Writing to a data table with just foreign keys - php

Question

I have a PostGreSQL database with the following data model:
CREATE TABLE staff (s_id serial UNIQUE, name, username, password, email)
CREATE TABLE institution (i_id serial UNIQUE, name);
CREATE TABLE isStaffOf (i_id, s_id); //foreign key references
When a user submits the form I have a PHP script which writes the information to first two data tables and that automatically generates the s_id and i_id values. Great!
I've tried out a few PHP modifications to get the system writing both the s_id and i_id into the isStaffOf relation so it can enforce the explicit 1..1 relationship required for my project but on submit it says I have an insufficient data type. See below for the PHP code.
$name = $_POST["name"];
$username = $_POST["username"];
$password = $_POST["password"];
$email = $_POST["email"];
$institution = $_POST["institution"];
$conn = pg_connect("host=***** port=**** dbname=****** user=**** password=******");
$staffWrite = pg_query("INSERT INTO staff(name, username, password, email) VALUES ('$name', '$username', '$password', '$email')");
$instiWrite = pg_query("INSERT INTO institution(name) VALUES ('$institution')");
$instiFK=pg_query("SELECT i_id FROM institution WHERE name='$institution'");
$staffFK=pg_query("SELECT s_id FROM staff WHERE name='$username'");
$sql=("INSERT INTO isstaffof(i_id, s_id) VALUES ('$instiFK', '$staffFK')");
$result = pg_query($sql);
That is the script I have at the moment but its not working. Any ideas on how to fix this so that when a user submits all the data tables will be filled and the referential integrity enforced? I'm almost there and still trying things out but to no avail.
The error message:
ERROR: invalid input syntax for integer: "Resource id #4" LINE 1: INSERT INTO isstaffof(i_id, s_id) VALUES ('Resource id #4', ...
Please let me know if you need more explanation but I'm sure its clear what I want to achieve and I'm convinced I can do it without so many pg_query calls.

Answer 1

As of PostgreSQL version 9.1, you can use a single query to INSERT in all 3 tables, a writable common table expression:
WITH
step_1 AS(
INSERT INTO staff (name) VALUES('Frank') RETURNING s_id
),
step_2 AS (
INSERT INTO institution (name) VALUES('PostgreSQL') RETURNING i_id
)
INSERT INTO isStaffOf (i_id, s_id) SELECT i_id,s_id FROM step_1, step_2;
Simple, fast and reliable.
You could do some other tricks as well, when some records already exists and just want to select the primary key value.

Answer 2

WHEN creating the isstaffof table, you at least have to specify the datatypes, and you can specify they are foreign keys.
CREATE TABLE isstaffof
(i_id BIGINT REFERENCES institution(i_id)
, s_id BIGINT REFERENCES staff(s_id)
);
NOTE: avoid using MixedCase for identifiers. It might cause terrible problems, if you ever have to port to a different DBMS platform.
UPDATE: Just put it in a plain INSERT INTO ... SELECT ... FROM ... statement.
CREATE TABLE staff (s_id serial UNIQUE, sname varchar);
CREATE TABLE institution (i_id serial UNIQUE, iname varchar);
CREATE TABLE isstaffof
(i_id BIGINT REFERENCES institution(i_id)
, s_id BIGINT REFERENCES staff(s_id)
);
INSERT INTO isstaffof(i_id,s_id)
SELECT i.i_id,s.s_id
FROM staff s, institution i
WHERE i.iname='$institution'
AND s.sname = '$staff'
;
Now, you can wrap that into your front-end code.

Answer 3

You'll have to fetch the result with pg_fetch_assoc or something similar. The way you're using it now you're passing the whole pg_query resource as an integer - obviously php can't convert that to a valid integer.
$name = $_POST["name"];
$username = $_POST["username"];
$password = $_POST["password"];
$email = $_POST["email"];
$institution = $_POST["institution"];
$conn = pg_connect("host=***** port=**** dbname=****** user=**** password=******");
$staffWrite = pg_query("INSERT INTO staff(name, username, password, email) VALUES ('$name', '$username', '$password', '$email')");
$instiWrite = pg_query("INSERT INTO institution(name) VALUES ('$institution')");
$instiFK=pg_query("SELECT i_id FROM institution WHERE name='$institution'");
$rowInsti = pg_fetch_assoc($instiFK);
$staffFK = pg_query("SELECT s_id FROM staff WHERE name='$username'");
$rowStaff = pg_fetch_assoc($staffFK);
$result = pg_query("INSERT INTO isstaffof(i_id, s_id) VALUES (".$rowInsti['i_id'].", ".$rowStaff['s_id'].")");
As an alternative you could probably use pg_last_oid directly after every insert to get the id. (Even more beautiful would the RETURNING-solution be. Just read the comments on the php.net page)