liviaerxin / node-postgres-data-access-layer

Data Access Layer(DAL) in Node.js with PostgreSQL

Data Access Layer in Node.js with PostgreSQL

The repo will build a simply Data Access Layer from scratch, using only node-postgresql. To attain a comprehensive understanding, you can go deep into popular ORM libraries such TypeORM

The Data Access Layer(DAL), a.k.a. Data Access Object(DAO) in Java development environment, is a very important part of any application, which provides simplified access to data stored in a persistent storage like relational database. It is often sits between business logic layer(BLL) and the external database, and abstract executed SQL statement(SELECT, UPDATE, INSERT, DELETE) into simple functions like readUser() and addUser().

For the data transfer between DAL and database, an in-memory object in DAL (in terms of object-oriented programming) complete with its attributes will correspond with a row of fields from a database table.

There are two patterns to implement the DAL: Active Record and Data Mapper patterns, most ORM tools follow these two, especially the later.

This demo will choose Data Mapper pattern, and have modern niceties:

• TypeScript in whole.
• Tests using mocha and chaia, and integrating a PostgreSQL database.
• Tests in CI/CD.

Let's get started!

The following example code is in GitHub - liviaerxin/node-postgres-data-access-layer.

Project Structure

./
├── src
│   ├── db
│   │   ├── index.ts
│   │   └── userDao.ts
│   └── model
│       └── User.ts
├── test
│   ├── test.ts
│   └── userDao.ts
├── package.json
└── tsconfig.json

Starting the Project

1. Initialize the Node.js project

npx gitignore node
npm init

It will generate the package.json file.

2. Initialize the TypeScript

npx tsc --init

It will generate the tsconfig.json file.

Test

In local, start a database in first. Using Docker is absolutely convenient and fast.

Here the docker-compose.yml file is ready to use, just run,

docker compose up

Then run tests,

npm run test

NOTE: Due to mocha doesn't run TypeScript directly, the test should be able to run after compiling *.ts to generate *.js by running tsc && mocha dist/test. Alternatively, the test can run without generating *.js files in such dist folder by running mocha --require ts-node/register dist/test which is required to install ts-node package.