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;

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

   TRIGGER_FIRED_BEFORE(event) returns TRUE if trigger fired BEFORE;
   TRIGGER_FIRED_AFTER(event) returns TRUE if trigger fired AFTER;
   TRIGGER_FIRED_FOR_ROW(event) returns TRUE if trigger fired for
                                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 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
{
        char            *tgname;
        Oid             tgfoid;
        func_ptr        tgfunc;
        int16           tgtype;
        int16           tgnargs;
        int16           tgattr[8];
        char            **tgargs;
} Trigger;

   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.