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F.61.1. refint — Functions for Implementing Referential Integrity

F.61.2. autoinc — Functions for Autoincrementing Fields

F.61.3. insert_username — Functions for Tracking Who Changed a Table

F.61.4. moddatetime — Functions for Tracking Last Modification Time

check_primary_key() andcheck_foreign_key() are used to check foreign key constraints. (This functionality is long since superseded by the built-in foreign key mechanism, of course, but the module is still useful as an example.)

check_primary_key() checks the referencing table. To use, create aBEFORE INSERT OR UPDATE trigger using this function on a table referencing another table. Specify as the trigger arguments: the referencing table's column name(s) which form the foreign key, the referenced table name, and the column names in the referenced table which form the primary/unique key. To handle multiple foreign keys, create a trigger for each reference.

check_foreign_key() checks the referenced table. To use, create aBEFORE DELETE OR UPDATE trigger using this function on a table referenced by other table(s). Specify as the trigger arguments: the number of referencing tables for which the function has to perform checking, the action if a referencing key is found (cascade — to delete the referencing row,restrict — to abort transaction if referencing keys exist,setnull — to set referencing key fields to null), the triggered table's column names which form the primary/unique key, then the referencing table name and column names (repeated for as many referencing tables as were specified by first argument). Note that the primary/unique key columns should be marked NOT NULL and should have a unique index.

There are examples inrefint.example.

autoinc() is a trigger that stores the next value of a sequence into an integer field. This has some overlap with the built-in“serial column” feature, but it is not the same:autoinc() will override attempts to substitute a different field value during inserts, and optionally it can be used to increment the field during updates, too.

To use, create aBEFORE INSERT (or optionallyBEFORE INSERT OR UPDATE) trigger using this function. Specify two trigger arguments: the name of the integer column to be modified, and the name of the sequence object that will supply values. (Actually, you can specify any number of pairs of such names, if you'd like to update more than one autoincrementing column.)

There is an example inautoinc.example.

insert_username() is a trigger that stores the current user's name into a text field. This can be useful for tracking who last modified a particular row within a table.

To use, create aBEFORE INSERT and/orUPDATE trigger using this function. Specify a single trigger argument: the name of the text column to be modified.

There is an example ininsert_username.example.

moddatetime() is a trigger that stores the current time into atimestamp field. This can be useful for tracking the last modification time of a particular row within a table.

To use, create aBEFORE UPDATE trigger using this function. Specify a single trigger argument: the name of the column to be modified. The column must be of typetimestamp ortimestamp with time zone.

There is an example inmoddatetime.example.