203 lines
9.4 KiB
HTML
203 lines
9.4 KiB
HTML
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<!-- keywords: sqlite3_preupdate_count sqlite3_preupdate_depth sqlite3_preupdate_hook sqlite3_preupdate_new sqlite3_preupdate_old -->
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<div class=nosearch>
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<a href="intro.html"><h2>SQLite C Interface</h2></a>
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<h2>The pre-update hook.</h2>
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</div>
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<blockquote><pre>
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#if defined(SQLITE_ENABLE_PREUPDATE_HOOK)
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void *sqlite3_preupdate_hook(
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sqlite3 *db,
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void(*xPreUpdate)(
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void *pCtx, /* Copy of third arg to preupdate_hook() */
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sqlite3 *db, /* Database handle */
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int op, /* SQLITE_UPDATE, DELETE or INSERT */
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char const *zDb, /* Database name */
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char const *zName, /* Table name */
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sqlite3_int64 iKey1, /* Rowid of row about to be deleted/updated */
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sqlite3_int64 iKey2 /* New rowid value (for a rowid UPDATE) */
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),
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void*
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);
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int sqlite3_preupdate_old(sqlite3 *, int, sqlite3_value **);
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int sqlite3_preupdate_count(sqlite3 *);
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int sqlite3_preupdate_depth(sqlite3 *);
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int sqlite3_preupdate_new(sqlite3 *, int, sqlite3_value **);
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#endif
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</pre></blockquote>
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<p>
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These interfaces are only available if SQLite is compiled using the
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<a href="../compile.html#enable_preupdate_hook">SQLITE_ENABLE_PREUPDATE_HOOK</a> compile-time option.</p>
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<p>The <a href="../c3ref/preupdate_count.html">sqlite3_preupdate_hook()</a> interface registers a callback function
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that is invoked prior to each <a href="../lang_insert.html">INSERT</a>, <a href="../lang_update.html">UPDATE</a>, and <a href="../lang_delete.html">DELETE</a> operation
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on a database table.
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At most one preupdate hook may be registered at a time on a single
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<a href="../c3ref/sqlite3.html">database connection</a>; each call to <a href="../c3ref/preupdate_count.html">sqlite3_preupdate_hook()</a> overrides
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the previous setting.
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The preupdate hook is disabled by invoking <a href="../c3ref/preupdate_count.html">sqlite3_preupdate_hook()</a>
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with a NULL pointer as the second parameter.
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The third parameter to <a href="../c3ref/preupdate_count.html">sqlite3_preupdate_hook()</a> is passed through as
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the first parameter to callbacks.</p>
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<p>The preupdate hook only fires for changes to real database tables; the
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preupdate hook is not invoked for changes to <a href="../vtab.html">virtual tables</a> or to
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system tables like sqlite_sequence or sqlite_stat1.</p>
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<p>The second parameter to the preupdate callback is a pointer to
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the <a href="../c3ref/sqlite3.html">database connection</a> that registered the preupdate hook.
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The third parameter to the preupdate callback is one of the constants
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<a href="../c3ref/c_alter_table.html">SQLITE_INSERT</a>, <a href="../c3ref/c_alter_table.html">SQLITE_DELETE</a>, or <a href="../c3ref/c_alter_table.html">SQLITE_UPDATE</a> to identify the
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kind of update operation that is about to occur.
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The fourth parameter to the preupdate callback is the name of the
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database within the database connection that is being modified. This
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will be "main" for the main database or "temp" for TEMP tables or
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the name given after the AS keyword in the <a href="../lang_attach.html">ATTACH</a> statement for attached
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databases.
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The fifth parameter to the preupdate callback is the name of the
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table that is being modified.</p>
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<p>For an UPDATE or DELETE operation on a <a href="../rowidtable.html">rowid table</a>, the sixth
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parameter passed to the preupdate callback is the initial <a href="../lang_createtable.html#rowid">rowid</a> of the
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row being modified or deleted. For an INSERT operation on a rowid table,
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or any operation on a WITHOUT ROWID table, the value of the sixth
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parameter is undefined. For an INSERT or UPDATE on a rowid table the
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seventh parameter is the final rowid value of the row being inserted
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or updated. The value of the seventh parameter passed to the callback
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function is not defined for operations on WITHOUT ROWID tables, or for
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INSERT operations on rowid tables.</p>
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<p>The <a href="../c3ref/preupdate_count.html">sqlite3_preupdate_old()</a>, <a href="../c3ref/preupdate_count.html">sqlite3_preupdate_new()</a>,
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<a href="../c3ref/preupdate_count.html">sqlite3_preupdate_count()</a>, and <a href="../c3ref/preupdate_count.html">sqlite3_preupdate_depth()</a> interfaces
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provide additional information about a preupdate event. These routines
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may only be called from within a preupdate callback. Invoking any of
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these routines from outside of a preupdate callback or with a
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<a href="../c3ref/sqlite3.html">database connection</a> pointer that is different from the one supplied
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to the preupdate callback results in undefined and probably undesirable
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behavior.</p>
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<p>The <a href="../c3ref/preupdate_count.html">sqlite3_preupdate_count(D)</a> interface returns the number of columns
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in the row that is being inserted, updated, or deleted.</p>
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<p>The <a href="../c3ref/preupdate_count.html">sqlite3_preupdate_old(D,N,P)</a> interface writes into P a pointer to
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a <a href="../c3ref/value.html">protected sqlite3_value</a> that contains the value of the Nth column of
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the table row before it is updated. The N parameter must be between 0
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and one less than the number of columns or the behavior will be
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undefined. This must only be used within SQLITE_UPDATE and SQLITE_DELETE
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preupdate callbacks; if it is used by an SQLITE_INSERT callback then the
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behavior is undefined. The <a href="../c3ref/value.html">sqlite3_value</a> that P points to
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will be destroyed when the preupdate callback returns.</p>
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<p>The <a href="../c3ref/preupdate_count.html">sqlite3_preupdate_new(D,N,P)</a> interface writes into P a pointer to
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a <a href="../c3ref/value.html">protected sqlite3_value</a> that contains the value of the Nth column of
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the table row after it is updated. The N parameter must be between 0
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and one less than the number of columns or the behavior will be
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undefined. This must only be used within SQLITE_INSERT and SQLITE_UPDATE
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preupdate callbacks; if it is used by an SQLITE_DELETE callback then the
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behavior is undefined. The <a href="../c3ref/value.html">sqlite3_value</a> that P points to
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will be destroyed when the preupdate callback returns.</p>
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<p>The <a href="../c3ref/preupdate_count.html">sqlite3_preupdate_depth(D)</a> interface returns 0 if the preupdate
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callback was invoked as a result of a direct insert, update, or delete
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operation; or 1 for inserts, updates, or deletes invoked by top-level
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triggers; or 2 for changes resulting from triggers called by top-level
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triggers; and so forth.</p>
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<p>See also: <a href="../c3ref/update_hook.html">sqlite3_update_hook()</a>
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</p><p>See also lists of
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<a href="objlist.html">Objects</a>,
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<a href="constlist.html">Constants</a>, and
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<a href="funclist.html">Functions</a>.</p>
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