110 lines
3.9 KiB
Plaintext
110 lines
3.9 KiB
Plaintext
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Here are general trigger functions provided as workable examples
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of using SPI and triggers. "General" means that functions may be
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used for defining triggers for any tables but you have to specify
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table/field names (as described below) while creating a trigger.
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1. refint.c - functions for implementing referential integrity.
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check_primary_key () is to used for foreign keys of a table.
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You are to create trigger (BEFORE INSERT OR UPDATE) using this
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function on a table referencing another table. You are to specify
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as function arguments: triggered table column names which correspond
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to foreign key, referenced table name and column names in referenced
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table which correspond to primary/unique key.
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You may create as many triggers as you need - one trigger for
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one reference.
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check_foreign_key () is to used for primary/unique keys of a table.
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You are to create trigger (BEFORE DELETE OR UPDATE) using this
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function on a table referenced by another table(s). You are to specify
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as function arguments: number of references for which function has to
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performe checking, action if referencing key found ('cascade' - to delete
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corresponding foreign key, 'restrict' - to abort transaction if foreign keys
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exist, 'setnull' - to set foreign key referencing primary/unique key
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being deleted to null), triggered table column names which correspond
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to primary/unique key, referencing table name and column names corresponding
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to foreign key (, ... - as many referencing tables/keys as specified
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by first argument).
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Note, that NOT NULL constraint and unique index have to be defined by
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youself.
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There are examples in refint.example and regression tests
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(sql/triggers.sql).
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To CREATE FUNCTIONs use refint.sql (will be made by gmake from
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refint.source).
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# Excuse me for my bad english. Massimo Lambertini
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#
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#
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# New check foreign key
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#
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I think that cascade mode is to be considered like that the operation over
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main table is to be made also in referenced table .
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When i Delete , i must delete from referenced table ,
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but when i update , i update referenced table and not delete like unmodified refint.c .
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I made a new version of refint.c that when i update it check the type of modified key ( if is a text , char() i
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added '') and then create a update query that do the right thing .
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For my point of view that policy is helpfull because i do not have in referenced table
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loss of information .
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In preprocessor subdir i have placed a little utility that from a SQL92 table definition,
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it create all trigger for foreign key .
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the schema that i use to analyze the problem is this
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create table
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A
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( key int4 not null primary key ,...,
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) ;
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create table
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REFERENCED_B
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( key int 4 , ... ,
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foreign key ( key ) references A --
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);
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--
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-- Trigger for REFERENCED_B
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--
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CREATE INDEX I_REFERENCED_B_KEY ON REFERENCED_B ( KEY ) ;
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CREATE TRIGGER T_P_REFERENCED_B_A BEFORE INSERT OR UPDATE ON REFERENCED_B FOR EACH ROW
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EXECUTE PROCEDURE
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check_primary_key('KEY','A','KEY' );
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CREATE TRIGGER T_F_D_A_REFERENCED_B BEFORE DELETE ON A FOR EACH ROW
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EXECUTE PROCEDURE
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check_foreign_key(1,'cascade','KEY','REFERENCED_B ','KEY' );
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CREATE TRIGGER T_F_U_A_REFERENCED_B AFTER UPDATE ON A FOR EACH ROW
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EXECUTE PROCEDURE
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check_foreign_key(1,'cascade','KEY','REFERENCED_B ','KEY' );
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-- ********************************
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I write TRIGGER T_F_U_A_REFERENCED_B ( AFTER ) and not BEFORE because if i set
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BEFORE , when i try to modify ( update ) a key of A , i start a execution of TRIGGER T_P_REFERENCED_B_A
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( check_primary_key) before the real modification of key in A , then the execution of ( check_primary_key) return
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not ok.
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With AFTER Clausole i modify first key of A then a update the value of referenced table REFERENCED_B.
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Try also the new_example.sql to view the modified policy.
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I wish that my explain of problem is quite clear .
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If there is miss understanding ( cause my bad english ) please send email to massimo.lambertini@everex.it
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