i am working on foreign data wrappers in postgres, using multicorn and using triggers to insert data in foreign tables, however i do not want the postgres to wait for response after trigger, just trigger inserts it and then forgets.
how can that be possible.
Actually i am using it for a foreign table
CREATE FOREIGN TABLE media_es (
id BIGINT,
title TEXT,
description TEXT,
tags TEXT,
query TEXT,
score NUMERIC
)
SERVER multicorn_es
OPTIONS (
host 'elasticsearch',
port '9200',
index 'test',
type 'media',
rowid_column 'id',
query_column 'query',
score_column 'score'
);
CREATE TRIGGER es_insert_media
AFTER INSERT
ON media
FOR EACH ROW
EXECUTE PROCEDURE index_media();
CREATE OR REPLACE FUNCTION index_media()
RETURNS trigger
AS $def$
BEGIN
INSERT INTO media_es
(
id,
title,
description,
tags
)
VALUES
(
NEW.id,
NEW.title,
NEW.description,
NEW.tags
)
;
RETURN NEW;
END;
$def$ LANGUAGE plpgsql;
postgres dblink extension allows async calls to remote server via dblink-send-query command.
not sure how it will work within trigger in terms of establishing multiple connections. caution should be taken here for resource leakage
Related
I have two databases: let's call them primary (which holds actual data) and fdw (which contains foreign-data-wrapper of data in primary db).
I create simple table in primary db:
create schema myschema;
create table myschema.foo (id bigint, whatever text);
create table myschema.foov as select * from foo;
I create foreign table in fdw db accessing primary table through view:
create extension postgres_fdw;
create server remote_docker foreign data wrapper postgres_fdw options (host 'primary', dbname 'postgres', port '5432');
create schema remote_myschema;
create user mapping for current_user server remote_docker options (user 'postgres');
create foreign table remote_myschema.foo (id bigint, whatever text) server remote_docker options (schema_name 'myschema', table_name 'foov');
When executing select * from remote_myschema.foo query, everything works ok.
The problem: if I didn't create view in primary db, the create foreign table command in fdw db passes without error anyway. I am able to discover the nonexistency of view in primary db only at time of query execution on fdw db.
The question: is somehow possible to detect that foreign table is bound to nonexistent original? I compared pg_class data of foreign table in both cases and didn't find any difference nor anything in documentation. The only way I know at this moment is catching exception
do $$
declare
ex boolean;
begin
begin
execute 'select null from remote_myschema.foo';
ex := true;
exception when others then
ex := false;
end;
raise notice '%', ex::text;
end;
$$;
which is awful.
Thanks!
Catching the exception is the only way. Unless views are in the habit of suddenly disappearing at your site, you don't have to test it every time you use the foreign table. Testing once, right after you created it, is good enough.
I would like to use postgres_fdw and house a FOREIGN TABLE in my database. Is it possible to define a trigger on the local server for this FOREIGN TABLE that recognizes an INSERT event on the remote server. If so, please provide an example.
Data Flow:
Insert data into table on remote server.
Recognize insert on local server's foreign table which fires a trigger.
Trigger function writes data into some other table.
Upon write success, post back to the foreign table
Idea as a crude diagram:
No error is reported but the write to table_b seems unsuccessful.
Here is what I've tried:
CREATE FOREIGN TABLE x.table_a -- note the foreign table is in a different schema than the local table
( id BIGINT NOT NULL
, data_ts TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP
, xchg_ts TIMESTAMPTZ DEFAULT NULL
)
SERVER remote_server
OPTIONS (schema_name 'schema_a', table_name 'table_a')
;
CREATE TABLE y.table_b
( xchg_id BIGINT
, error_msg TEXT DEFAULT NULL
);
CREATE OR REPLACE FUNCTION func_foreign_table_a_after_insert()
RETURNS TRIGGER
AS $$
BEGIN
INSERT INTO y.table_b
(xchg_id)
VALUES
(NEW.id)
;
RETURN NEW;
END;
$$ LANGUAGE PLPGSQL
;
CREATE TRIGGER trig_foreign_table_a_after_insert
AFTER INSERT ON x.table_a
FOR EACH ROW EXECUTE PROCEDURE func_foreign_table_a_after_insert();
I want to create an immutable Postgres database, where the user can insert & select (write & read) data, but cannot update or delete the data.
I am aware of the FOR UPDATE lock, but I don't understand how to use it.
Let's say for example I have the table below, how can I make it immutable (or, if I understood correctly, how can I use the FOR UPDATE lock permanently)
CREATE TABLE account(
user_id serial PRIMARY KEY,
username VARCHAR (50) UNIQUE NOT NULL,
password VARCHAR (50) NOT NULL,
email VARCHAR (355) UNIQUE NOT NULL,
created_on TIMESTAMP NOT NULL,
last_login TIMESTAMP
);
The solution is to give the user that accesses the database only the INSERT and SELECT privilege on the tables involved.
A lock is not a tool to deny somebody access, but a short-time barrier to prevent conflicting data modifications to happen at the same time.
Here is an example:
CREATE TABLE sensitive (
id bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
available text,
restricted text
);
Now I want to allow someuser to insert data and read and update all columns except restricted, and I want to keep myself from deleting data in that table:
/* the CREATE TABLE above was run by user "laurenz" */
REVOKE DELETE ON sensitive FROM laurenz;
GRANT INSERT ON sensitive TO someuser;
GRANT SELECT (id, available), UPDATE (id, available) ON sensitive TO someuser;
Nope, that 👆🏼 solution doesn't work. I found this one. I make a before trigger on the table on update for each row:
create or replace function table_update_guard() returns trigger
language plpgsql immutable parallel safe cost 1 as $body$
begin
raise exception
'trigger %: updating is prohibited for %.%',
tg_name, tg_table_schema, tg_table_name
using errcode = 'restrict_violation';
return null;
end;
$body$;
create or replace trigger account_update_guard
before update on account for each row
execute function table_update_guard();
See my original research.
I have a following situation.
In database A on server I, let's call it Host DB, there is a table, that has a following sample create script:
CREATE TABLE public.some_table (
id SERIAL PRIMARY KEY,
some_field TEXT
);
CREATE INDEX public.some_field_index
ON public.some_table USING btree
(my_custom_function(some_field));
As you can see, the index is created on a result of some custom, stored in database A, function my_custom_function.
Now I want to declare some_table as foreign table on other server, in database B. After creating the server, user mappings etc. I declare foreign table as:
CREATE FOREIGN TABLE public.some_table (
id SERIAL PRIMARY KEY,
some_field TEXT
)
SERVER host_server
OPTIONS (
schema_name 'public',
table_name 'some_table'
);
The table is created nicely, however I cannot query it. Instead I am getting following error:
ERROR: function my_custom_function(text) does not exist.
No function matches the given name and argument type.
You might need to add explcit type casts.
CONTEXT: Remote SQL command: SELECT id, some_field FROM public.some_table
SQL fuction my_custom_function during inlining.
I believe the problem is related to function my_custom_function not being declared on the server B, in the "guest" database. For some reasons i don't want to create this function. Is there any solution to overcome this problem?
Thanks for all your answers in advance.
I've two tables accounts and projects:
create table accounts (
id bigserial primary key,
slug text unique
);
create table projects (
id bigserial primary key,
account_id bigint not null references accounts (id),
name text
);
I want to be able to insert a new row into projects by specifying only account.slug (not account.id). What I'm trying to achieve is something like:
INSERT into projects (account_slug, name) values ('account_slug', 'project_name');
I thought about using a trigger (unfortunately it doesn't work):
create or replace function trigger_projects_insert() returns trigger as $$
begin
if TG_OP = 'INSERT' AND NEW.account_slug then
select id as account_id
from accounts as account
where account.slug = NEW.account_slug;
NEW.account_id = account_id;
-- we should also remove NEW.account_slug but don't know how
end if;
return NEW;
end;
$$ LANGUAGE plpgsql;
create trigger trigger_projects_insert before insert on projects
for each row execute procedure trigger_projects_insert();
What is the best way to achieve what I'm trying to do?
Is a trigger a good idea?
Is there any other solution?
WITH newacc AS (
INSERT INTO accounts (slug)
VALUES ('account_slug')
RETURNING id
)
INSERT INTO projects (account_id, name)
SELECT id, 'project_name'
FROM newacct;
If you are limited in the SQL you can use, another idea might be to define a view over both tables and create an INSTEAD OF INSERT trigger on the view that performs the two INSERTs on the underlying tables. Then an INSERT statement like the one in your question would work.