- 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
We need to watch out for quite a few pitfalls when designing our architecture. One of them is the possibility of circular dependencies. In this article, we go through this concept in the context of Node.js modules and NestJS services.
Circular dependencies in Node.js modules
A circular dependency between Node.js modules happens when two files import each other. Let’s look into this straightforward example:
one.js
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const { two } = require('./two'); const one = '1'; console.log('file one.js:', one, two); module.exports.one = one; |
two.js
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const { one } = require('./one'); const two = '2'; console.log('file two.js:', one, two); module.exports.two = two; |
After running node ./one.js, we see the following output:
file two.js: undefined 2
file one.js: 1 2
(node:109498) Warning: Accessing non-existent property ‘one’ of module exports inside circular dependency
(Usenode --trace-warnings ...
to show where the warning was created)
We can see that a code containing circular dependencies can run but might result in unexpected results. The above code executes as follows:
- one.js executes, and imports two.js,
- two.js executes, and imports one.js,
- to prevent an infinite loop,
two.js loads an unfinished copy of
one.js,
- this is why the one variable in two.js is undefined,
- two.js finishes executing, and its exported value reaches one.js,
- one.js continues running and contains all valid values.
The above example allows us to understand how Node.js reacts to circular dependencies. Circular dependencies are often a sign of a bad design, and we should avoid them when possible.
Detecting circular dependencies using ESLint
The provided code example makes it very obvious that there is a circular dependency between files. It is not always that apparent, though. Fortunately, ESLint can help us detect such dependencies. To do that, we need the eslint-plugin-import package.
1 |
npm install eslint-plugin-import |
The rule that we want is called import/no-cycle, and it ensures that no circular dependencies are present between our files.
In our NestJS project, we would set the configuration in the following way:
.eslintrc.js
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module.exports = { "parser": "@typescript-eslint/parser", "plugins": [ "import", // ... ], "extends": [ "plugin:import/typescript", // ... ], "rules": { "import/no-cycle": 2, // ... }, // ... }; |
Circular dependencies in NestJS
Besides circular dependencies between Node.js modules, we might also run into this issue when working with NestJS modules. In part 55 of this series, we’ve implemented a feature of uploading files to the server. Let’s expand on it to create a case with a circular dependency.
localFiles.service.js
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import { Injectable, NotFoundException } from '@nestjs/common'; import { InjectRepository } from '@nestjs/typeorm'; import { Repository } from 'typeorm'; import LocalFile from './localFile.entity'; import { UsersService } from '../users/users.service'; @Injectable() class LocalFilesService { constructor( @InjectRepository(LocalFile) private localFilesRepository: Repository<LocalFile>, private usersService: UsersService ) {} async getUserAvatar(userId: number) { const user = await this.usersService.getById(userId); return this.getFileById(user.avatarId); } async saveLocalFileData(fileData: LocalFileDto) { const newFile = await this.localFilesRepository.create(fileData) await this.localFilesRepository.save(newFile); return newFile; } async getFileById(fileId: number) { const file = await this.localFilesRepository.findOne(fileId); if (!file) { throw new NotFoundException(); } return file; } } export default LocalFilesService; |
users.service.js
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import { HttpException, HttpStatus, Injectable } from '@nestjs/common'; import { InjectRepository } from '@nestjs/typeorm'; import { Repository } from 'typeorm'; import User from './user.entity'; import LocalFilesService from '../localFiles/localFiles.service'; @Injectable() export class UsersService { constructor( @InjectRepository(User) private usersRepository: Repository<User>, private localFilesService: LocalFilesService ) {} async getById(id: number) { const user = await this.usersRepository.findOne({ id }); if (user) { return user; } throw new HttpException('User with this id does not exist', HttpStatus.NOT_FOUND); } async addAvatar(userId: number, fileData: LocalFileDto) { const avatar = await this.localFilesService.saveLocalFileData(fileData); await this.usersRepository.update(userId, { avatarId: avatar.id }) } // ... } |
Solving the issue using forward referencing
In our case, the LocalFilesService needs the UsersService and the other way around. Let’s look into how our modules look so far.
localFiles.module.ts
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import { Module } from '@nestjs/common'; import { TypeOrmModule } from '@nestjs/typeorm'; import { ConfigModule } from '@nestjs/config'; import LocalFile from './localFile.entity'; import LocalFilesService from './localFiles.service'; import LocalFilesController from './localFiles.controller'; import { UsersModule } from '../users/users.module'; @Module({ imports: [ TypeOrmModule.forFeature([LocalFile]), ConfigModule, UsersModule ], providers: [LocalFilesService], exports: [LocalFilesService], controllers: [LocalFilesController] }) export class LocalFilesModule {} |
users.module.ts
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import { Module } from '@nestjs/common'; import { UsersService } from './users.service'; import { TypeOrmModule } from '@nestjs/typeorm'; import User from './user.entity'; import { UsersController } from './users.controller'; import { ConfigModule } from '@nestjs/config'; import { LocalFilesModule } from '../localFiles/localFiles.module'; @Module({ imports: [ TypeOrmModule.forFeature([User]), ConfigModule, LocalFilesModule, // ... ], providers: [UsersService], exports: [UsersService], controllers: [UsersController] }) export class UsersModule {} |
Above, we see that LocalFilesModule imports the UsersModule and vice versa. Running the application with the above configuration causes an error, unfortunately.
[ExceptionHandler] Nest cannot create the LocalFilesModule instance.
The module at index [2] of the LocalFilesModule “imports” array is undefined.Potential causes:
– A circular dependency between modules. Use forwardRef() to avoid it. Read more: https://docs.nestjs.com/fundamentals/circular-dependency
– The module at index [2] is of type “undefined”. Check your import statements and the type of the module.Scope [AppModule -> PostsModule -> UsersModule]
Error: Nest cannot create the LocalFilesModule instance.
The module at index [2] of the LocalFilesModule “imports” array is undefined.
A workaround for the above is to use forward referencing. Thanks to it, we can refer to a module before NestJS initializes it. To do that, we need to use the forwardRef function.
localFiles.module.ts
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import { Module, forwardRef } from '@nestjs/common'; import { TypeOrmModule } from '@nestjs/typeorm'; import { ConfigModule } from '@nestjs/config'; import LocalFile from './localFile.entity'; import LocalFilesService from './localFiles.service'; import LocalFilesController from './localFiles.controller'; import { UsersModule } from '../users/users.module'; @Module({ imports: [ TypeOrmModule.forFeature([LocalFile]), ConfigModule, forwardRef(() => UsersModule), ], providers: [LocalFilesService], exports: [LocalFilesService], controllers: [LocalFilesController] }) export class LocalFilesModule {} |
users.module.ts
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import { Module, forwardRef } from '@nestjs/common'; import { UsersService } from './users.service'; import { TypeOrmModule } from '@nestjs/typeorm'; import User from './user.entity'; import { UsersController } from './users.controller'; import { ConfigModule } from '@nestjs/config'; import { LocalFilesModule } from '../localFiles/localFiles.module'; @Module({ imports: [ TypeOrmModule.forFeature([User]), ConfigModule, forwardRef(() => LocalFilesModule), // ... ], providers: [UsersService], exports: [UsersService], controllers: [UsersController] }) export class UsersModule {} |
Doing the above solves the issue of circular dependencies between our modules. Unfortunately, we still need to fix the problem for services. We need to use the forwardRef function and the @Inject() decorator to do that.
localFiles.service.ts
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import { forwardRef, Inject, Injectable } from '@nestjs/common'; import { InjectRepository } from '@nestjs/typeorm'; import { Repository } from 'typeorm'; import LocalFile from './localFile.entity'; import { UsersService } from '../users/users.service'; @Injectable() class LocalFilesService { constructor( @InjectRepository(LocalFile) private localFilesRepository: Repository<LocalFile>, @Inject(forwardRef(() => UsersService)) private usersService: UsersService ) {} // ... } export default LocalFilesService; |
users.service.ts
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import { forwardRef, Inject, Injectable, } from '@nestjs/common'; import { InjectRepository } from '@nestjs/typeorm'; import { Repository } from 'typeorm'; import User from './user.entity'; import LocalFilesService from '../localFiles/localFiles.service'; @Injectable() export class UsersService { constructor( @InjectRepository(User) private usersRepository: Repository<User>, @Inject(forwardRef(() => LocalFilesService)) private localFilesService: LocalFilesService ) {} // ... } |
Doing all of the above causes our services to function correctly despite the circular dependencies.
Circular dependencies between TypeORM entities
We might also run into issues with circular dependencies with TypeORM entities. For example, this might happen when dealing with relationships.
If you want to know more about relationships with TypeORM and NestJS, check out API with NestJS #7. Creating relationships with Postgres and TypeORM
Fortunately, people noticed this problem, and there is a solution. For a whole discussion, check out this issue on GitHub.
Avoiding circular dependencies in our architecture
Unfortunately, having circular dependencies in our modules is often a sign of a design worth improving. In our case, we violate the single responsibility principle of SOLID. Our LocalFilesService and UsersService are responsible for multiple functionalities.
If you want to know more about SOLID, check out Applying SOLID principles to your TypeScript code
We can create a service that encapsulates the functionalities that would otherwise cause the circular dependency issue.
userAvatars.service.ts
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import { Injectable } from '@nestjs/common'; import { UsersService } from '../users/users.service'; import LocalFilesService from '../localFiles/localFiles.service'; @Injectable() class UserAvatarsService { constructor( private localFilesService: LocalFilesService, private usersService: UsersService ) {} async getUserAvatar(userId: number) { const user = await this.usersService.getById(userId); return this.localFilesService.getFileById(user.avatarId); } async addAvatar(userId: number, fileData: LocalFileDto) { const avatar = await this.localFilesService.saveLocalFileData(fileData); await this.usersService.updateUser(userId, { avatarId: avatar.id }) } } export default UserAvatarsService; |
We can now use the above service straight in our UsersController or create a brand new controller just for the new service.
users.controller.ts
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import { BadRequestException, Controller, Post, Req, UploadedFile, UseGuards, UseInterceptors } from '@nestjs/common'; import JwtAuthenticationGuard from '../authentication/jwt-authentication.guard'; import RequestWithUser from '../authentication/requestWithUser.interface'; import { Express } from 'express'; import LocalFilesInterceptor from '../localFiles/localFiles.interceptor'; import { ApiBody, ApiConsumes } from '@nestjs/swagger'; import FileUploadDto from './dto/fileUpload.dto'; import UserAvatarsService from '../userAvatars/userAvatars.service'; @Controller('users') export class UsersController { constructor( private readonly userAvatarsService: UserAvatarsService ) {} @Post('avatar') @UseGuards(JwtAuthenticationGuard) @UseInterceptors(LocalFilesInterceptor({ fieldName: 'file', path: '/avatars', fileFilter: (request, file, callback) => { if (!file.mimetype.includes('image')) { return callback(new BadRequestException('Provide a valid image'), false); } callback(null, true); }, limits: { fileSize: Math.pow(1024, 2) // 1MB } })) @ApiConsumes('multipart/form-data') @ApiBody({ description: 'A new avatar for the user', type: FileUploadDto, }) async addAvatar(@Req() request: RequestWithUser, @UploadedFile() file: Express.Multer.File) { return this.userAvatarsService.addAvatar(request.user.id, { path: file.path, filename: file.originalname, mimetype: file.mimetype }); } } |
Summary
In this article, we’ve looked into the issue of circular dependencies in the context of Node.js and NestJS. We’ve learned how Node.js deals with circular dependencies and how it can lead to problems that might be difficult to predict. We’ve also dealt with circular dependencies across NestJS using forward referencing. Since that is just a workaround and circular dependencies can signify a lacking design, we rewrote our code to eliminate it. That is usually the best approach, and we should avoid introducing circular dependencies to our architecture.
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