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.