Learnings.MD

Sequelize

Connecting to db:

• Create a sequelize instance using database, user, password, port, host, dialect
• Run the sequelize.authenticate() function to attempt to connect to the database

Schema:

• Docs: https://sequelize.org/docs/v6/core-concepts/model-basics/
• Each table is a class. They can be extended from the Sequelize Model class
• Run the init() function, to specify the columns and their data types
• Another way, is to run the define() function

Migration:

• Docs: https://sequelize.org/docs/v6/other-topics/migrations
• To run the migration scripts, you need to install sequelize-cli
• To run the migration, the following files must be present:
  • config, contains config file, which tells CLI how to connect with database
  • models, contains all models for your project
  • migrations, contains all migration files
  • seeders, contains all seed files
  • If the files are not at the default file location, create a .sequelizerc file and specify the location of the files
• Each migration script contains the up and down function. And uses the Sequelize QueryInterface to interact with the database tables
• Note: The ./config/config.json file can actually contain config for multiple environments, instead of just one here. The ENVIRONMENT variable under .env file will then tell sequelize which config to use

Note: sequlize-cli actually has functions to create models and migration scripts by running the model:generate command. But, it is not used here as we are using TypeScript. Hence, models must be written by hand. The migration script was written to automate the generation of the migration template

pgtools

• pgtools is a npm package that allows us to connect to the db
• In our case, scripts are written to create and drop the db
• However, sequelize-cli also has a command to do so. But I have not tried them yet

PostgreSQL

• template0 and template1 are template tables provided by postgres when installed
• DO NOT delete them, if not you will not be able to create new db
• To connect to your db, run the psql -d <DATABASE_NAME> -U <USER_NAME. By default, postgres should create a postgres user and db. Hence, running psql -d postgres -U postgres should allow you to enter the psql client via terminal

Express

• Middleware: To create a controller, it is better to use a middleware to specify the controller logic. A middleware is just a function that takes in req, res and next. If there are multiple middlewares, the middlewares expect the last one, will need to call next(). But for our controller, no need to call next(). req and res functions remain the same.