postgres updatable view and unique constraints - sql

Question

in my simple application I would like to create a view in order to allow users filling data of my db.
Here a little example of my data
CREATE TABLE specie
(
specie_id INT PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
nome_comune TEXT UNIQUE,
nome_scientifico TEXT UNIQUE
);
CREATE TABLE rilevatore
(
rilevatore_id INT PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
nome_cognome TEXT UNIQUE,
telefono INTEGER,
email TEXT,
ente_appartenenza TEXT
);
CREATE TABLE evento_investimento
(
evento_id INT PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
data DATE,
ora TIME WITHOUT TIME ZONE,
rilevatore_id INT REFERENCES rilevatore (rilevatore_id),
specie_id INT REFERENCES specie(specie_id),
);
This is the VIEW I created
CREATE VIEW investimenti_vista AS
SELECT
evento_investimento.evento_id,
evento_investimento.ora,
evento_investimento.data,
rilevatore.nome_cognome,
rilevatore.telefono,
rilevatore.email,
rilevatore.ente_appartenenza,
specie.nome_comune,
specie.nome_scientifico
from
evento_investimento
JOIN specie ON evento_investimento.specie_id = specie.specie_id
JOIN rilevatore ON evento_investimento.rilevatore_id = rilevatore.rilevatore_id;
When I attempt to fill the data I receive an error from postgres since view generated from different tables aren't updatable by default.
Thus, I implemetend the following trigger to overcome this issue.
CREATE OR REPLACE FUNCTION inserimento_vista() RETURNS trigger AS $$
BEGIN
INSERT INTO evento_investimento (data,ora)
VALUES (NEW.data,NEW.ora);
INSERT INTO rilevatore (nome_cognome, telefono, email, ente_appartenenza)
VALUES (NEW.nome_cognome, NEW.telefono, NEW.email, NEW.ente_appartenenza);
INSERT INTO specie (nome_comune, nome_scientifico)
VALUES (NEW.nome_comune, NEW.nome_scientifico);
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
create trigger inserimento_vista_trg
instead of insert on investimenti_vista for each row EXECUTE procedure inserimento_vista();
However this is not working due to unique contraints I have in the rilevatore and specie tables. How I can solve this?
Thanks

Answer 1

You might try to check for the existence of the conflicting values like this:
CREATE OR REPLACE FUNCTION inserimento_vista() RETURNS trigger AS $$
BEGIN
INSERT INTO evento_investimento (data,ora)
VALUES (NEW.data,NEW.ora);
if not exists(select * from rilevatore where rilevatore.nome_cognome=new.nome_cognome) then
INSERT INTO rilevatore (nome_cognome, telefono, email, ente_appartenenza)
VALUES (NEW.nome_cognome, NEW.telefono, NEW.email, NEW.ente_appartenenza);
end if;
if not exists(select * from specie where specie.nome_comune=new.nome_comune) then
INSERT INTO specie (nome_comune, nome_scientifico)
VALUES (NEW.nome_comune, NEW.nome_scientifico);
end if;
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
You might want to add to this an update the specie and/or rilevatore tables with the non-conflicting values but that's up to you :-)