PostgreSQL Programmer's Guide
Prev | Chapter 14. Triggers | Next

# Interaction with the Trigger Manager

As mentioned above, when function is called by the trigger manager, structure TriggerData *CurrentTriggerData is NOT NULL and initialized. So it is better to check CurrentTriggerData against being NULL at the start and set it to NULL just after fetching the information to prevent calls to a trigger function not from the trigger manager.

struct TriggerData is defined in src/include/commands/trigger.h:

    typedef struct TriggerData
    {
        TriggerEvent  tg_event;
        Relation      tg_relation;
        HeapTuple     tg_trigtuple;
        HeapTuple     tg_newtuple;
        Trigger      *tg_trigger;
    } TriggerData;

where the members are defined as follows:

tg_event

  describes the event for which the function is called. You may use the following macros to examine `tg_event`:

  TRIGGER_FIRED_BEFORE(tg_event)

    returns TRUE if trigger fired BEFORE.

  TRIGGER_FIRED_AFTER(tg_event)

    Returns TRUE if trigger fired AFTER.

  TRIGGER_FIRED_FOR_ROW(event)

    Returns TRUE if trigger fired for a ROW-level event.

  TRIGGER_FIRED_FOR_STATEMENT(event)

    Returns TRUE if trigger fired for STATEMENT-level event.

  TRIGGER_FIRED_BY_INSERT(event)

    Returns TRUE if trigger fired by INSERT.

  TRIGGER_FIRED_BY_DELETE(event)

    Returns TRUE if trigger fired by DELETE.

  TRIGGER_FIRED_BY_UPDATE(event)

    Returns TRUE if trigger fired by UPDATE.

tg_relation

  is a pointer to structure describing the triggered relation. Look at src/include/utils/rel.h for details about this structure. The most interest things are tg_relation->rd_att (descriptor of the relation tuples) and tg_relation->rd_rel->relname (relation's name. This is not char*, but NameData. Use SPI_getrelname(tg_relation) to get char* if you need a copy of name).

tg_trigtuple

  is a pointer to the tuple for which the trigger is fired. This is the tuple being inserted (if INSERT), deleted (if DELETE) or updated (if UPDATE). If INSERT/DELETE then this is what you are to return to Executor if you don't want to replace tuple with another one (INSERT) or skip the operation.

tg_newtuple

  is a pointer to the new version of tuple if UPDATE and NULL if this is for an INSERT or a DELETE. This is what you are to return to Executor if UPDATE and you don't want to replace this tuple with another one or skip the operation.

tg_trigger

  is pointer to structure Trigger defined in src/include/utils/rel.h:

      typedef struct Trigger
      {
          Oid         tgoid;
          char       *tgname;
          Oid         tgfoid;
          FmgrInfo    tgfunc;
          int16       tgtype;
          bool        tgenabled;
          bool        tgisconstraint;
          bool        tgdeferrable;
          bool        tginitdeferred;
          int16       tgnargs;
          int16       tgattr[FUNC_MAX_ARGS];
          char      **tgargs;
      } Trigger;

  where tgname is the trigger's name, tgnargs is number of arguments in tgargs, tgargs is an array of pointers to the arguments specified in the CREATE TRIGGER statement. Other members are for internal use only.

Prev | Home | Next
Triggers | Up | Visibility of Data Changes