Sequelize Error: "Dialect needs to be explicitly supplied as of v4.0.0" when using config.ts with dotenv-flow

Question

I'm working on a Node.js project with TypeScript, Sequelize, and PostgreSQL. I encountered the following error when running my application:

ERROR: Dialect needs to be explicitly supplied as of v4.0.0

Here are the relevant files:

config/config.ts:

import dotenv from "dotenv-flow";
import { Dialect } from "sequelize";

dotenv.config();

type Config = {
    [key in "development" | "test" | "production"]: {
        username: string;
        password?: string;
        database: string;
        host: string;
        dialect: Dialect;
    };
};

const config: Config = {
    development: {
        username: process.env.PSQL_USERNAME || "root",
        password: process.env.PSQL_PASSWORD || undefined,
        database: process.env.PSQL_DATABASE || "database_development",
        host: process.env.PSQL_HOST || "127.0.0.1",
        dialect: "postgres" as Dialect,
    },
    test: {
        username: process.env.PSQL_USERNAME || "root",
        password: process.env.PSQL_PASSWORD || undefined,
        database: process.env.PSQL_DATABASE || "database_test",
        host: process.env.PSQL_HOST || "127.0.0.1",
        dialect: "postgres" as Dialect,
    },
    production: {
        username: process.env.PSQL_USERNAME || "root",
        password: process.env.PSQL_PASSWORD || undefined,
        database: process.env.PSQL_DATABASE || "database_production",
        host: process.env.PSQL_HOST || "127.0.0.1",
        dialect: "postgres" as Dialect,
    },
};

export default config;

models/index.ts:

import config from "../config/config";
import { Sequelize, DataTypes } from "sequelize"; // Import DataTypes directly
import * as fs from "fs";
import * as path from "path";
import { Dialect } from "sequelize";

const basename = path.basename(__filename);

// Define possible environment types
type Environment = "development" | "test" | "production";

// Cast process.env.NODE_ENV to one of these types, defaulting to "development"
const env: Environment = (process.env.NODE_ENV as Environment) || "development";
const dbConfig = config[env];

// Initialize Sequelize
const sequelize = new Sequelize(dbConfig.database, dbConfig.username, dbConfig.password, {
    host: dbConfig.host,
    dialect: dbConfig.dialect as Dialect,
});

// Define the db object to store the models
const db: { [key: string]: any } = {};

// Dynamically import models
fs.readdirSync(__dirname)
    .filter((file) => {
        return (
            file.indexOf(".") !== 0 &&
            file !== basename &&
            (file.slice(-3) === ".ts" || file.slice(-3) === ".js") // Consider both .ts and .js files for TypeScript
        );
    })
    .forEach(async (file) => {
        const model = (await import(path.join(__dirname, file))).default(
            sequelize,
            DataTypes
        );
        db[model.name] = model;
    });

// Setup associations if they exist
Object.keys(db).forEach((modelName) => {
    if (db[modelName].associate) {
        db[modelName].associate(db);
    }
});

// Export Sequelize and the db object
db.sequelize = sequelize;
db.Sequelize = Sequelize;

export default db;

I’ve specified the dialect in my config.ts file, but I still get the error. I am using dotenv-flow to manage environment variables and my .env files are set correctly.

I initially tried running the project with the configuration file as config.js, and in that case, everything worked fine. The migrations and seeding ran without any issues. However, when I tried to call the database sync function in app.ts, I encountered a different issue related to the require function.

Specifically, I got an error in models/index.ts where I had:

const config = require('../config/config.js');

Since require doesn't work well with TypeScript when importing from a .js file, the application couldn't load the config properly got error.

To resolve this, I refactored the configuration into a config.ts file. After this change, the database sync function in app.ts started working correctly, but now the migrations and seeding processes stopped working, and "Dialect needs to be explicitly supplied" error. in that context.

I want to fix this error so that both the database sync function in `app.ts` and the migrations/seeding processes work correctly with my `config.ts` file.