May 18, 2020

• 1. API with NestJS #1. Controllers, routing and the module structure
• 2. API with NestJS #2. Setting up a PostgreSQL database with TypeORM
• 3. API with NestJS #3. Authenticating users with bcrypt, Passport, JWT, and cookies
• 4. API with NestJS #4. Error handling and data validation
• 5. API with NestJS #5. Serializing the response with interceptors
• 6. API with NestJS #6. Looking into dependency injection and modules
• 7. API with NestJS #7. Creating relationships with Postgres and TypeORM
• 8. API with NestJS #8. Writing unit tests
• 9. API with NestJS #9. Testing services and controllers with integration tests
• 10. API with NestJS #10. Uploading public files to Amazon S3
• 11. API with NestJS #11. Managing private files with Amazon S3
• 12. API with NestJS #12. Introduction to Elasticsearch
• 13. API with NestJS #13. Implementing refresh tokens using JWT
• 14. API with NestJS #14. Improving performance of our Postgres database with indexes
• 15. API with NestJS #15. Defining transactions with PostgreSQL and TypeORM
• 16. API with NestJS #16. Using the array data type with PostgreSQL and TypeORM
• 17. API with NestJS #17. Offset and keyset pagination with PostgreSQL and TypeORM
• 18. API with NestJS #18. Exploring the idea of microservices
• 19. API with NestJS #19. Using RabbitMQ to communicate with microservices
• 20. API with NestJS #20. Communicating with microservices using the gRPC framework
• 21. API with NestJS #21. An introduction to CQRS
• 22. API with NestJS #22. Storing JSON with PostgreSQL and TypeORM
• 23. API with NestJS #23. Implementing in-memory cache to increase the performance
• 24. API with NestJS #24. Cache with Redis. Running the app in a Node.js cluster
• 25. API with NestJS #25. Sending scheduled emails with cron and Nodemailer
• 26. API with NestJS #26. Real-time chat with WebSockets
• 27. API with NestJS #27. Introduction to GraphQL. Queries, mutations, and authentication
• 28. API with NestJS #28. Dealing in the N + 1 problem in GraphQL
• 29. API with NestJS #29. Real-time updates with GraphQL subscriptions
• 30. API with NestJS #30. Scalar types in GraphQL
• 31. API with NestJS #31. Two-factor authentication
• 32. API with NestJS #32. Introduction to Prisma with PostgreSQL
• 33. API with NestJS #33. Managing PostgreSQL relationships with Prisma
• 34. API with NestJS #34. Handling CPU-intensive tasks with queues
• 35. API with NestJS #35. Using server-side sessions instead of JSON Web Tokens
• 36. API with NestJS #36. Introduction to Stripe with React
• 37. API with NestJS #37. Using Stripe to save credit cards for future use
• 38. API with NestJS #38. Setting up recurring payments via subscriptions with Stripe
• 39. API with NestJS #39. Reacting to Stripe events with webhooks
• 40. API with NestJS #40. Confirming the email address
• 41. API with NestJS #41. Verifying phone numbers and sending SMS messages with Twilio
• 42. API with NestJS #42. Authenticating users with Google
• 43. API with NestJS #43. Introduction to MongoDB
• 44. API with NestJS #44. Implementing relationships with MongoDB
• 45. API with NestJS #45. Virtual properties with MongoDB and Mongoose
• 46. API with NestJS #46. Managing transactions with MongoDB and Mongoose
• 47. API with NestJS #47. Implementing pagination with MongoDB and Mongoose
• 48. API with NestJS #48. Definining indexes with MongoDB and Mongoose
• 49. API with NestJS #49. Updating with PUT and PATCH with MongoDB and Mongoose
• 50. API with NestJS #50. Introduction to logging with the built-in logger and TypeORM
• 51. API with NestJS #51. Health checks with Terminus and Datadog
• 52. API with NestJS #52. Generating documentation with Compodoc and JSDoc
• 53. API with NestJS #53. Implementing soft deletes with PostgreSQL and TypeORM
• 54. API with NestJS #54. Storing files inside a PostgreSQL database
• 55. API with NestJS #55. Uploading files to the server
• 56. API with NestJS #56. Authorization with roles and claims
• 57. API with NestJS #57. Composing classes with the mixin pattern
• 58. API with NestJS #58. Using ETag to implement cache and save bandwidth
• 59. API with NestJS #59. Introduction to a monorepo with Lerna and Yarn workspaces
• 60. API with NestJS #60. The OpenAPI specification and Swagger
• 61. API with NestJS #61. Dealing with circular dependencies
• 62. API with NestJS #62. Introduction to MikroORM with PostgreSQL
• 63. API with NestJS #63. Relationships with PostgreSQL and MikroORM
• 64. API with NestJS #64. Transactions with PostgreSQL and MikroORM
• 65. API with NestJS #65. Implementing soft deletes using MikroORM and filters
• 66. API with NestJS #66. Improving PostgreSQL performance with indexes using MikroORM
• 67. API with NestJS #67. Migrating to TypeORM 0.3
• 68. API with NestJS #68. Interacting with the application through REPL
• 69. API with NestJS #69. Database migrations with TypeORM
• 70. API with NestJS #70. Defining dynamic modules
• 71. API with NestJS #71. Introduction to feature flags
• 72. API with NestJS #72. Working with PostgreSQL using raw SQL queries
• 73. API with NestJS #73. One-to-one relationships with raw SQL queries
• 74. API with NestJS #74. Designing many-to-one relationships using raw SQL queries
• 75. API with NestJS #75. Many-to-many relationships using raw SQL queries
• 76. API with NestJS #76. Working with transactions using raw SQL queries
• 77. API with NestJS #77. Offset and keyset pagination with raw SQL queries
• 78. API with NestJS #78. Generating statistics using aggregate functions in raw SQL
• 79. API with NestJS #79. Implementing searching with pattern matching and raw SQL
• 80. API with NestJS #80. Updating entities with PUT and PATCH using raw SQL queries
• 81. API with NestJS #81. Soft deletes with raw SQL queries
• 82. API with NestJS #82. Introduction to indexes with raw SQL queries
• 83. API with NestJS #83. Text search with tsvector and raw SQL
• 84. API with NestJS #84. Implementing filtering using subqueries with raw SQL
• 85. API with NestJS #85. Defining constraints with raw SQL
• 86. API with NestJS #86. Logging with the built-in logger when using raw SQL
• 87. API with NestJS #87. Writing unit tests in a project with raw SQL
• 88. API with NestJS #88. Testing a project with raw SQL using integration tests
• 89. API with NestJS #89. Replacing Express with Fastify
• 90. API with NestJS #90. Using various types of SQL joins
• 91. API with NestJS #91. Dockerizing a NestJS API with Docker Compose
• 92. API with NestJS #92. Increasing the developer experience with Docker Compose
• 93. API with NestJS #93. Deploying a NestJS app with Amazon ECS and RDS
• 94. API with NestJS #94. Deploying multiple instances on AWS with a load balancer
• 95. API with NestJS #95. CI/CD with Amazon ECS and GitHub Actions
• 96. API with NestJS #96. Running unit tests with CI/CD and GitHub Actions
• 97. API with NestJS #97. Introduction to managing logs with Amazon CloudWatch
• 98. API with NestJS #98. Health checks with Terminus and Amazon ECS
• 99. API with NestJS #99. Scaling the number of application instances with Amazon ECS
• 100. API with NestJS #100. The HTTPS protocol with Route 53 and AWS Certificate Manager
• 101. API with NestJS #101. Managing sensitive data using the AWS Secrets Manager
• 102. API with NestJS #102. Writing unit tests with Prisma
• 103. API with NestJS #103. Integration tests with Prisma
• 104. API with NestJS #104. Writing transactions with Prisma
• 105. API with NestJS #105. Implementing soft deletes with Prisma and middleware
• 106. API with NestJS #106. Improving performance through indexes with Prisma
• 107. API with NestJS #107. Offset and keyset pagination with Prisma
• 108. API with NestJS #108. Date and time with Prisma and PostgreSQL
• 109. API with NestJS #109. Arrays with PostgreSQL and Prisma
• 110. API with NestJS #110. Managing JSON data with PostgreSQL and Prisma
• 111. API with NestJS #111. Constraints with PostgreSQL and Prisma
• 112. API with NestJS #112. Serializing the response with Prisma
• 113. API with NestJS #113. Logging with Prisma
• 114. API with NestJS #114. Modifying data using PUT and PATCH methods with Prisma
• 115. API with NestJS #115. Database migrations with Prisma
• 116. API with NestJS #116. REST API versioning
• 117. API with NestJS #117. CORS – Cross-Origin Resource Sharing
• 118. API with NestJS #118. Uploading and streaming videos
• 119. API with NestJS #119. Type-safe SQL queries with Kysely and PostgreSQL
• 120. API with NestJS #120. One-to-one relationships with the Kysely query builder
• 121. API with NestJS #121. Many-to-one relationships with PostgreSQL and Kysely

The next important thing when learning how to create an API is how to store the data. In this article, we look into how to do so with PostgreSQL and NestJS. To make the managing of a database more convenient, we use an Object-relational mapping (ORM) tool called TypeORM. To have an even better understanding, we also look into some SQL queries. By doing so, we can grasp what advantages ORM gives us.

You can find all of the below code in this repository.

Creating a PostgreSQL database

The most straightforward way of kickstarting our development with a Postgres database is to use docker.
Here, we use the same setup as in the TypesScript Express series.

The first thing to do is to install Docker and Docker Compose. Now, we need to create a docker-compose file and run it.

docker-compose.yml

The useful thing about the above configuration is that it also starts a pgAdmin console. It gives us the possibility to view the state of our database and interact with it.

To provide credentials used by our Docker containers, we need to create the docker.env file. You might want to skip committing it by adding it to your .gitignore.

docker.env

Once all of the above is set up, we need to start the containers:

Environment variables

A crucial thing to running our application is to set up environment variables. By using them to hold configuration data, we can make it easily configurable. Also, it is easier to keep sensitive data from being committed to a repository.

In the Express Typescript series, we use a library called dotenv to inject our variables. In NestJS, we have a  ConfigModule that we can use in our application. It uses dotenv under the hood.

app.module.ts

As soon as we create a .env file at the root of our application, NestJS injects them into a ConfigSerivice that we will use soon.

.env

Validating environment variables

It is an excellent idea to verify our environment variables before running the application. In the TypeScript Express series, we’ve used a library called envalid.

The  ConfigModule built into NestJS supports @hapi/joi that we can use to define a validation schema.

app.module.ts

Connecting a NestJS application with PostgreSQL

A first thing to do once we have our database running is to define a connection between our application and the database. To do so, we use  TypeOrmModule.

To keep our code clean, I suggest creating a database module.

database.module.ts

The synchronize flag above is very important. We will elaborate on it a lot later

An essential thing above is that we use the ConfigModule and ConfigService. The  useFactory method can access the environment variables thanks to providing the  imports and  inject arrays. We elaborate on these mechanisms in the upcoming parts of this series.

Now, we need to import our DatabaseModule.

app.module.ts

Entities

The most crucial concept to grasp when using TypeORM is the entity. It is a class that maps to a database table. To create it, we use the  @Entity() decorator.

post.entity.ts

A neat thing about TypeORM is that it integrates well with TypeScript because it is written in it. To define our columns, we can use various decorators.

@PrimaryGeneratedColumn()

A primary key is a column used to identify a row uniquely in a table. Although we might use an existing column and make it primary, we usually create an id column. By choosing  PrimaryGeneratedColumn from TypeORM, we create an integer primary column that has a value generated automatically.

@Column()

The  @Column() decorator marks a property as a column. When using it, we have two possible approaches.

The first approach is not to pass the column type explicitly. When we do it, TypeORM figures out the column using our TypeScript types. It is possible because NestJS uses reflect-metadata under the hood.

The second approach would be to pass the type of column explicitly, for example, by using  @Column('text'). The available column types differ between databases like MySQL and Postgres. You can look them up in the TypeORM documentation.

It is a proper moment to discuss different ways to store strings in Postgres. Relying on TypeORM to figure out the type of a string column results in the “character varying” type, also called varchar.

Varchar is very similar to a text type of a column but gives us a possibility to limit the length of a string. Both types are the same performance-wise.

SQL query

In pgAdmin, we can check a query equivalent to what TypeORM did for us under the hood.

There are a few interesting things to notice above

Using  @PrimaryGeneratedColumn() results in having an int column. It defaults to the return value of a  nextval function that returns unique ids. An alternative would be to use a serial type instead and would make the query shorter, but it works the same under the hood.

Our entity has varchar columns that use COLLATE. Collation is used to specify the sort order and character classification. To see our default collation, we can run this query:

en_US.utf8

The above value is defined in a query that was used to create our database. It is UTF8 and English by default.

Also, our CREATE TABLE  query puts a constraint on our ids so that they are always unique.

PK_be5fda3aac270b134ff9c21cdee is a name of the above constraint and was generated

Repositories

With repositories, we can manage a particular entity. A repository has multiple functions to interact with entities. To access it, we use the  TypeOrmModule again.

posts.module.ts

Now, in our  PostsService, we can inject the Posts repository.

Finding

With the find function, we can get multiple elements. If we don’t provide ith with any options, it returns all.

To get just one element we use the  findOne function. By providing it with a number we indicate that we want an element with a particular id. If the result is undefined, it means that the element wasn’t found.

Creating

By using the create function, we can instantiate a new Post. We can use the save function afterward to populate the database with our new entity.

Modifying

To modify an existing element, we can use the  update function. Afterward, we would use the  findOne function to return the modified element.

A significant thing is that it accepts a partial entity, so it acts as a PATCH, not as a PUT. If you want to read more on PUT vs PATCH (although with MongoDB), check out TypeScript Express tutorial #15. Using PUT vs PATCH in MongoDB with Mongoose

Deleting

To delete an element with a given id, we can use the  delete function.

By checking out the documentation of the DELETE command, we can see that we have access to the count of removed elements. This data is available in the  affected property. If it equals zero, we can assume that the element does not exist.

Handling asynchronous errors

A beneficial thing about NestJS controllers is that they handle asynchronous errors very well.

If the  getPostById function throws an error, NestJS catches it automatically and parses it. When using pure Express, we would do this ourselves:

Summary

In this article, we’ve gone through the basics of connecting our NestJS application with a PostgreSQL database. Not only did we use TypeORM, but we’ve also looked into some SQL queries. NestJS and TypeORM have lots of features built-in and ready to use. In the upcoming parts of this series, we will look into them more, so stay tuned!

Series Navigation

<< API with NestJS #1. Controllers, routing and the module structureAPI with NestJS #3. Authenticating users with bcrypt, Passport, JWT, and cookies >>