TypeScript compile problems with node-postgres

Question

Disclaimer up-front, I'm fairly new to TypeScript so this may be a dumb question!

I'm attempting to use the same setup for my Express/Postgres application as described in the node-postgres docs, where I have a single module that connects to the PostgreSQL server and is included wherever I need to access it, but I'm having some trouble with TypeScript's types.

For this example I've simplified everything down to entirely remove Express. If I do this everything works and TypeScript's compiler is happy:

import { Pool } from 'pg';

const pool = new Pool({
    host: process.env.PG_HOST,
    port: parseInt(process.env.PG_PORT),
    user: process.env.PG_USER,
    password: process.env.PG_PASSWORD,
    database: process.env.PG_DATABASE,
});

(async function getRows() {
    const result = await pool.query('SELECT id, message, created FROM media');

    interface dbObject {
        id: number,
        message: string,
        created: Date
    }
    await result.rows.map((row: dbObject) => {
        console.log(row.id);
        console.log(row.message);
        console.log(row.created);
    })
})()

However, if I move the pg functions into its own separate db.ts module:

import { Pool } from 'pg';

const pool = new Pool({
    host: process.env.PG_HOST,
    port: parseInt(process.env.PG_PORT),
    user: process.env.PG_USER,
    password: process.env.PG_PASSWORD,
    database: process.env.PG_DATABASE,
});

export = {
    query: (text, params) => pool.query(text, params),
}

And import it into the main app.ts file:

import database from './db';

(async function getRows() {
    const result = await database.query('SELECT id, message, created FROM media', []);

    interface dbObject {
        id: number,
        message: string,
        created: Date
    }
    await result.rows.map((row: dbObject) => {
        console.log(row.id);
        console.log(row.message);
        console.log(row.created);
    })
})()

I get several complaints:

src/app.ts:11:27 - error TS2345: Argument of type '(row: dbObject) => void' is not assignable to parameter of type '(value: any[], index: number, array: any[][]) => void'.
  Types of parameters 'row' and 'value' are incompatible.
    Type 'any[]' is missing the following properties from type 'dbObject': id, message, created

11     await result.rows.map((row: dbObject) => {
                             ~~~~~~~~~~~~~~~~~~~~


Found 1 error.

I realise it's likely because I don't have any types added to the query function in my db.ts file, but I also don't actually know how to correctly add them to make this all work!

VirtualWolf · Accepted Answer · 2019-08-01 09:27:40Z

6

Well, this seems to work! I just changed db.ts to export pool directly:

import { Pool } from 'pg';

const pool = new Pool({
    host: process.env.PG_HOST,
    port: parseInt(process.env.PG_PORT),
    user: process.env.PG_USER,
    password: process.env.PG_PASSWORD,
    database: process.env.PG_DATABASE,
});

export = pool;

answered Aug 1, 2019 at 9:27

VirtualWolf

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