campo-sirio/libraries/SQLite3/sqlite-doc-3330000/c3ref/c_vtab_constraint_support.html
Alessandro Bonazzi 5c7aa8c1c0 Patch level : 12.0 no-patch
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Aggiunta documentazione di sqlite 3
2020-11-29 00:32:36 +01:00

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<title>Virtual Table Configuration Options</title>
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<!-- keywords: SQLITE_VTAB_CONSTRAINT_SUPPORT SQLITE_VTAB_DIRECTONLY SQLITE_VTAB_INNOCUOUS {virtual table configuration option} {virtual table configuration options} -->
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<a href="intro.html"><h2>SQLite C Interface</h2></a>
<h2>Virtual Table Configuration Options</h2>
</div>
<blockquote><pre>
#define SQLITE_VTAB_CONSTRAINT_SUPPORT 1
#define SQLITE_VTAB_INNOCUOUS 2
#define SQLITE_VTAB_DIRECTONLY 3
</pre></blockquote>
<p>
These macros define the various options to the
<a href="../c3ref/vtab_config.html">sqlite3_vtab_config()</a> interface that <a href="../vtab.html">virtual table</a> implementations
can use to customize and optimize their behavior.</p>
<p><dl>
<a name="sqlitevtabconstraintsupport"></a>
<dt>SQLITE_VTAB_CONSTRAINT_SUPPORT</dt>
<dd>Calls of the form
<a href="../c3ref/vtab_config.html">sqlite3_vtab_config</a>(db,SQLITE_VTAB_CONSTRAINT_SUPPORT,X) are supported,
where X is an integer. If X is zero, then the <a href="../vtab.html">virtual table</a> whose
<a href="../vtab.html#xcreate">xCreate</a> or <a href="../vtab.html#xconnect">xConnect</a> method invoked <a href="../c3ref/vtab_config.html">sqlite3_vtab_config()</a> does not
support constraints. In this configuration (which is the default) if
a call to the <a href="../vtab.html#xupdate">xUpdate</a> method returns <a href="../rescode.html#constraint">SQLITE_CONSTRAINT</a>, then the entire
statement is rolled back as if <a href="../lang_conflict.html">OR ABORT</a> had been
specified as part of the users SQL statement, regardless of the actual
ON CONFLICT mode specified.</p>
<p>If X is non-zero, then the virtual table implementation guarantees
that if <a href="../vtab.html#xupdate">xUpdate</a> returns <a href="../rescode.html#constraint">SQLITE_CONSTRAINT</a>, it will do so before
any modifications to internal or persistent data structures have been made.
If the <a href="../lang_conflict.html">ON CONFLICT</a> mode is ABORT, FAIL, IGNORE or ROLLBACK, SQLite
is able to roll back a statement or database transaction, and abandon
or continue processing the current SQL statement as appropriate.
If the ON CONFLICT mode is REPLACE and the <a href="../vtab.html#xupdate">xUpdate</a> method returns
<a href="../rescode.html#constraint">SQLITE_CONSTRAINT</a>, SQLite handles this as if the ON CONFLICT mode
had been ABORT.</p>
<p>Virtual table implementations that are required to handle OR REPLACE
must do so within the <a href="../vtab.html#xupdate">xUpdate</a> method. If a call to the
<a href="../c3ref/vtab_on_conflict.html">sqlite3_vtab_on_conflict()</a> function indicates that the current ON
CONFLICT policy is REPLACE, the virtual table implementation should
silently replace the appropriate rows within the xUpdate callback and
return SQLITE_OK. Or, if this is not possible, it may return
SQLITE_CONSTRAINT, in which case SQLite falls back to OR ABORT
constraint handling.
</dd></p>
<p><a name="sqlitevtabdirectonly"></a>
<dt>SQLITE_VTAB_DIRECTONLY</dt>
<dd>Calls of the form
<a href="../c3ref/vtab_config.html">sqlite3_vtab_config</a>(db,SQLITE_VTAB_DIRECTONLY) from within the
the <a href="../vtab.html#xconnect">xConnect</a> or <a href="../vtab.html#xcreate">xCreate</a> methods of a <a href="../vtab.html">virtual table</a> implmentation
prohibits that virtual table from being used from within triggers and
views.
</dd></p>
<p><a name="sqlitevtabinnocuous"></a>
<dt>SQLITE_VTAB_INNOCUOUS</dt>
<dd>Calls of the form
<a href="../c3ref/vtab_config.html">sqlite3_vtab_config</a>(db,SQLITE_VTAB_INNOCUOUS) from within the
the <a href="../vtab.html#xconnect">xConnect</a> or <a href="../vtab.html#xcreate">xCreate</a> methods of a <a href="../vtab.html">virtual table</a> implmentation
identify that virtual table as being safe to use from within triggers
and views. Conceptually, the SQLITE_VTAB_INNOCUOUS tag means that the
virtual table can do no serious harm even if it is controlled by a
malicious hacker. Developers should avoid setting the SQLITE_VTAB_INNOCUOUS
flag unless absolutely necessary.
</dd>
</dl>
</p><p>See also lists of
<a href="objlist.html">Objects</a>,
<a href="constlist.html">Constants</a>, and
<a href="funclist.html">Functions</a>.</p>