From 4a3bf197eb3ca020bc0eb0d5bc5d3838fd1e6851 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 6 Nov 2001 23:54:32 +0000
Subject: [PATCH] Add some notes about conditional rules used with views.
---
doc/src/sgml/ref/create_rule.sgml | 46 +++++++++++++++++++++++++++----
doc/src/sgml/ref/create_view.sgml | 10 +++++--
2 files changed, 47 insertions(+), 9 deletions(-)
diff --git a/doc/src/sgml/ref/create_rule.sgml b/doc/src/sgml/ref/create_rule.sgml
index 3d7e53ea527..ee17fbdded1 100644
--- a/doc/src/sgml/ref/create_rule.sgml
+++ b/doc/src/sgml/ref/create_rule.sgml
@@ -1,5 +1,5 @@
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_rule.sgml,v 1.28 2001/10/09 18:46:00 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_rule.sgml,v 1.29 2001/11/06 23:54:32 tgl Exp $
Postgres documentation
-->
@@ -196,10 +196,10 @@ CREATE
<refsect2 id="R2-SQL-CREATERULE-3">
<refsect2info>
- <date>2001-01-05</date>
+ <date>2001-11-06</date>
</refsect2info>
<title>
- Notes
+ Rules and Views
</title>
<para>
Presently, ON SELECT rules must be unconditional INSTEAD rules and must
@@ -207,10 +207,44 @@ CREATE
rule effectively turns the object table into a view, whose visible
contents are the rows returned by the rule's SELECT query rather than
whatever had been stored in the table (if anything). It is considered
- better style to write a CREATE VIEW command than to create a table and
- define an ON SELECT rule for it.
+ better style to write a CREATE VIEW command than to create a real table
+ and define an ON SELECT rule for it.
+ </para>
+
+ <para>
+ <xref linkend="sql-createview"> creates a dummy table (with no underlying
+ storage) and associates an ON SELECT rule with it. The system will not
+ allow updates to the view, since it knows there is no real table there.
+ You can create the
+ illusion of an updatable view by defining ON INSERT, ON UPDATE, and
+ ON DELETE rules (or any subset of those that's sufficient
+ for your purposes) to replace update actions on the view with
+ appropriate updates on other tables.
</para>
+ <para>
+ There is a catch if you try to use conditional
+ rules for view updates: there <emphasis>must</> be an unconditional
+ INSTEAD rule for each action you wish to allow on the view. If the
+ rule is conditional, or is not INSTEAD, then the system will still reject
+ attempts to perform the update action, because it thinks it might end up
+ trying to perform the action on the dummy table in some cases.
+ If you want to
+ handle all the useful cases in conditional rules, you can; just add an
+ unconditional DO INSTEAD NOTHING rule to ensure that the system
+ understands it will never be called on to update the dummy table. Then
+ make the conditional rules non-INSTEAD; in the cases where they fire,
+ they add to the default INSTEAD NOTHING action.
+ </para>
+ </refsect2>
+
+ <refsect2 id="R2-SQL-CREATERULE-4">
+ <refsect2info>
+ <date>2001-01-05</date>
+ </refsect2info>
+ <title>
+ Notes
+ </title>
<para>
You must have rule definition access to a table in order
to define a rule on it. Use <command>GRANT</command>
@@ -267,7 +301,7 @@ UPDATE mytable SET name = 'foo' WHERE id = 42;
Compatibility
</title>
- <refsect2 id="R2-SQL-CREATERULE-4">
+ <refsect2 id="R2-SQL-CREATERULE-5">
<refsect2info>
<date>1998-09-11</date>
</refsect2info>
diff --git a/doc/src/sgml/ref/create_view.sgml b/doc/src/sgml/ref/create_view.sgml
index bb383e41e5e..cc533e1824f 100644
--- a/doc/src/sgml/ref/create_view.sgml
+++ b/doc/src/sgml/ref/create_view.sgml
@@ -1,5 +1,5 @@
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_view.sgml,v 1.12 2001/09/03 12:57:49 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_view.sgml,v 1.13 2001/11/06 23:54:32 tgl Exp $
Postgres documentation
-->
@@ -102,7 +102,7 @@ ERROR: Relation '<replaceable class="parameter">view</replaceable>' already exi
</varlistentry>
<varlistentry>
<term><computeroutput>
-NOTICE create: attribute named "<replaceable class="parameter">column</replaceable>" has an unknown type
+NOTICE: Attribute '<replaceable class="parameter">column</replaceable>' has an unknown type
</computeroutput></term>
<listitem>
<para>
@@ -149,7 +149,11 @@ CREATE VIEW vista AS SELECT text 'Hello World'
</title>
<para>
- Currently, views are read only.
+ Currently, views are read only: the system will not allow an insert,
+ update, or delete on a view. You can get the effect of an updatable
+ view by creating rules that rewrite inserts, etc. on the view into
+ appropriate actions on other tables. For more information see
+ <xref linkend="sql-createrule">.
</para>
<para>
--
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