SELECT 级联 AFTER DELETE 触发器在 Postgres 11 中返回陈旧数据

Question

I have an AFTER INSERT/UPDATE/DELETE trigger function which runs after any change to table campaigns and triggers an update on table contracts :

CREATE OR REPLACE FUNCTION update_campaign_target() RETURNS trigger AS $update_campaign_target$
    BEGIN
        UPDATE contracts SET updated_at = now() WHERE contracts.contract_id = NEW.contract_id;
    END;
$update_campaign_target$ LANGUAGE plpgsql;

DROP TRIGGER IF EXISTS update_campaign_target ON campaigns;
CREATE TRIGGER update_campaign_target AFTER INSERT OR UPDATE OR DELETE ON campaigns
    FOR EACH ROW EXECUTE PROCEDURE update_campaign_target();

I have another trigger on table contracts that runs BEFORE UPDATE . The goal is to generate a computed column target which displays either contracts.manual_target (if set) or SUM(campaigns.target) WHERE campaign.contract_id = NEW.contract_id .

CREATE OR REPLACE FUNCTION update_contract_manual_target() RETURNS trigger AS $update_contract_manual_target$
    DECLARE
        campaign_target_count int;
    BEGIN
        IF NEW.manual_target IS NOT NULL
        THEN
            NEW.target := NEW.manual_target;
            RETURN NEW;
        ELSE
            SELECT SUM(campaigns.target) INTO campaign_target_count
                FROM campaigns
                WHERE campaigns.contract_id = NEW.contract_id;
            NEW.target := campaign_target_count;
            RETURN NEW;
        END IF;
    END;
$update_contract_manual_target$ LANGUAGE plpgsql;

DROP TRIGGER IF EXISTS update_contract_manual_target ON contracts;
CREATE TRIGGER update_contract_manual_target BEFORE INSERT OR UPDATE ON contracts
    FOR EACH ROW EXECUTE PROCEDURE update_contract_manual_target();

This works as expected on INSERT and UPDATE on campaigns , but does not work on DELETE. When a campaign is deleted, the result of SUM(campaigns.target) in the second trigger includes the deleted campaign's target, and thus does not update the contracts.target column to the expected value. A second update of contracts will correctly set the value.

Three questions:

1. Why doesn't this work?
2. Is there a way to achieve the behavior I'm looking for using triggers?
3. For this type of data synchronization, is it better to achieve this using triggers or views? Triggers make sense to me because this is a table that we will read many magnitudes of times more than we'll write to it, but I'm not sure what the best practices are.

Answer 1

The reason this doesn't work is the usage of NEW.contract_id in the AFTER DELETE trigger:

UPDATE contracts SET updated_at = now() WHERE contracts.contract_id = NEW.contract_id;

Per the Triggers on Data Changes documentation, NEW is NULL for DELETE triggers.

Updating the code to use OLD instead of NEW fixes the issue:

CREATE OR REPLACE FUNCTION update_campaign_target() RETURNS trigger AS $update_campaign_target$
    BEGIN
        IF TG_OP = 'DELETE'
        THEN
            UPDATE contracts SET updated_at = now() WHERE contracts.contract_id = OLD.contract_id;
        ELSE
            UPDATE contracts SET updated_at = now() WHERE contracts.contract_id = NEW.contract_id;
        END IF;
        RETURN NULL;
    END;
$update_campaign_target$ LANGUAGE plpgsql;

Thanks to Anthony Sotolongo and Belayer for your help!