
+<span class="fancy_toc_mark" id="toc_mk">&#x25ba;</span>
+Table Of Contents
+</a>
+<div id="toc_sub"><div class="fancy-toc1"><a href="#introduction">1. Introduction</a></div>
+<div class="fancy-toc2"><a href="#typical_use_case">1.1. Typical Use Case</a></div>
+<div class="fancy-toc2"><a href="#obtaining_the_session_extension">1.2. Obtaining the Session Extension</a></div>
+<div class="fancy-toc2"><a href="#limitations">1.3. Limitations</a></div>
+<div class="fancy-toc1"><a href="#concepts">2. Concepts</a></div>
+<div class="fancy-toc2"><a href="#changesets_and_patchsets">2.1. Changesets and Patchsets</a></div>
+<div class="fancy-toc2"><a href="#conflicts">2.2. Conflicts</a></div>
+<div class="fancy-toc2"><a href="#changeset_construction">2.3. Changeset Construction</a></div>
+<div class="fancy-toc1"><a href="#using_the_session_extension">3. Using The Session Extension</a></div>
+<div class="fancy-toc2"><a href="#capturing_a_changeset">3.1. Capturing a Changeset</a></div>
+<div class="fancy-toc2"><a href="#applying_a_changeset_to_a_database">3.2. Applying a Changeset to a Database</a></div>
+<div class="fancy-toc2"><a href="#inspecting_the_contents_of_a_changeset">3.3. Inspecting the Contents of a Changeset</a></div>
+<div class="fancy-toc1"><a href="#extended_functionality">4. Extended Functionality</a></div>
+</div>
+</div>
+<script>
+function toggle_toc(){
+var sub = document.getElementById("toc_sub")
+var mk = document.getElementById("toc_mk")
+if( sub.style.display!="block" ){
+sub.style.display = "block";
+mk.innerHTML = "&#x25bc;";
+} else {
+sub.style.display = "none";
+mk.innerHTML = "&#x25ba;";
+}
+}
+</script>
+</div>
+
+
+
+
+
+<h1 id="introduction"><span>1. </span>Introduction</h1>
+
+<p>The session extension provide a mechanism for recording changes
+to some or all of the <a href="rowidtable.html">rowid tables</a> in an SQLite database, and packaging
+those changes into a "changeset" or "patchset" file that can later
+be used to apply the same set of changes to another database with
+the same schema and compatible starting data.  A "changeset" may
+also be inverted and used to "undo" a session.
+
+</p><p>This document is an introduction to the session extension.
+The details of the interface are in the separate
+<a href="session/intro.html">Session Extension C-language Interface</a> document.
+
+</p><h2 id="typical_use_case"><span>1.1. </span>Typical Use Case</h2>
+
+<p>Suppose SQLite is used as the <a href="appfileformat.html">application file format</a> for a
+particular design application.  Two users, Alice and Bob, each start
+with a baseline design that is about a gigabyte in size.  They work
+all day, in parallel, each making their own customizations and tweaks
+to the design.  At the end of the day, they would like to merge their
+changes together into a single unified design.
+
+</p><p>The session extension facilitates this by recording all changes to
+both Alice's and Bob's databases and writing those changes into
+changeset or patchset files.  At the end of the day, Alice can send her
+changeset to Bob and Bob can "apply" it to his database.  The result (assuming
+there are no conflicts) is that Bob's database then contains both his
+changes and Alice's changes.  Likewise, Bob can send a changeset of
+his work over to Alice and she can apply his changes to her database.
+
+</p><p>In other words, the session extension provides a facility for
+SQLite database files that is similar to the unix
+<a href="https://en.wikipedia.org/wiki/Patch_(Unix)">patch</a> utility program,
+or to the "merge" capabilities of version control systems such
+as <a href="https://www.fossil-scm.org/">Fossil</a>, <a href="https://git-scm.com">Git</a>, 
+or <a href="http://www.mercurial-scm.org/">Mercurial</a>.
+
+</p><h2 id="obtaining_the_session_extension"><span>1.2. </span>Obtaining the Session Extension</h2>
+
+<p> Since <a href="releaselog/3_13_0.html">version 3.13.0</a> (2016-05-18), 
+the session extension has been included in the SQLite
+<a href="amalgamation.html">amalgamation</a> source distribution. By default, the session extension is 
+disabled. To enable it, build with the following compiler switches:
+
+</p><div class="codeblock"><pre>-DSQLITE_ENABLE_SESSION -DSQLITE_ENABLE_PREUPDATE_HOOK
+</pre></div>
+
+<p> Or, if using the autoconf build system, pass the --enable-session option to the configure script.
+
+</p><h2 id="limitations"><span>1.3. </span>Limitations</h2>
+
+<ul>
+
+<li><p> Prior to SQLite version 3.17.0, the session extension only worked with
+        <a href="rowidtable.html">rowid tables</a>, not <a href="withoutrowid.html">WITHOUT ROWID</a> tables. As of 3.17.0, both
+        rowid and WITHOUT ROWID tables are supported.
+
+</p></li><li><p> There is no support for <a href="vtab.html">virtual tables</a>. Changes to virtual tables are
+        not captured.
+
+</p></li><li><p> The session extension only works with tables that have a declared
+        PRIMARY KEY. The PRIMARY KEY of a table may be an INTEGER PRIMARY KEY
+        (rowid alias) or an external PRIMARY KEY.
+
+</p></li><li><p> SQLite allows <a href="nulls.html">NULL values</a> to be stored in
+        PRIMARY KEY columns. However, the session extension ignores all
+        such rows. No changes affecting rows with one or more NULL values
+        in PRIMARY KEY columns are recorded by the sessions module.
+</p></li></ul>
+
+<h1 id="concepts"><span>2. </span>Concepts</h1>
+
+<a name="changeset"></a>
+
+<h2 id="changesets_and_patchsets"><span>2.1. </span>Changesets and Patchsets</h2>
+<p> The sessions module revolves around creating and manipulating 
+changesets. A changeset is a blob of data that encodes a series of 
+changes to a database. Each change in a changeset is one of the 
+following:
+
+</p><ul>
+  <li> <p>An <b>INSERT</b>. An INSERT change contains a single row to add to 
+       a database table. The payload of the INSERT change consists of the
+       values for each field of the new row.
+
+  </p></li><li> <p>A <b>DELETE</b>. A DELETE change represents a row, identified by
+       its primary key values, to remove from a database table. The payload
+       of a DELETE change consists of the values for all fields of the 
+       deleted row.
+
+  </p></li><li> <p>An <b>UPDATE</b>. An UPDATE change represents the modification of
+       one or more non-PRIMARY KEY fields of a single row within a database 
+       table, identified by its PRIMARY KEY fields. The payload for an UPDATE
+       change consists of:
+   </p><ul>
+     <li> The PRIMARY KEY values identifying the modified row, 
+     </li><li> The new values for each modified field of the row, and
+     </li><li> The original values for each modified field of the row.
+   </li></ul>
+       <p> An UPDATE change does not contain any information regarding
+       non-PRIMARY KEY fields that are not modified by the change. It is not
+       possible for an UPDATE change to specify modifications to PRIMARY 
+       KEY fields. 
+</p></li></ul>
+
+<p> A single changeset may contain changes that apply to more than one 
+database table. For each table that the changeset includes at least one change
+for, it also encodes the following data:
+
+</p><ul>
+  <li> The name of the database table, 
+  </li><li> The number of columns the table has, and
+  </li><li> Which of those columns are PRIMARY KEY columns.
+</li></ul>
+
+<p> Changesets may only be applied to databases that contain tables 
+matching the above three criteria as stored in the changeset.
+
+</p><p> A patchset is similar to a changeset. It is slightly more compact than
+a changeset, but provides more limited conflict detection and resolution
+options (see the next section for details). The differences between a 
+patchset and a changeset are that:
+
+</p><ul>
+  <li><p> For a <b>DELETE</b> change, the payload consists of the PRIMARY KEY 
+          fields only. The original values of other fields are not stored as
+          part of a patchset.
+
+  </p></li><li><p> For an <b>UPDATE</b> change, the payload consists of the PRIMARY KEY 
+          fields and the new values of modified fields only. The original
+          values of modified fields are not stored as part of a patchset.
+</p></li></ul>
+
+<h2 id="conflicts"><span>2.2. </span>Conflicts</h2>
+
+<p> When a changeset or patchset is applied to a database, an attempt is 
+made to insert a new row for each INSERT change, remove a row for each
+DELETE change and modify a row for each UPDATE change. If the target 
+database is in the same state as the original database that the changeset
+was recorded on, this is a simple matter. However, if the contents of the
+target database is not in exactly this state, conflicts can occur when
+applying the changeset or patchset.
+
+</p><p>When processing an <b>INSERT</b> change, the following conflicts can
+occur:
+
+</p><ul>
+  <li> The target database may already contain a row with the same PRIMARY
+       KEY values as specified by the INSERT change.
+
+  </li><li> Some other database constraint, for example a UNIQUE or CHECK 
+       constraint, may be violated when the new row is inserted.
+</li></ul>
+
+<p>When processing a <b>DELETE</b> change, the following conflicts may be
+detected:
+
+</p><ul>
+  <li> The target database may contain no row with the specified PRIMARY 
+       KEY values to delete.
+
+  </li><li> The target database may contain a row with the specified PRIMARY
+       KEY values, but the other fields may contain values that do not
+       match those stored as part of the changeset. This type of conflict
+       is not detected when using a patchset.
+</li></ul>
+
+<p>When processing an <b>UPDATE</b> change, the following conflicts may be
+detected:
+
+</p><ul>
+  <li> The target database may contain no row with the specified PRIMARY 
+       KEY values to modify.
+
+  </li><li> The target database may contain a row with the specified PRIMARY
+       KEY values, but the current values of the fields that will be modified
+       by the change may not match the original values stored within the
+       changeset. This type of conflict is not detected when using a patchset.
+
+  </li><li> Some other database constraint, for example a UNIQUE or CHECK 
+       constraint, may be violated when the row is updated.
+</li></ul>
+
+<p> Depending on the type of conflict, a sessions application has a variety
+of configurable options for dealing with conflicts, ranging from omitting the
+conflicting change, aborting the entire changeset application or applying
+the change despite the conflict. For details, refer to the documentation for
+the <a href="session/sqlite3changeset_apply.html">sqlite3changeset_apply()</a> API.
+
+</p><h2 id="changeset_construction"><span>2.3. </span>Changeset Construction</h2>
+
+<p> After a session object has been configured, it begins monitoring for 
+changes to its configured tables. However, it does not record an entire
+change each time a row within the database is modified. Instead, it records
+just the PRIMARY KEY fields for each inserted row, and just the PRIMARY KEY 
+and all original row values for any updated or deleted rows. If a row is 
+modified more than once by a single session, no new information is recorded.
+
+</p><p> The other information required to create a changeset or patchset is
+read from the database file when <a href="session/sqlite3session_changeset.html">sqlite3session_changeset()</a> or
+<a href="session/sqlite3session_patchset.html">sqlite3session_patchset()</a> is called. Specifically,
+
+</p><ul>
+  <li> <p>For each primary key recorded as a result of an INSERT operation, 
+       the sessions module checks if there is a row with a matching primary
+       key still in the table. If so, an INSERT change is added to the 
+       changeset.
+
+  </p></li><li> <p>For each primary key recorded as a result of an UPDATE or DELETE
+       operation, the sessions module also checks for a row with a matching
+       primary key within the table. If one can be found, but one or more
+       of the non-PRIMARY KEY fields does not match the original recorded
+       value, an UPDATE is added to the changeset. Or, if there is no row
+       at all with the specified primary key, a DELETE is added to the 
+       changeset. If the row does exist but none of the non-PRIMARY KEY
+       fields have been modified, no change is added to the changeset.
+</p></li></ul>
+
+<p> One implication of the above is that if a change is made and then 
+unmade within a single session (for example if a row is inserted and then
+deleted again), the sessions module does not report any change at all. Or
+if a row is updated multiple times within the same session, all updates
+are coalesced into a single update within any changeset or patchset blob.
+
+</p><h1 id="using_the_session_extension"><span>3. </span>Using The Session Extension</h1>
+
+<p> This section provides examples that demonstrate how to use the sessions
+    extension.
+
+</p><h2 id="capturing_a_changeset"><span>3.1. </span>Capturing a Changeset</h2>
+
+<p> The example code below demonstrates the steps involved in capturing a
+changeset while executing SQL commands. In summary:
+
+</p><ol>
+  <li> <p>A session object (type sqlite3_session*) is created by making a 
+          call to the <a href="session/sqlite3session_create.html">sqlite3session_create()</a> API function.
+
+       </p><p>A single session object monitors changes made to a single database 
+          (i.e. "main", "temp" or an attached database) via a single 
+          sqlite3* database handle.
+
+  </p></li><li> <p>The session object is configured with a set of tables to monitor
+          changes on.
+
+       </p><p> By default a session object does not monitor changes on any 
+           database table. Before it does so it must be configured. There 
+           are three ways to configure the set of tables to monitor changes
+           on:
+       </p><ul>
+         <li> By explicitly specifying tables using one call to
+              <a href="session/sqlite3session_attach.html">sqlite3session_attach()</a> for each table, or
+
+         </li><li> By specifying that all tables in the database should be monitored
+              for changes using a call to <a href="session/sqlite3session_attach.html">sqlite3session_attach()</a> with a
+              NULL argument, or
+
+         </li><li> By configuring a callback to be invoked the first time each table
+              is written to that indicates to the session module whether or
+              not changes on the table should be monitored.
+       </li></ul>
+        <p> The example code below uses the second of the methods enumerated
+            above - it monitors for changes on all database tables.
+
+  </p></li><li> <p> Changes are made to the database by executing SQL statements. The
+           session object records these changes.
+
+  </p></li><li> <p> A changeset blob is extracted from the session object using a call
+           to <a href="session/sqlite3session_changeset.html">sqlite3session_changeset()</a> (or, if using patchsets, a call to
+           the <a href="session/sqlite3session_patchset.html">sqlite3session_patchset()</a> function).
+
+  </p></li><li> <p> The session object is deleted using a call to the 
+           <a href="session/sqlite3session_delete.html">sqlite3session_delete()</a> API function.
+
+       </p><p> It is not necessary to delete a session object after extracting
+           a changeset or patchset from it. It can be left attached to the
+           database handle and will continue monitoring for changes on the
+           configured tables as before. However, if 
+           <a href="session/sqlite3session_changeset.html">sqlite3session_changeset()</a> or <a href="session/sqlite3session_patchset.html">sqlite3session_patchset()</a> is
+           called a second time on a session object, the changeset or patchset
+           will contain <em>all</em> changes that have taken place on the connection
+           since the session was created. In other words,
+           a session object is not reset or
+           zeroed by a call to sqlite3session_changeset() or
+           sqlite3session_patchset().
+</p></li></ol>
+
+<div class="codeblock"><pre><i>/*
+** Argument zSql points to a buffer containing an SQL script to execute 
+** against the database handle passed as the first argument. As well as
+** executing the SQL script, this function collects a changeset recording
+** all changes made to the "main" database file. Assuming no error occurs,
+** output variables (*ppChangeset) and (*pnChangeset) are set to point
+** to a buffer containing the changeset and the size of the changeset in
+** bytes before returning SQLITE_OK. In this case it is the responsibility
+** of the caller to eventually free the changeset blob by passing it to
+** the sqlite3_free function.
+**
+** Or, if an error does occur, return an SQLite error code. The final
+** value of (*pChangeset) and (*pnChangeset) are undefined in this case.
+*/</i>
+int sql_exec_changeset(
+  sqlite3 *db,                  <i>/* Database handle */</i>
+  const char *zSql,             <i>/* SQL script to execute */</i>
+  int *pnChangeset,             <i>/* OUT: Size of changeset blob in bytes */</i>
+  void **ppChangeset            <i>/* OUT: Pointer to changeset blob */</i>
+){
+  sqlite3_session *pSession = 0;
+  int rc;
+
+  <i>/* Create a new session object */</i>
+  rc = sqlite3session_create(db, "main", &pSession);
+
+  <i>/* Configure the session object to record changes to all tables */</i>
+  if( rc==SQLITE_OK ) rc = sqlite3session_attach(pSession, NULL);
+
+  <i>/* Execute the SQL script */</i>
+  if( rc==SQLITE_OK ) rc = sqlite3_exec(db, zSql, 0, 0, 0);
+
+  <i>/* Collect the changeset */</i>
+  if( rc==SQLITE_OK ){
+    rc = sqlite3session_changeset(pSession, pnChangeset, ppChangeset);
+  }
+
+  <i>/* Delete the session object */</i>
+  sqlite3session_delete(pSession);
+
+  return rc;
+}
+</pre></div>
+
+<h2 id="applying_a_changeset_to_a_database"><span>3.2. </span>Applying a Changeset to a Database</h2>
+
+<p> Applying a changeset to a database is simpler than capturing a changeset.
+Usually, a single call to <a href="session/sqlite3changeset_apply.html">sqlite3changeset_apply()</a>, as depicted in the
+example code below, suffices.
+
+</p><p> In cases where it is complicated, the complications in applying a 
+changeset lie in conflict resolution. Refer to the API documentation linked
+above for details.
+
+  </p><div class="codeblock"><pre><i>/*
+** Conflict handler callback used by apply_changeset(). See below.
+*/</i>
+static int xConflict(void *pCtx, int eConflict, sqlite3_changset_iter *pIter){
+  int ret = (int)pCtx;
+  return ret;
+}
+
+<i>/*
+** Apply the changeset contained in blob pChangeset, size nChangeset bytes,
+** to the main database of the database handle passed as the first argument.
+** Return SQLITE_OK if successful, or an SQLite error code if an error
+** occurs.
+**
+** If parameter bIgnoreConflicts is true, then any conflicting changes 
+** within the changeset are simply ignored. Or, if bIgnoreConflicts is
+** false, then this call fails with an SQLTIE_ABORT error if a changeset
+** conflict is encountered.
+*/</i>
+int apply_changeset(
+  sqlite3 *db,                  <i>/* Database handle */</i>
+  int bIgnoreConflicts,         <i>/* True to ignore conflicting changes */</i>
+  int nChangeset,               <i>/* Size of changeset in bytes */</i>
+  void *pChangeset              <i>/* Pointer to changeset blob */</i>
+){
+  return sqlite3changeset_apply(
+      db, 
+      nChangeset, pChangeset, 
+      0, xConflict, 
+      (void*)bIgnoreConflicts
+  );
+}
+</pre></div>
+
+<h2 id="inspecting_the_contents_of_a_changeset"><span>3.3. </span>Inspecting the Contents of a Changeset</h2>
+
+<p> The example code below demonstrates the techniques used to iterate 
+through and extract the data related to all changes in a changeset. To
+summarize:
+
+</p><ol>
+  <li><p> The <a href="session/sqlite3changeset_start.html">sqlite3changeset_start()</a> API is called to create and
+          initialize an iterator to iterate through the contents of a
+          changeset. Initially, the iterator points to no element at all.
+
+  </p></li><li><p> The first call to <a href="session/sqlite3changeset_next.html">sqlite3changeset_next()</a> on the iterator moves
+          it to point to the first change  in the changeset (or to EOF, if 
+          the changeset is completely empty). sqlite3changeset_next() returns
+          SQLITE_ROW if it moves the iterator to point to a valid entry,
+          SQLITE_DONE if it moves the iterator to EOF, or an SQLite error
+          code if an error occurs.
+
+  </p></li><li><p> If the iterator points to a valid entry, the <a href="session/sqlite3changeset_op.html">sqlite3changeset_op()</a>
+          API may be used to determine the type of change (INSERT, UPDATE or
+          DELETE) that the iterator points to. Additionally, the same API 
+          can be used to obtain the name of the table the change applies to
+          and its expected number of columns and primary key columns.
+
+  </p></li><li><p> If the iterator points to a valid INSERT or UPDATE entry, the
+          <a href="session/sqlite3changeset_new.html">sqlite3changeset_new()</a> API may be used to obtain the new.* values
+          within the change payload.
+
+  </p></li><li><p> If the iterator points to a valid DELETE or UPDATE entry, the
+          <a href="session/sqlite3changeset_old.html">sqlite3changeset_old()</a> API may be used to obtain the old.* values
+          within the change payload.
+
+  </p></li><li><p> An iterator is deleted using a call to the 
+          <a href="session/sqlite3changeset_finalize.html">sqlite3changeset_finalize()</a> API. If an error occured while
+          iterating, an SQLite error code is returned (even if the same error
+          code has already been returned by sqlite3changeset_next()). Or,
+          if no error has occurred, SQLITE_OK is returned.
+</p></li></ol>
+
+  <div class="codeblock"><pre><i>/*
+** Print the contents of the changeset to stdout.
+*/</i>
+static int print_changeset(void *pChangeset, int nChangeset){
+  int rc;
+  sqlite3_changeset_iter *pIter = 0;
+
+  <i>/* Create an iterator to iterate through the changeset */</i>
+  rc = sqlite3changeset_start(&pIter, nChangeset, pChangeset);
+  if( rc!=SQLITE_OK ) return rc;
+
+  <i>/* This loop runs once for each change in the changeset */</i>
+  while( SQLITE_ROW==sqlite3changeset_next(pIter) ){
+    const char *zTab;           <i>/* Table change applies to */</i>
+    int nCol;                   <i>/* Number of columns in table zTab */</i>
+    int op;                     <i>/* SQLITE_INSERT, UPDATE or DELETE */</i>
+    sqlite3_value *pVal;
+
+    <i>/* Print the type of operation and the table it is on */</i>
+    rc = sqlite3changeset_op(pIter, &zTab, &nCol, &op, 0);
+    if( rc!=SQLITE_OK ) goto exit_print_changeset;
+    printf("%s on table %s\n",
+      op==SQLITE_INSERT?"INSERT" : op==SQLITE_UPDATE?"UPDATE" : "DELETE",
+      zTab
+    );
+
+    <i>/* If this is an UPDATE or DELETE, print the old.* values */</i>
+    if( op==SQLITE_UPDATE || op==SQLITE_DELETE ){
+      printf("Old values:");
+      for(i=0; i&lt;nCol; i++){
+        rc = sqlite3changeset_old(pIter, i, &pVal);
+        if( rc!=SQLITE_OK ) goto exit_print_changeset;
+        printf(" %s", pVal ? sqlite3_value_text(pVal) : "-");
+      }
+      printf("\n");
+    }
+
+    <i>/* If this is an UPDATE or INSERT, print the new.* values */</i>
+    if( op==SQLITE_UPDATE || op==SQLITE_INSERT ){
+      printf("New values:");
+      for(i=0; i&lt;nCol; i++){
+        rc = sqlite3changeset_new(pIter, i, &pVal);
+        if( rc!=SQLITE_OK ) goto exit_print_changeset;
+        printf(" %s", pVal ? sqlite3_value_text(pVal) : "-");
+      }
+      printf("\n");
+    }
+  }
+
+  <i>/* Clean up the changeset and return an error code (or SQLITE_OK) */</i>
+ exit_print_changeset:
+  rc2 = sqlite3changeset_finalize(pIter);
+  if( rc==SQLITE_OK ) rc = rc2;
+  return rc;
+}
+</pre></div>
+
+<h1 id="extended_functionality"><span>4. </span>Extended Functionality</h1>
+
+<p> Most applications will only use the session module functionality described
+in the previous section. However, the following additional functionality is
+available for the use and manipulation of changeset and patchset blobs:
+
+</p><ul>
+  <li> <p>Two or more changeset/patchsets may be combined using the 
+       <a href="session/sqlite3changeset_concat.html">sqlite3changeset_concat()</a> or <a href="session/changegroup.html">sqlite3_changegroup</a> interfaces.
+
+  </p></li><li> <p>A changeset may be "inverted" using the <a href="session/sqlite3changeset_invert.html">sqlite3changeset_invert()</a>
+       API function. An inverted changeset undoes the changes made by the
+       original. If changeset C<sup>+</sup> is the inverse of changeset C, then
+       applying C and then C<sup>+</sup> to a database should leave
+       the database unchanged.
+</p></li></ul><p align="center"><small><i>This page last modified on  <a href="https://sqlite.org/docsrc/honeypot" id="mtimelink"  data-href="https://sqlite.org/docsrc/finfo/pages/sessionintro.in?m=007ada577d1408286">2018-02-28 22:21:53</a> UTC </small></i></p>
+
author	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-05-05 17:28:19 +0000
committer	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-05-05 17:28:19 +0000
commit	18657a960e125336f704ea058e25c27bd3900dcb (patch)
tree	17b438b680ed45a996d7b59951e6aa34023783f2 /www/sessionintro.html
parent	Initial commit. (diff)
download	sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.tar.xz sqlite3-18657a960e125336f704ea058e25c27bd3900dcb.zip