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POHow to write a delete rule on a view?
 

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  1. POHow to write a delete rule on a view?
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    <p>I'm trying to write a rule on a view to delete tuples from the component tables, but so far can only remove data from one of them. I've used postgres with basic views for a while, but I don't have any experience with rules on views.</p> <p>I wrote a stupid little test case to figure out/show my problem. There's only one parent tuple per child tuple in this example (my actual schema isn't actually like this of course).</p> <p><strong>Component tables:</strong></p> <pre><code>CREATE TABLE parent( id serial PRIMARY KEY, p_data integer NOT NULL UNIQUE ); CREATE TABLE child( id serial PRIMARY KEY, parent_id integer NOT NULL UNIQUE REFERENCES parent(id), c_data integer NOT NULL ); </code></pre> <p><strong>View:</strong></p> <pre><code>CREATE TABLE child_view( id integer, p_data integer, c_data integer ); CREATE RULE "_RETURN" AS ON SELECT TO child_view DO INSTEAD SELECT child.id, p_data, c_data FROM parent JOIN child ON (parent_id=parent.id); </code></pre> <p><strong>Problem delete rule</strong></p> <pre><code>CREATE RULE child_delete AS ON DELETE TO child_view DO INSTEAD( DELETE FROM child WHERE id=OLD.id; DELETE FROM parent WHERE p_data=OLD.p_data; ); </code></pre> <p>The intent of the above rule is to remove tuples referenced in the view from the component tables. The <code>WHERE p_data=OLD.p_data</code> seems odd to me, but I don't see how else to reference the desired tuple in the parent table.</p> <p>Here's what happens when I try to use the above rule:</p> <pre><code>&gt;SELECT * FROM child_view; id | p_data | c_data ----+--------+-------- 1 | 1 | 10 2 | 2 | 11 3 | 3 | 12 (3 rows) &gt;DELETE FROM child_view WHERE id=3; DELETE 0 &gt;SELECT * FROM child_view; id | p_data | c_data ----+--------+-------- 1 | 1 | 10 2 | 2 | 11 (2 rows) </code></pre> <p>But looking at the parent table, the second part of the delete isn't working (id=3 "should" have been deleted):</p> <pre><code>&gt;SELECT * FROM parent; id | p_data ----+-------- 1 | 1 2 | 2 3 | 3 (3 rows) </code></pre> <p>How should I write the deletion rule to remove both child and parent tuples?</p> <p>This is using postgres v9. </p> <p>Any help is appreciated. Also pointers to any materials covering rules on views beyond the postgres docs (unless I've obviously missed something) would also be appreciated. Thanks.</p> <p>EDIT: as jmz points out, it would be easier to use a cascading delete than a rule here, but that approach doesn't work for my actual schema.</p>
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