- 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
In this series, we’ve often had to filter the records in our database. We can achieve that with a simple WHERE clause.
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SELECT * FROM posts WHERE author_id = 1 |
In this article, we go through different use cases of more advanced filtering. We achieve it by using the WHERE keyword with subqueries.
EXISTS
In some of the previous parts of this series, we’ve defined the posts table.
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CREATE TABLE posts ( id int GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY, title text NOT NULL, post_content text NOT NULL, author_id int REFERENCES users(id) NOT NULL ) |
The EXISTS keyword returns true if the provided subquery returns at least one record. For example, we can use it to get a list of users that wrote at least one post.
To keep our codebase clean, let’s create a designated controller to manage post statistics.
postsStatistics.controller.ts
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import { ClassSerializerInterceptor, Controller, Get, UseInterceptors } from "@nestjs/common"; import PostsStatisticsService from './postsStatistics.service'; @Controller('posts-statistics') @UseInterceptors(ClassSerializerInterceptor) export default class PostsStatisticsController { constructor( private readonly postsStatisticsService: PostsStatisticsService, ) {} @Get('users-with-any-posts') getAuthorsWithAnyPosts() { return this.postsStatisticsService.getAuthorsWithAnyPosts(); } } |
To get a list of users that wrote at least one post, we need to write a subquery that receives a list of posts by a given user.
postsStatistics.repository.ts
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import { Injectable } from '@nestjs/common'; import DatabaseService from '../database/database.service'; import UserModel from '../users/user.model'; @Injectable() class PostsStatisticsRepository { constructor(private readonly databaseService: DatabaseService) {} async getAuthorsWithAnyPosts() { const databaseResponse = await this.databaseService.runQuery(` SELECT * FROM users WHERE EXISTS ( SELECT id FROM posts WHERE posts.author_id=users.id ) `); return databaseResponse.rows.map( (databaseRow) => new UserModel(databaseRow), ); } } export default PostsStatisticsRepository; |
By using the EXIST keyword, we filter out the users for which the subquery does not return any records. By doing that, we achieved a list of users that wrote at least one post.
We can reverse the above logic by using NOT EXIST to get a list of users that didn’t write any posts.
postsStatistics.repository.ts
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import { Injectable } from '@nestjs/common'; import DatabaseService from '../database/database.service'; import UserModel from '../users/user.model'; @Injectable() class PostsStatisticsRepository { constructor(private readonly databaseService: DatabaseService) {} async getAuthorsWithoutAnyPosts() { const databaseResponse = await this.databaseService.runQuery(` SELECT * FROM users WHERE NOT EXISTS ( SELECT id FROM posts WHERE posts.author_id=users.id ) `); return databaseResponse.rows.map( (databaseRow) => new UserModel(databaseRow), ); } // ... } export default PostsStatisticsRepository; |
Subqueries with JOIN
We can use subqueries that are a lot more complex than the example above. For example, let’s get a list of users that wrote a post in a specific category.
postsStatistics.controller.ts
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import { ClassSerializerInterceptor, Controller, Get, Param, UseInterceptors, } from '@nestjs/common'; import PostsStatisticsService from './postsStatistics.service'; import IdParams from './idParams'; @Controller('posts-statistics') @UseInterceptors(ClassSerializerInterceptor) export default class PostsStatisticsController { constructor( private readonly postsStatisticsService: PostsStatisticsService, ) {} @Get('users-with-posts-in-category/:id') getAuthorsWithoutPostsInCategory(@Param() { id: categoryId }: IdParams) { return this.postsStatisticsService.getAuthorsWithPostsInCategory( categoryId, ); } // ... } |
For the above method to work as expected, we’ve defined the IdParams class. Its purpose is to convert the param from a string to a number.
categorytIdParams.ts
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import { IsNumber } from 'class-validator'; import { Transform } from 'class-transformer'; class IdParams { @IsNumber() @Transform(({ value }) => Number(value)) id: number; } export default IdParams; |
Thanks to the above, we can now use the category id in our subquery.
postsStatistics.repository.ts
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import { Injectable } from '@nestjs/common'; import DatabaseService from '../database/database.service'; import UserModel from '../users/user.model'; @Injectable() class PostsStatisticsRepository { constructor(private readonly databaseService: DatabaseService) {} async getAuthorsWithPostsInCategory(categoryId: number) { const databaseResponse = await this.databaseService.runQuery( ` SELECT email FROM users WHERE EXISTS ( SELECT * FROM posts JOIN categories_posts ON posts.id = categories_posts.post_id WHERE posts.author_id = users.id AND categories_posts.category_id = $1 ) `, [categoryId], ); return databaseResponse.rows.map( (databaseRow) => new UserModel(databaseRow), ); } // ... } export default PostsStatisticsRepository; |
IN
By using the IN keyword, we can check if any of the rows returned by a subquery matches a particular column. For example, let’s get a list of users who wrote a post longer than 100 characters.
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SELECT * FROM users WHERE id IN ( SELECT posts.author_id FROM posts WHERE length(posts.post_content) > 100 ) |
Let’s take this concept further and accept a parameter with the desired length of the post.
postsStatistics.controller.ts
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import { ClassSerializerInterceptor, Controller, Get, Param, Query, UseInterceptors, } from '@nestjs/common'; import PostsStatisticsService from './postsStatistics.service'; import PostLengthParam from './postLengthParam'; @Controller('posts-statistics') @UseInterceptors(ClassSerializerInterceptor) export default class PostsStatisticsController { constructor( private readonly postsStatisticsService: PostsStatisticsService, ) {} @Get('users-with-posts-longer-than') getAuthorsWithPostsLongerThan(@Query() { postLength }: PostLengthParam) { return this.postsStatisticsService.getAuthorsWithPostsLongerThan( postLength, ); } // ... } |
Above, we use the PostLengthParam class that defines the postLength param and transforms it from a string to a number.
postLengthParam.ts
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import { Transform } from 'class-transformer'; import { IsNumber, Min } from 'class-validator'; class PostLengthParam { @IsNumber() @Min(1) @Transform(({ value }) => Number(value)) postLength: number; } export default PostLengthParam; |
Thanks to the above, we can now use the IN keyword in a query with the postLength argument.
postsStatistics.repository.ts
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import { Injectable } from '@nestjs/common'; import DatabaseService from '../database/database.service'; import UserModel from '../users/user.model'; @Injectable() class PostsStatisticsRepository { constructor(private readonly databaseService: DatabaseService) {} async getAuthorsWithPostsLongerThan(postLength: number) { const databaseResponse = await this.databaseService.runQuery( ` SELECT email FROM users WHERE id IN ( SELECT posts.author_id FROM posts WHERE length(posts.post_content) >= $1 ) `, [postLength], ); return databaseResponse.rows.map( (databaseRow) => new UserModel(databaseRow), ); } // ... } export default PostsStatisticsRepository; |
ANY
By using the ANY keyword, we can check if any of the rows returned by a subquery matches a specific condition. When used with the = operator, it acts as the IN keyword.
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import { Injectable } from '@nestjs/common'; import DatabaseService from '../database/database.service'; import UserModel from '../users/user.model'; @Injectable() class PostsStatisticsRepository { constructor(private readonly databaseService: DatabaseService) {} async getAuthorsWithPostsLongerThan(postLength: number) { const databaseResponse = await this.databaseService.runQuery( ` SELECT email FROM users WHERE id = ANY ( SELECT posts.author_id FROM posts WHERE length(posts.post_content) >= $1 ) `, [postLength], ); return databaseResponse.rows.map( (databaseRow) => new UserModel(databaseRow), ); } // ... } export default PostsStatisticsRepository; |
The ANY keyword is more versatile than IN, though. We can use it with operators such as < and >. We can also use them when working with the ALL keyword.
ALL
When we use the ALL keyword, we check if all of the subquery results match a given condition. An example would be fetching a list of posts shorter than the posts of a given user.
postsStatistics.repository.ts
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import { Injectable } from '@nestjs/common'; import DatabaseService from '../database/database.service'; import PostModel from './post.model'; @Injectable() class PostsStatisticsRepository { constructor(private readonly databaseService: DatabaseService) {} async getPostsShorterThanPostsOfAGivenUser(userId: number) { const databaseResponse = await this.databaseService.runQuery( ` SELECT title FROM posts WHERE length(post_content) < ALL ( SELECT length(post_content) FROM posts WHERE author_id = $1 ) `, [userId], ); return databaseResponse.rows.map( (databaseRow) => new PostModel(databaseRow), ); } // ... } export default PostsStatisticsRepository; |
The above query might run for quite a bit of time without appropriate indexes. If you want to know more about how to optimize our queries for performance, check out API with NestJS #82. Introduction to indexes with raw SQL queries
The ALL keyword would also be a good choice when we expect our subquery to return just one result. For example, let’s find the users that wrote posts shorter than average.
postsStatistics.repository.ts
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import { Injectable } from '@nestjs/common'; import DatabaseService from '../database/database.service'; import UserModel from '../users/user.model'; @Injectable() class PostsStatisticsRepository { constructor(private readonly databaseService: DatabaseService) {} async getUsersWithPostsShorterThanAverage() { const databaseResponse = await this.databaseService.runQuery( ` SELECT email FROM users JOIN posts ON posts.author_id = users.id GROUP BY email HAVING avg(length(post_content)) < ALL ( SELECT avg(length(post_content)) FROM POSTS ) `, [], ); return databaseResponse.rows.map( (databaseRow) => new UserModel(databaseRow), ); } // ... } export default PostsStatisticsRepository; |
Summary
In this article, we’ve gone through more advanced filtering using the WHERE keyword and subqueries. When doing that, we’ve gone through examples of using the EXISTS, IN, ANY, and ALL keywords. All of the above can come in handy when generating statistics.