Postgresql aggregate related values using triggers - postgresql

Question

I have a database representing a payroll system.
Each Payroll is related to several PayrollRows (1 to M relationship), and includes a field summarizing its related payrollRows fields.
Simply said, Payroll includes a field called "amountEurToPay" which is the sum of the "paybackEur" fields of its related PayrollRow records.
I am trying to create a trigger function that automatically completes the amountEurToPay field when a Payroll is created. (indeed it will be created directly with its payrollRow)
I have done this :
-- Generate the trigger function
CREATE OR REPLACE TRIGGER new_payroll_creation
AFTER INSERT
ON "Payroll"
FOR EACH ROW
EXECUTE PROCEDURE populate_payroll_amountEur();
For the function, I tried this, but without any success.
CREATE OR REPLACE FUNCTION populate_payroll_amounteur()
RETURNS TRIGGER
LANGUAGE PLPGSQL
AS
$$
BEGIN
UPDATE "Payroll"
SET "amountEurToPay" = ( SELECT SUM("paybackEur")
FROM "PayrollRow"
WHERE "payrollId" = NEW."id")
WHERE ("id" = NEW."id");
RETURN NEW;
END;
$$
For extra information, my schema looks like this
model PayrollRow {
id Int #id #default(autoincrement())
createdAt DateTime #default(now())
updatedAt DateTime #updatedAt
paybackEur Decimal #default(0) #db.Decimal(10, 2)
payroll Payroll #relation(fields: [payrollId], references: [id])
payrollId Int
}
model Payroll {
id Int #id #default(autoincrement())
createdAt DateTime #default(now())
updatedAt DateTime #updatedAt
amountEurToPay Decimal #default(0) #db.Decimal(10, 2)
payrollRow PayrollRow[]
}
Could you please provide me some support to achieve that? :)
UPDATE--
It seems that that this works (with a preexisting payroll with id 2) for example, I am a bit confused :
CREATE OR REPLACE FUNCTION populate_payroll_amounteur()
RETURNS TRIGGER
LANGUAGE PLPGSQL
AS
$$
BEGIN
UPDATE "Payroll"
SET "amountEurToPay" = ( SELECT SUM("paybackEur")
FROM "PayrollRow"
WHERE "payrollId" = 2)
WHERE ("id" = NEW."id");
RETURN NEW;
END;
$$
---- UPDATE for MiTKo
If you request the schema definition , actually I use prisma.io ORM , which simplified for me the creation of the schema.
Some reverse engineering would give something like this :
-- CreateTable
CREATE TABLE "Payroll" (
"id" SERIAL NOT NULL,
"createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
"updatedAt" TIMESTAMP(3) NOT NULL,
"amountEurToPay" DECIMAL(10,2) NOT NULL DEFAULT 0,
CONSTRAINT "Payroll_pkey" PRIMARY KEY ("id")
);
-- CreateTable
CREATE TABLE "PayrollRow" (
"id" SERIAL NOT NULL,
"createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
"updatedAt" TIMESTAMP(3) NOT NULL,
"paybackEur" DECIMAL(10,2) NOT NULL DEFAULT 0,
"payrollId" INTEGER NOT NULL,
CONSTRAINT "PayrollRow_pkey" PRIMARY KEY ("id")
);
-- AddForeignKey
ALTER TABLE "PayrollRow" ADD CONSTRAINT "PayrollRow_payrollId_fkey" FOREIGN KEY ("payrollId") REFERENCES "Payroll"("id") ON DELETE RESTRICT ON UPDATE CASCADE;

Answer 1

Try this (it's working for update and delete as well)
-- Generate the trigger function
CREATE OR REPLACE TRIGGER new_payroll_creation
AFTER INSERT or UPDATE or delete
ON "PayrollRow"
FOR EACH ROW
EXECUTE PROCEDURE populate_payroll_amountEur();
CREATE OR REPLACE FUNCTION populate_payroll_amounteur()
RETURNS TRIGGER
LANGUAGE PLPGSQL
AS
$$
BEGIN
UPDATE "Payroll"
SET "amountEurToPay" =
(
SELECT COALESCE(SUM("paybackEur") ,0)
FROM "PayrollRow"
WHERE "payrollId" = COALESCE( NEW."payrollId",OLD."payrollId")
)
WHERE ("id" = (COALESCE( NEW."payrollId",OLD."payrollId")));
RETURN NEW;
END;
$$