- 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
- 122. API with NestJS #122. Many-to-many relationships with Kysely and PostgreSQL
- 123. API with NestJS #123. SQL transactions with Kysely
- 124. API with NestJS #124. Handling SQL constraints with Kysely
- 125. API with NestJS #125. Offset and keyset pagination with Kysely
- 126. API with NestJS #126. Improving the database performance with indexes and Kysely
- 127. API with NestJS #127. Arrays with PostgreSQL and Kysely
- 128. API with NestJS #128. Managing JSON data with PostgreSQL and Kysely
- 129. API with NestJS #129. Implementing soft deletes with SQL and Kysely
- 130. API with NestJS #130. Avoiding storing sensitive information in API logs
- 131. API with NestJS #131. Unit tests with PostgreSQL and Kysely
- 132. API with NestJS #132. Handling date and time in PostgreSQL with Kysely
- 133. API with NestJS #133. Introducing database normalization with PostgreSQL and Prisma
- 134. API with NestJS #134. Aggregating statistics with PostgreSQL and Prisma
- 135. API with NestJS #135. Referential actions and foreign keys in PostgreSQL with Prisma
- 136. API with NestJS #136. Raw SQL queries with Prisma and PostgreSQL range types
- 137. API with NestJS #137. Recursive relationships with Prisma and PostgreSQL
- 138. API with NestJS #138. Filtering records with Prisma
- 139. API with NestJS #139. Using UUID as primary keys with Prisma and PostgreSQL
- 140. API with NestJS #140. Using multiple PostgreSQL schemas with Prisma
- 141. API with NestJS #141. Getting distinct records with Prisma and PostgreSQL
- 142. API with NestJS #142. A video chat with WebRTC and React
- 143. API with NestJS #143. Optimizing queries with views using PostgreSQL and Kysely
- 144. API with NestJS #144. Creating CLI applications with the Nest Commander
- 145. API with NestJS #145. Securing applications with Helmet
- 146. API with NestJS #146. Polymorphic associations with PostgreSQL and Prisma
- 147. API with NestJS #147. The data types to store money with PostgreSQL and Prisma
- 148. API with NestJS #148. Understanding the injection scopes
- 149. API with NestJS #149. Introduction to the Drizzle ORM with PostgreSQL
- 150. API with NestJS #150. One-to-one relationships with the Drizzle ORM
- 151. API with NestJS #151. Implementing many-to-one relationships with Drizzle ORM
- 152. API with NestJS #152. SQL constraints with the Drizzle ORM
- 153. API with NestJS #153. SQL transactions with the Drizzle ORM
- 154. API with NestJS #154. Many-to-many relationships with Drizzle ORM and PostgreSQL
- 155. API with NestJS #155. Offset and keyset pagination with the Drizzle ORM
- 156. API with NestJS #156. Arrays with PostgreSQL and the Drizzle ORM
- 157. API with NestJS #157. Handling JSON data with PostgreSQL and the Drizzle ORM
- 158. API with NestJS #158. Soft deletes with the Drizzle ORM
- 159. API with NestJS #159. Date and time with PostgreSQL and the Drizzle ORM
- 160. API with NestJS #160. Using views with the Drizzle ORM and PostgreSQL
- 161. API with NestJS #161. Generated columns with the Drizzle ORM and PostgreSQL
- 162. API with NestJS #162. Identity columns with the Drizzle ORM and PostgreSQL
- 163. API with NestJS #163. Full-text search with the Drizzle ORM and PostgreSQL
- 164. API with NestJS #164. Improving the performance with indexes using Drizzle ORM
- 165. API with NestJS #165. Time intervals with the Drizzle ORM and PostgreSQL
- 166. API with NestJS #166. Logging with the Drizzle ORM
- 167. API with NestJS #167. Unit tests with the Drizzle ORM
- 168. API with NestJS #168. Integration tests with the Drizzle ORM
- 169. API with NestJS #169. Unique IDs with UUIDs using Drizzle ORM and PostgreSQL
- 170. API with NestJS #170. Polymorphic associations with PostgreSQL and Drizzle ORM
- 171. API with NestJS #171. Recursive relationships with Drizzle ORM and PostgreSQL
- 172. API with NestJS #172. Database normalization with Drizzle ORM and PostgreSQL
- 173. API with NestJS #173. Storing money with Drizzle ORM and PostgreSQL
Implementing relationships across tables is a crucial aspect of working with SQL databases. So far, this series covers using Kysely to design simple relationships such as one-to-one and many-to-one. This article looks into many-to-many, which is a slightly more advanced relationship.
Check out this repository if you want to see the full code from this article.
The idea behind the many-to-many relationship
We need to implement a many-to-many relationship if multiple records from one table relate to multiple records in another table. A very good example is a connection between categories and articles. A particular category can be related to various articles. On the other hand, a single article can be published under multiple categories. For example, the article you are reading falls both under the SQL and JavaScript categories.
So far, when working with Kysely, we implemented the one-to-one and many-to-one relationships. We used a simple column with a foreign key matching a row from the related table to do that.
The design becomes more complex when we want to connect a particular article to many categories. We shouldn’t put multiple IDs into the category_id column. To deal with this challenge, we need to create a joining table.
By creating the categories_articles, we can store the relationships between particular articles and categories.
Implementing the many-to-many relationship
The first step to implementing the many-to-many relationship with Kysely is to create a new migration.
20230827204025_add_categories_table.ts
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import { Kysely } from 'kysely'; export async function up(database: Kysely<unknown>): Promise<void> { await database.schema .createTable('categories') .addColumn('id', 'serial', (column) => { return column.primaryKey(); }) .addColumn('name', 'text', (column) => column.notNull()) .execute(); await database.schema .createTable('categories_articles') .addColumn('category_id', 'integer', (column) => { return column.references('categories.id').notNull(); }) .addColumn('article_id', 'integer', (column) => { return column.references('articles.id').notNull(); }) .addPrimaryKeyConstraint('primary_key', ['category_id', 'article_id']) .execute(); } export async function down(database: Kysely<unknown>): Promise<void> { await database.schema.dropTable('categories').execute(); await database.schema.dropTable('categories_articles').execute(); } |
While we could add the id column to our categories_articles table, it is unnecessary. Instead, we specify a composite primary key consisting of the category_id and article_id. This approach has more advantages than just saving disk space. Since PostgreSQL ensures a particular primary key is unique, we cannot assign an article to the category multiple times.
Besides adding a migration, we also need to create additional interfaces.
categoriesTable.ts
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import { Generated } from 'kysely'; export interface CategoriesTable { id: Generated<number>; name: string; } |
categoriesArticlesTable.ts
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export interface CategoriesArticlesTable { category_id: number; article_id: number; } |
Once we have them, we can alter our Tables interface.
database.ts
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import { ArticlesTable } from '../articles/articlesTable'; import { Kysely } from 'kysely'; import { UsersTable } from '../users/usersTable'; import { AddressesTable } from '../users/addressesTable'; import { CategoriesTable } from '../categories/categoriesTable'; import { CategoriesArticlesTable } from '../categories/categoriesArticlesTable'; interface Tables { articles: ArticlesTable; users: UsersTable; addresses: AddressesTable; categories: CategoriesTable; categories_articles: CategoriesArticlesTable; } export class Database extends Kysely<Tables> {} |
Connecting articles to categories
An article can belong to multiple different categories. Therefore, we should be able to handle the following data format when creating a new article:
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{ "title": "My first article", "content": "Hello world!", "categoryIds": [1, 2] } |
The above categoryIds array indicates that we want to add two rows to the categories_articles table.
One way of inserting multiple rows into a particular table is with a SELECT query.
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SELECT 1 as article_id, unnest(ARRAY[1,2]) AS category_id |
Above, we use the unnest function built into PostgreSQL to expand an array to a set of rows. We can now combine it with the INSERT query to save the results of the SELECT into the database.
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INSERT INTO categories_articles ( article_id, category_id ) SELECT 1 as article_id, unnest(ARRAY[1,2]) AS category_id |
Let’s use the above knowledge to create an article and connect it to multiple categories in the same query. First, let’s create a model for an article with the category ids.
articleWithCategoryIds.model.ts
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import { Article, ArticleModelData } from './article.model'; export interface ArticleWithCategoryIdsModelData extends ArticleModelData { category_ids?: number[]; } export class ArticleWithCategoryIds extends Article { categoryIds: number[]; constructor(articleData: ArticleWithCategoryIdsModelData) { super(articleData); this.categoryIds = articleData.category_ids ?? []; } } |
Now, we can add a new method to our repository that creates the article and connects it to categories with a single query.
articles.repository.ts
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import { Database } from '../database/database'; import { Injectable } from '@nestjs/common'; import { ArticleDto } from './dto/article.dto'; import { sql } from 'kysely'; import { ArticleWithCategoryIds } from './articleWithCategoryIds.model'; @Injectable() export class ArticlesRepository { constructor(private readonly database: Database) {} async createWithCategories(data: ArticleDto, authorId: number) { const databaseResponse = await this.database .with('created_article', (database) => { return database .insertInto('articles') .values({ title: data.title, article_content: data.content, author_id: authorId, }) .returningAll(); }) .with('created_relationships', (database) => { return database .insertInto('categories_articles') .columns(['article_id', 'category_id']) .expression((expressionBuilder) => { return expressionBuilder .selectFrom('created_article') .select([ 'created_article.id as article_id', sql`unnest(${data.categoryIds}::int[])`.as('category_id'), ]); }); }) .selectFrom('created_article') .select(['id', 'title', 'article_content', 'author_id']) .executeTakeFirstOrThrow(); return new ArticleWithCategoryIds({ ...databaseResponse, category_ids: data.categoryIds, }); } // ... } |
Fetching the category IDs of an article
Whenever we fetch the details of a particular article, we can attach the IDs of the related categories. The first step would be to prepare an appropriate model.
articleWithDetails.model.ts
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import { Article, ArticleModelData } from './article.model'; import { User } from '../users/user.model'; import { Type } from 'class-transformer'; interface ArticleWithDetailsModelData extends ArticleModelData { user_id: number; user_email: string; user_name: string; user_password: string; address_id: number | null; address_street: string | null; address_city: string | null; address_country: string | null; category_ids: number[] | null; } export class ArticleWithDetailsModel extends Article { @Type(() => User) author: User; categoryIds: number[]; constructor(articleData: ArticleWithDetailsModelData) { super(articleData); this.author = new User({ id: articleData.user_id, email: articleData.user_email, name: articleData.user_name, password: articleData.user_password, address_city: articleData.address_city, address_country: articleData.address_country, address_street: articleData.address_street, address_id: articleData.address_id, }); this.categoryIds = articleData.category_ids ?? []; } } |
You can go a step further and include the details of each category.
Now, we can make a separate query to fetch the categories related to a specific article.
articles.repository.ts
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import { Database } from '../database/database'; import { Injectable } from '@nestjs/common'; import { ArticleWithDetailsModel } from './articleWithDetails.model'; @Injectable() export class ArticlesRepository { constructor(private readonly database: Database) {} async getWithDetails(id: number) { const articleResponse = await this.database .selectFrom('articles') .where('articles.id', '=', id) .innerJoin('users', 'users.id', 'articles.author_id') .leftJoin('addresses', 'addresses.id', 'users.address_id') .select([ 'articles.id as id', 'articles.article_content as article_content', 'articles.title as title', 'articles.author_id as author_id', 'users.id as user_id', 'users.email as user_email', 'users.name as user_name', 'users.password as user_password', 'addresses.id as address_id', 'addresses.city as address_city', 'addresses.street as address_street', 'addresses.country as address_country', ]) .executeTakeFirst(); const categoryIdsResponse = await this.database .selectFrom('categories_articles') .where('article_id', '=', id) .selectAll() .execute(); const categoryIds = categoryIdsResponse.map( (response) => response.category_id, ); if (articleResponse) { return new ArticleWithDetailsModel({ ...articleResponse, category_ids: categoryIds, }); } } // ... } |
The above queries would benefit from wrapping them in a transaction. This is a broad topic that deserves a separate article.
Fetching all articles from a certain category
Another feature that might be needed is getting a list of all articles from a particular category. To achieve it, we need to join the data from the articles table with categories_articles. First, we need to retrieve all article IDs from a specific category.
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SELECT article_id FROM categories_articles WHERE category_id = 1 |
Since we now know the IDs of all articles, we can use the JOIN statement to match them with the rows from the articles table.
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SELECT articles.id AS article_id, articles.title AS article_title, articles.article_content AS article_content, articles.author_id AS author_id FROM categories_articles JOIN articles ON articles.id=categories_articles.article_id WHERE category_id = 1 |
Let’s create a new model suitable for the above data.
categoryWithArticles.model.ts
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import { Category, CategoryModelData } from './category.model'; import { Article, ArticleModelData } from '../articles/article.model'; export interface CategoryWithArticlesModelData extends CategoryModelData { articles: ArticleModelData[]; } class CategoryWithArticles extends Category { articles: Article[]; constructor(categoryData: CategoryWithArticlesModelData) { super(categoryData); this.articles = categoryData.articles.map((articleData) => { return new Article(articleData); }); } } export default CategoryWithArticles; |
Now, we can use all of the above knowledge to:
- retrieve the data of a specific category,
- match it with the articles,
- fit the data into the new model.
categories.response.ts
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import { Database } from '../database/database'; import { Injectable } from '@nestjs/common'; import CategoryWithArticles from './categoryWithArticles.model'; @Injectable() export class CategoriesRepository { constructor(private readonly database: Database) {} async getWithArticles(categoryId: number) { const categoryResponse = await this.database .selectFrom('categories') .where('id', '=', categoryId) .selectAll() .executeTakeFirst(); if (!categoryResponse) { return; } const articlesResponse = await this.database .selectFrom('categories_articles') .innerJoin('articles', 'articles.id', 'categories_articles.article_id') .where('category_id', '=', categoryId) .select([ 'articles.id as id', 'articles.title as title', 'articles.article_content as article_content', 'articles.author_id as author_id', ]) .execute(); return new CategoryWithArticles({ ...categoryResponse, articles: articlesResponse, }); } // ... } |
Summary
In this article, we’ve explained the many-to-many relationship and implemented it in a project with Kysely and NestJS. When doing that, we used an example of articles and categories and learned how to manage a joining table and insert multiple records into the database with one query.
Some of the queries from this article could have been wrapped in a transaction, which deserves a separate article. Stay tuned!