PostgreSQL 数据库播种器在第二次运行后抛出“触发“trigger_test_genid”关系“test”已经存在”

Question

I'm trying to implement a database seeder which will run every time the server starts. The seeder basically installs an extension and then makes a function to generate random short ids (got the function from a blog) for table data. And then it creates a table and inserts something.

So when the server starts for the first time, it will check if the extension is installed and the table exists or not. If it does then it will do nothing. If it doesn't then it will install the extension, create a table and insert some initial data.

Right now when it starts the first time, it does what I want it to do. But when it runs the second time then it throws this error trigger "trigger_test_genid" for relation "test" already exists .

I've tried putting IF NOT EXISTS in CREATE TRIGGER but apparently create trigger does not take in IF NOT EXISTS and throws a different error.

I have also tried doing an if statement that when an extension with the name of pgcrypto exists then return and not run the rest of the code. But that won't work cause the user might have pgcrypto installed in their database for other purposes.

Here's the full code:

const pool = require('./db');
const createExt = `
                CREATE EXTENSION IF NOT EXISTS "pgcrypto";
            `; 

const createExtFunc = `
                CREATE OR REPLACE FUNCTION unique_short_id()
                RETURNS TRIGGER AS $$
                DECLARE
                  key TEXT;
                  qry TEXT;
                  found TEXT;
                BEGIN
                    qry := 'SELECT id FROM ' || quote_ident(TG_TABLE_NAME) || ' WHERE id=';

                    LOOP

                        key := encode(gen_random_bytes(6), 'base64');
                        key := replace(key, '/', '_'); 
                        key := replace(key, '+', '-'); 

                        EXECUTE qry || quote_literal(key) INTO found;

                        IF found IS NULL THEN
                            EXIT;
                        END IF;

                    END LOOP;
                    NEW.id = key;
                    RETURN NEW;
                END;
                $$ language 'plpgsql';
            `;

const createDemoTable = `
                    CREATE TABLE IF NOT EXISTS test (id TEXT PRIMARY KEY, name TEXT);
                    CREATE TRIGGER trigger_test_genid BEFORE INSERT ON test FOR EACH ROW EXECUTE PROCEDURE unique_short_id();
                `; 

const demoInsert = `
                    INSERT INTO test (name) VALUES ('cheese'), ('ham'), ('turkey'), ('chicken');
                    SELECT * FROM test;
                `;


const dbSeeder = async () => {
    try{
        await pool.query(createExt);
        await pool.query(createExtFunc);
        await pool.query(createDemoTable);
        await pool.query(demoInsert);

        const results = await pool.query('SELECT * FROM test');

        console.log('Data seeded successfully!', results.rows);
    }catch(e) {
        console.log(e);
    }
};


module.exports = dbSeeder;

So how can I run the seeder for the first time only and do nothing on the rest of the time? And also put a log as well that says Data exists. No need to seed. Data exists. No need to seed.

PS. I'm a noob in PGSQL. This is my first learning project based on PEN Stack. So please give me beginner friendly solutions. Thanks

Answer 1

I'm trying to implement a database seeder which will run every time the server starts. The seeder basically installs an extension and then makes a function to generate random short ids (got the function from a blog) for table data. And then it creates a table and inserts something.

So when the server starts for the first time, it will check if the extension is installed and the table exists or not. If it does then it will do nothing. If it doesn't then it will install the extension, create a table and insert some initial data.

Right now when it starts the first time, it does what I want it to do. But when it runs the second time then it throws this error trigger "trigger_test_genid" for relation "test" already exists .

I've tried putting IF NOT EXISTS in CREATE TRIGGER but apparently create trigger does not take in IF NOT EXISTS and throws a different error.

I have also tried doing an if statement that when an extension with the name of pgcrypto exists then return and not run the rest of the code. But that won't work cause the user might have pgcrypto installed in their database for other purposes.

Here's the full code:

const pool = require('./db');
const createExt = `
                CREATE EXTENSION IF NOT EXISTS "pgcrypto";
            `; 

const createExtFunc = `
                CREATE OR REPLACE FUNCTION unique_short_id()
                RETURNS TRIGGER AS $$
                DECLARE
                  key TEXT;
                  qry TEXT;
                  found TEXT;
                BEGIN
                    qry := 'SELECT id FROM ' || quote_ident(TG_TABLE_NAME) || ' WHERE id=';

                    LOOP

                        key := encode(gen_random_bytes(6), 'base64');
                        key := replace(key, '/', '_'); 
                        key := replace(key, '+', '-'); 

                        EXECUTE qry || quote_literal(key) INTO found;

                        IF found IS NULL THEN
                            EXIT;
                        END IF;

                    END LOOP;
                    NEW.id = key;
                    RETURN NEW;
                END;
                $$ language 'plpgsql';
            `;

const createDemoTable = `
                    CREATE TABLE IF NOT EXISTS test (id TEXT PRIMARY KEY, name TEXT);
                    CREATE TRIGGER trigger_test_genid BEFORE INSERT ON test FOR EACH ROW EXECUTE PROCEDURE unique_short_id();
                `; 

const demoInsert = `
                    INSERT INTO test (name) VALUES ('cheese'), ('ham'), ('turkey'), ('chicken');
                    SELECT * FROM test;
                `;


const dbSeeder = async () => {
    try{
        await pool.query(createExt);
        await pool.query(createExtFunc);
        await pool.query(createDemoTable);
        await pool.query(demoInsert);

        const results = await pool.query('SELECT * FROM test');

        console.log('Data seeded successfully!', results.rows);
    }catch(e) {
        console.log(e);
    }
};


module.exports = dbSeeder;

So how can I run the seeder for the first time only and do nothing on the rest of the time? And also put a log as well that says Data exists. No need to seed. Data exists. No need to seed.

PS. I'm a noob in PGSQL. This is my first learning project based on PEN Stack. So please give me beginner friendly solutions. Thanks