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105 lines
4.0 KiB
Plaintext
105 lines
4.0 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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2. timetravel.c - functions for implementing time travel feature.
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Old internally supported time-travel (TT) used insert/delete
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transaction commit times. To get the same feature using triggers
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you are to add to a table two columns of abstime type to store
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date when a tuple was inserted (start_date) and changed/deleted
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(stop_date):
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CREATE TABLE XXX (
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... ...
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date_on abstime default currabstime(),
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date_off abstime default 'infinity'
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... ...
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);
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- so, tuples being inserted with NULLs in date_on/date_off will get
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_current_date_ in date_on (name of start_date column in XXX) and INFINITY in
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date_off (name of stop_date column in XXX).
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Tuples with stop_date equal INFINITY are "valid now": when trigger will
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be fired for UPDATE/DELETE of a tuple with stop_date NOT equal INFINITY then
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this tuple will not be changed/deleted!
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If stop_date equal INFINITY then on
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UPDATE: only stop_date in tuple being updated will be changed to current
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date and new tuple with new data (coming from SET ... in UPDATE) will be
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inserted. Start_date in this new tuple will be setted to current date and
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stop_date - to INFINITY.
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DELETE: new tuple will be inserted with stop_date setted to current date
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(and with the same data in other columns as in tuple being deleted).
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NOTE:
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1. To get tuples "valid now" you are to add _stop_date_ = 'infinity'
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to WHERE. Internally supported TT allowed to avoid this...
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Fixed rewriting RULEs could help here...
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As work arround you may use VIEWs...
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2. You can't change start/stop date columns with UPDATE!
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Use set_timetravel (below) if you need in this.
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FUNCTIONs:
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timetravel() is general trigger function.
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You are to create trigger BEFORE (!!!) UPDATE OR DELETE using this
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function on a time-traveled table. You are to specify two arguments: name of
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start_date column and name of stop_date column in triggered table.
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currabstime() may be used in DEFAULT for start_date column to get
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current date.
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set_timetravel() allows you turn time-travel ON/OFF for a table:
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set_timetravel('XXX', 1) will turn TT ON for table XXX (and report
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old status).
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set_timetravel('XXX', 0) will turn TT OFF for table XXX (-"-).
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Turning TT OFF allows you do with a table ALL what you want.
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There is example in timetravel.example.
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To CREATE FUNCTIONs use timetravel.sql (will be made by gmake from
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timetravel.source).
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