PostgreSQL Trigger to override insert on table with inheritance

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Question :

We have a table documents that is partitioned by time into child tables like documents_2019_01, documents_2019_02. We do this using a BEFORE trigger on the parent documents table to insert into the correct child table and then return NULL to abort the pipeline so it is only inserted into the child table, though (you guessed it), this makes inserting documents a pain as you have to re-query for the created ids. We’ve looked into using an INSTEAD OF trigger type, but they cannot be applied to tables, only views.

Here is our current function used by the trigger:

CREATE OR REPLACE FUNCTION create_article_partition_and_insert() RETURNS TRIGGER
    LANGUAGE plpgsql
    partition_date TEXT;
    partition      TEXT;
    resultId       BIGINT;
    partition_date := to_char(NEW.updated, 'YYYY_MM');
    partition := TG_RELNAME || '_' || partition_date;
    IF NOT EXISTS(SELECT relname FROM pg_class WHERE relname = partition)
        RAISE NOTICE 'A partition has been created %',partition;
        EXECUTE 'CREATE TABLE ' || partition || ' (LIKE ' || TG_RELNAME || ' INCLUDING ALL) INHERITS (' || TG_RELNAME ||
                '); ';
    END IF;
    RAISE NOTICE 'Inserting into %',partition;
    EXECUTE 'INSERT INTO ' || partition || ' SELECT(' || TG_RELNAME || ' ' || quote_literal(NEW) || ').* RETURNING id;'
        INTO resultId; := resultId;

Is there a better way to partition inserts by time and return the inserted row of the child table without also inserting into the parent table?

Using PG version 9.6.11.

Thank you!

Cross-posting from SO

Answer :

You could possibly use lastval() or currval() to get the last value from the sequence. or use nextval() to get the id before the insert and then insert that value explicitly (instead of allowing the default value).

The third option is to ignore that column and instead use a natural key. That you are able to get the ID by doing a select suggests that there is a natural key for this table.

Lastval and currval are private to your connection, so must be issued on the same connection that issued the insert.

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