Use a Dependency Map for Dependency Mapping. Connect and share knowledge within a single location that is structured and easy to search.
However, you almost always inject services into application classes using Angular dependency injection and you should have tests that reflect that usage pattern. How to encourage melee combat when ranged is a stronger option, Blondie's Heart of Glass shimmering cascade effect. As I mentioned in a previous article, tight coupling is against the SOLID principles and we should endeavor to avoid it. Built on Forem the open source software that powers DEV and other inclusive communities. Initializing UserRepository in constructor has also another drawback. Whether or not the minor inconvenience of token-based dependency injection justifies this usage of abstract classes is a separate question. be paid a fee by the merchant. Because there are no simple solutions, and because many dependency-resolution frameworks try to solve the problem in different ways, this situation is often called "dependency hell". The FileService needs the UserService injected as a dependency to be able to fetch a user. Updated on Feb 18, This article was also posted on eftech.com. What's the difference between the Dependency Injection and Service Locator patterns? If you are needing the AService in another module, you should add the AService to the AModule 's exports array, and add AModule to the new module's imports array. Rather than just presenting the workaround NestJS provides, I will be walking us through how to avoid circular dependencies by rethinking how we couple dependencies, which will be helpful for better architecture in our backend code. A seemingly common complaint regarding NestJS and TypeScript is the absence of interfaces in runtime code (since interfaces are removed during transpilation). Well, NestJS has several ways to configure our dependencies and since were using UserRepository as TypeScript interface we have only one way to define our dependency non-class-based provider tokens: We defined AppModule with two providers/dependencies and some of them may depend on each other, in our case UserService is expected to get UserRepository implementation. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Before we talk about circular dependencies (and how to avoid them) in NestJS, let us first discuss how the NestJS dependency injection system works. Lets depict what we have done, it allows to get intuitive grasp of total picture and in which direction were trying to move: But in writhing test we created mocked version of UserRepository, but who should be responsible for managing UserRepository in application? My favorite JavaScript plugins for Slider Animations, Module Federation Series Part 1: A Little in-depth, The New React Document: Dont Abuse Effect, Spotify OAuth2 Authentication in a NestJS Application, Difference Between Middleware, Interceptor, and Filter in NestJS (2022), NestJS: Use a solo @injectable class as a singleton Provider, Unit testing TypeScript with Jest: Part One, NestJS DI Decoupling Services with Interfaces.
It will become hidden in your post, but will still be visible via the comment's permalink.
That might take up to a minute. Of course, the first which may come in mind is just change it in constructor: But lets imagine, that our UserRepository is used for other services as well, for example in ProfileService. LogRocket is a frontend application monitoring solution that lets you replay problems as if they happened in your own browser.
Issue I have created a custom ValidationFn in angular. If you click a merchant link and buy a product or service on their website, we This idea is not new and Composer is strongly inspired by node's npmand ruby's bundler.
We have to use this function on both sides of the circular reference. In general, nest automatically performs dependency injection during bootup, but this isn't happening while running unit-test and giving me the following error: Nest can't resolve dependencies of the AppService (?). How to add dax to pareto charting in powerbi? 9:55 AM How do I call 2 API in parallel and the third right after that in RXJS. With you every step of your journey.
This Answer collected from stackoverflow and tested by AngularFix community admins, is licensed under, Nestjs Dependency Injection and DDD / Clean Architecture, resolve dependency by the interface in NestJS, How to fix Angular issue: Cannot read properties of null (reading 'cannotContainSpace'). Find centralized, trusted content and collaborate around the technologies you use most. Inversion of Control vs Dependency Injection. The UserService is also updated as follows: We have a circular dependency in this case, as both UserService and FileService depend on each other (UserService FileService UserService). A forward reference allows Nest to reference classes that have not yet been defined by using the forwardRef() utility function.
To break it down Error: Nest can't resolve dependencies of the AService (?). Pay attention, that in listing 7, UserService set up in container as a dependency in a different way. "Selected/commanded," "indicated," what's the third word?
The benefits here that we just implement out components without any acknowledge about the concrete implementation and we need to work only against interfaces of any outside needed components. Why does hashing a password result in different hashes, each time? You also can use an abstract class instead of an interface or give both interface and implementation class a similar name (and use aliases in-place). You can read that Nest says Meaning Nest is looking at a module called AService. For example, we could have modified the UserService as follows: With this forward reference, the code will compile without errors. Lets use the below example for the implementation of the Property Injection or even it is called Setter Injection as value or dependency getting set in property. With the circular reference in place, the code will fail to compile.
It is not possible to resolve dependency by the interface in NestJS due to the language limitations/features (see structural vs nominal typing). All program managers must track the dependencies that exist between the projects which make up their program. What's the difference between iteration, sprint, and iteration?
The NestJS architecture favors creating the logic layer as dependencies (i.e., services) that can be consumed by the access layers (i.e., controllers). TypeScript here is just like a syntax sugar which make feel us more confident about what we writing and fix a lot of bugs before runtime. The Dependency Inversion principle tells us that the most flexible system are those in which source code dependencies refer only to abstractions, not concrete implementation. I'm experimenting with Nestjs by trying to implement a clean-architecture structure and I'd like to validate my solution because I'm not sure I understand the best way to do it. How would we create unit test for UserService?
In addition to logging Redux actions and state, LogRocket records console logs, JavaScript errors, stacktraces, network requests/responses with headers + bodies, browser metadata, and custom logs. So for example rather than the caller calling the method.
Can climbing up a tree prevent a creature from being targeted with Magic Missile? Visit the Dependency Injection chapter to learn more about it. First, you need to instal the typegraphql-nestjs module along with @nestjs/graphql: If you haven't installed it yet, it's time to add type-graphql into the project: How to use? For example, the UserModule is defined as follows: In a normal mode of execution, when an enquirer asks for a dependency, the injector checks the container to see if an object of that dependency has been cached previously. Do you need test for angular dependency injection? Lets have a look where we would need to apply this pattern and how it may be useful. The collective set of dependencies that must be resolved is typically referred to as a dependency tree, dependency graph, or object graph. Once unpublished, all posts by ef will become hidden and only accessible to themselves. 2021 FaqCode4U.com. The NestJS dependency injector will check for the requested dependency in a container, where it stores references to providers defined in the NestJS project. We will explore those differences a little bit later comparing how DI implemented in both Spring framework (Java) and NestJS (NodeJS). DEV Community 2016 - 2022. When you declare a module, you have to specify the providers that should be available to the module, except in cases where the provider is a global provider. How can i stream my twitch stream on my xbox? The youth dependency ratio includes those only under 15, and the elderly dependency ratio focuses on those over 64. Is ioc and dependency injection the same thing? What is dependency injection and what are advantages? In this article, we will be learning about circular dependencies in NestJS, why they arise, and how we can avoid them. clean-architecture, dependency-injection, domain-driven-design, nestjs, typescript But, you also can use class itself, or its name as a string literal, so you don't need to mention it during injection in, say, dependant's constructor. In my case I am using the postcss-loader which requires postcss, that requires autoprefixer which requires caniuse-lite as a dependency. When we defined UserRepository as TypeScript interface we need to know that it will be erased in transpilation phase and wont be available in runtime, its the main difference between statically typed languages and dynamically typed ones. What's the difference between expo cli and expo client? To learn more, see our tips on writing great answers. DEV Community A constructive and inclusive social network for software developers. We also learned how we can avoid circular dependencies in NestJS and why we should always try to avoid it. One of the beauties of NestJS is that it allows us to separate concerns within our applications. We can remove the circular dependency easily in this example. Hopefully, you now know how to work around it in case it cant be avoided using forward references. The UserService doesnt need to depend on FileService anymore, as you can see here: Similarly, FileService doesnt need to know a thing about UserService: The relationship between the three services can now be represented as follows: As you can see from the diagram, there is no circular reference among the services. Is the caniuse-lite dependency an outdated dependency?
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Right now in any time when we would like to change one implementation into another we just need to make changes in one places and NestJS just propagate it across all components of application. Posted on May 18, 2021 First of all, User class entity should be defined with all necessary properties (fields). The objects themselves do not know that they are managed by a container and know nothing about the container. By default it does not install anything globally. They simply represent the general idea of modules in programming, which refers to how we organize code. I had no idea that we were able to implement abstract classes instead of extending them. One of the common problems encountered in this regard is circular dependencies. It will look like that: I would also recommend you to review the following links: A new tech publication by Start it up (https://medium.com/swlh). Please make sure that the argument CACHE_MANAGER at index [0] is available in the RootTestModule context. The display of third-party trademarks and trade names on this site does not The container resolves ILogger by taking advantage of (generic) open types, eliminating the need to register every (generic) constructed type. Actually in a real project it may look like that: The larger app the higher probability that our UserRepository is a dependency for N services and in this case with our naive way we would need to change in each service implementation of UserRepository. Still, manually injecting tokens like this can be cumbersome and conceptually unsatisfying. error thrown when using angular cdk virtual scroller, Property does not exist on type 'IntrinsicAttributes' with useFormContext and custom tag, TypeError: Cannot set properties of undefined (setting 'object'), Angular web components with custom elements error, How to convert date into this 'yyyy-MM-dd' format in angular 2, 100% working solution for TypeError: Cannot read properties of null (reading 'classList') React. If you're feeling lazy, though, this is a convenient option! Error trying to diff '[object Object]'. Please note that the example is almost pseudo-code and a lot of types are missing or generic because they're not the focus of the discussion. NestJS code will not even compile if there is an unresolved circular dependency. Here is my codebase. 
Is it patent infringement to produce patented goods but take no compensation? What is "not assignable to parameter of type never" error in TypeScript? How to avoid dependency injection in nestjs api? In programming, a circular dependency occurs when two or more modules (or classes), directly or indirectly depend on one other. How is robot arm control using labview and arm? Examples include public pensions, schooling, or other forms of social security. And, if you are using an interface to define a (type of) dependency, then you have to use string tokens. Identifying a novel about floating islands, dragons, airships and a mysterious machine, Grep excluding line that ends in 0, but not 10, 100 etc, Proof that When all the sides of two triangles are congruent, the angles of those triangles must also be congruent (Side-Side-Side Congruence). 465), Design patterns for asynchronous API communication. Is the fact that ZFC implies that 1+1=2 an absolute truth? This limitation prevents the use of constructor-based dependency injection and instead necessitates use of the @Inject decorator. Templates let you quickly answer FAQs or store snippets for re-use. What was the doctrine of the oneness doctrine? So fa Issue I want to convert current data into 'yyyy-MM-dd' format in .ts file Issue I am having this header which on scroll, I want to change the background to a differ Issue I want to make 2 API calls in Parallel and then the third immediately after that. What are the purpose of the extra diodes in this peak detector circuit (LM1815)? The dependency issue arises when several packages have dependencies on the same shared packages or libraries, but they depend on different and incompatible versions of the shared packages. Once unpublished, this post will become invisible to the public Only arrays and iterables are allowed in Angular-11 Application, Why is @angular/core/core has no exported member 'FactoryDeclaration'. The dependency ratio is the percentage of children and those over 64 years old, compared to the people who are of working age. So let's discuss one by one. After that it will work right. UserService is defined as a JS class and therefore this information is available in runtime, therefore its not difficult for lookup mechanism to find needed dependency by class, framework just uses JS operator instanceOf. Why are dependency conflicts called " dependency hell "? caniuse-lite is outdated PanJiaChen/vue-element-admin#1961 @Dan503 thank you ,I got resolved this problem! The gitmojis are published on the following package in order to be used as a dependency . Making statements based on opinion; back them up with references or personal experience. But before divining deeper just remind you one thing which we all need to keep in mind. The ProfilePictureService will have its own module defined as follows: Note that this module imports both the FileModule and the UserModule. In property injection, we need to pass object of the dependent class through a public property of the client class. The circular reference we have can also be represented as the following: To break the cycle, we can extract the common features from both services into a new service that depends on both services. Lets inject this dependency in UserService then: First of all, we put decorator @Injectable, which say that this component is gonna to be used as dependency in application, and in constructor we used @Inject decorator and passes which exact dependency were interested in, lookup mechanism by Symbol or it may be any unique string without any problem may match needed component associated and registered in container. How is constructor injection used in dependency injection? Note that the concept of circular dependency is not unique to NestJS, and in fact, the modules used here as example dont even have to be NestJS modules. IOC is a concept where the flow of application is inverted. Quote from the NestJS docs on this topic: Instead of a custom token, we have used the ConfigService class, and therefore we have overridden the default implementation. The easiest way Ive found to do this is by using a Dependency Map. Starting from my domain logic, I might want to implement it in a class like the following: Here I need to get access to the profileRepository, but following the principles of the clean architecture, I don't want to be bothered with the implementation just now so I write an interface for it: Then I inject the dependency in the ProfileDomainEntity constructor and I make sure it's gonna follow the expected interface: And then I create a simple in memory implementation that let me run the code: Now it's time to wiring everything together by using a module: The problem here is that obviously ProfileRepository implements IProfilesRepository but it's not IProfilesRepository and therefore, as far as I understand, the token is different and Nest is not able to resolve the dependency. It is even better if the objects use dependency injection for their dependencies, but that's not a prerequisite. Construction injection is a type of Dependency Injection where dependencies are provided through a constructor. @ntegral/nestjs-sendgrid implements a module, SendGridModule, which when imported into your nestjs project provides a SendGrid client to any class that injects it. Lets refactor UserService and decouple it with UserRepository implementation, we just ask to initialize needed UserRepository outside of UserService and it will be passed in constructor: This straightforward step to refactor brings one benefit for test, lets have a look: Since we decoupled UserService and UserRepository implementation, right now we dont take care in unit test which implementation is used, we just need to follow UserRepository interface. Reduced Dependency Carrying. Suppose: You have a project that depends on a number of libraries. Based on your error, you have AService in an imports array somewhere, which is not something you do in NestJS.
However, you almost always inject services into application classes using Angular dependency injection and you should have tests that reflect that usage pattern. How to encourage melee combat when ranged is a stronger option, Blondie's Heart of Glass shimmering cascade effect. As I mentioned in a previous article, tight coupling is against the SOLID principles and we should endeavor to avoid it. Built on Forem the open source software that powers DEV and other inclusive communities. Initializing UserRepository in constructor has also another drawback. Whether or not the minor inconvenience of token-based dependency injection justifies this usage of abstract classes is a separate question. be paid a fee by the merchant. Because there are no simple solutions, and because many dependency-resolution frameworks try to solve the problem in different ways, this situation is often called "dependency hell". The FileService needs the UserService injected as a dependency to be able to fetch a user. Updated on Feb 18, This article was also posted on eftech.com. What's the difference between the Dependency Injection and Service Locator patterns? If you are needing the AService in another module, you should add the AService to the AModule 's exports array, and add AModule to the new module's imports array. Rather than just presenting the workaround NestJS provides, I will be walking us through how to avoid circular dependencies by rethinking how we couple dependencies, which will be helpful for better architecture in our backend code. A seemingly common complaint regarding NestJS and TypeScript is the absence of interfaces in runtime code (since interfaces are removed during transpilation). Well, NestJS has several ways to configure our dependencies and since were using UserRepository as TypeScript interface we have only one way to define our dependency non-class-based provider tokens: We defined AppModule with two providers/dependencies and some of them may depend on each other, in our case UserService is expected to get UserRepository implementation. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Before we talk about circular dependencies (and how to avoid them) in NestJS, let us first discuss how the NestJS dependency injection system works. Lets depict what we have done, it allows to get intuitive grasp of total picture and in which direction were trying to move: But in writhing test we created mocked version of UserRepository, but who should be responsible for managing UserRepository in application? My favorite JavaScript plugins for Slider Animations, Module Federation Series Part 1: A Little in-depth, The New React Document: Dont Abuse Effect, Spotify OAuth2 Authentication in a NestJS Application, Difference Between Middleware, Interceptor, and Filter in NestJS (2022), NestJS: Use a solo @injectable class as a singleton Provider, Unit testing TypeScript with Jest: Part One, NestJS DI Decoupling Services with Interfaces.
It will become hidden in your post, but will still be visible via the comment's permalink.
That might take up to a minute. Of course, the first which may come in mind is just change it in constructor: But lets imagine, that our UserRepository is used for other services as well, for example in ProfileService. LogRocket is a frontend application monitoring solution that lets you replay problems as if they happened in your own browser.
Issue I have created a custom ValidationFn in angular. If you click a merchant link and buy a product or service on their website, we This idea is not new and Composer is strongly inspired by node's npmand ruby's bundler. We have to use this function on both sides of the circular reference. In general, nest automatically performs dependency injection during bootup, but this isn't happening while running unit-test and giving me the following error: Nest can't resolve dependencies of the AppService (?). How to add dax to pareto charting in powerbi? 9:55 AM How do I call 2 API in parallel and the third right after that in RXJS. With you every step of your journey.
This Answer collected from stackoverflow and tested by AngularFix community admins, is licensed under, Nestjs Dependency Injection and DDD / Clean Architecture, resolve dependency by the interface in NestJS, How to fix Angular issue: Cannot read properties of null (reading 'cannotContainSpace'). Find centralized, trusted content and collaborate around the technologies you use most. Inversion of Control vs Dependency Injection. The UserService is also updated as follows: We have a circular dependency in this case, as both UserService and FileService depend on each other (UserService FileService UserService). A forward reference allows Nest to reference classes that have not yet been defined by using the forwardRef() utility function.
To break it down Error: Nest can't resolve dependencies of the AService (?). Pay attention, that in listing 7, UserService set up in container as a dependency in a different way. "Selected/commanded," "indicated," what's the third word?
The benefits here that we just implement out components without any acknowledge about the concrete implementation and we need to work only against interfaces of any outside needed components. Why does hashing a password result in different hashes, each time? You also can use an abstract class instead of an interface or give both interface and implementation class a similar name (and use aliases in-place). You can read that Nest says Meaning Nest is looking at a module called AService. For example, we could have modified the UserService as follows: With this forward reference, the code will compile without errors. Lets use the below example for the implementation of the Property Injection or even it is called Setter Injection as value or dependency getting set in property. With the circular reference in place, the code will fail to compile.
It is not possible to resolve dependency by the interface in NestJS due to the language limitations/features (see structural vs nominal typing). All program managers must track the dependencies that exist between the projects which make up their program. What's the difference between iteration, sprint, and iteration?
The NestJS architecture favors creating the logic layer as dependencies (i.e., services) that can be consumed by the access layers (i.e., controllers). TypeScript here is just like a syntax sugar which make feel us more confident about what we writing and fix a lot of bugs before runtime. The Dependency Inversion principle tells us that the most flexible system are those in which source code dependencies refer only to abstractions, not concrete implementation. I'm experimenting with Nestjs by trying to implement a clean-architecture structure and I'd like to validate my solution because I'm not sure I understand the best way to do it. How would we create unit test for UserService?
In addition to logging Redux actions and state, LogRocket records console logs, JavaScript errors, stacktraces, network requests/responses with headers + bodies, browser metadata, and custom logs. So for example rather than the caller calling the method.
Can climbing up a tree prevent a creature from being targeted with Magic Missile? Visit the Dependency Injection chapter to learn more about it. First, you need to instal the typegraphql-nestjs module along with @nestjs/graphql: If you haven't installed it yet, it's time to add type-graphql into the project: How to use? For example, the UserModule is defined as follows: In a normal mode of execution, when an enquirer asks for a dependency, the injector checks the container to see if an object of that dependency has been cached previously. Do you need test for angular dependency injection? Lets have a look where we would need to apply this pattern and how it may be useful. The collective set of dependencies that must be resolved is typically referred to as a dependency tree, dependency graph, or object graph. Once unpublished, all posts by ef will become hidden and only accessible to themselves. 2021 FaqCode4U.com. The NestJS dependency injector will check for the requested dependency in a container, where it stores references to providers defined in the NestJS project. We will explore those differences a little bit later comparing how DI implemented in both Spring framework (Java) and NestJS (NodeJS). DEV Community 2016 - 2022. When you declare a module, you have to specify the providers that should be available to the module, except in cases where the provider is a global provider. How can i stream my twitch stream on my xbox? The youth dependency ratio includes those only under 15, and the elderly dependency ratio focuses on those over 64. Is ioc and dependency injection the same thing? What is dependency injection and what are advantages? In this article, we will be learning about circular dependencies in NestJS, why they arise, and how we can avoid them. clean-architecture, dependency-injection, domain-driven-design, nestjs, typescript But, you also can use class itself, or its name as a string literal, so you don't need to mention it during injection in, say, dependant's constructor. In my case I am using the postcss-loader which requires postcss, that requires autoprefixer which requires caniuse-lite as a dependency. When we defined UserRepository as TypeScript interface we need to know that it will be erased in transpilation phase and wont be available in runtime, its the main difference between statically typed languages and dynamically typed ones. What's the difference between expo cli and expo client? To learn more, see our tips on writing great answers. DEV Community A constructive and inclusive social network for software developers. We also learned how we can avoid circular dependencies in NestJS and why we should always try to avoid it. One of the beauties of NestJS is that it allows us to separate concerns within our applications. We can remove the circular dependency easily in this example. Hopefully, you now know how to work around it in case it cant be avoided using forward references. The UserService doesnt need to depend on FileService anymore, as you can see here: Similarly, FileService doesnt need to know a thing about UserService: The relationship between the three services can now be represented as follows: As you can see from the diagram, there is no circular reference among the services. Is the caniuse-lite dependency an outdated dependency?
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Right now in any time when we would like to change one implementation into another we just need to make changes in one places and NestJS just propagate it across all components of application. Posted on May 18, 2021 First of all, User class entity should be defined with all necessary properties (fields). The objects themselves do not know that they are managed by a container and know nothing about the container. By default it does not install anything globally. They simply represent the general idea of modules in programming, which refers to how we organize code. I had no idea that we were able to implement abstract classes instead of extending them. One of the common problems encountered in this regard is circular dependencies. It will look like that: I would also recommend you to review the following links: A new tech publication by Start it up (https://medium.com/swlh). Please make sure that the argument CACHE_MANAGER at index [0] is available in the RootTestModule context. The display of third-party trademarks and trade names on this site does not The container resolves ILogger
Is it patent infringement to produce patented goods but take no compensation? What is "not assignable to parameter of type never" error in TypeScript? How to avoid dependency injection in nestjs api? In programming, a circular dependency occurs when two or more modules (or classes), directly or indirectly depend on one other. How is robot arm control using labview and arm? Examples include public pensions, schooling, or other forms of social security. And, if you are using an interface to define a (type of) dependency, then you have to use string tokens. Identifying a novel about floating islands, dragons, airships and a mysterious machine, Grep excluding line that ends in 0, but not 10, 100 etc, Proof that When all the sides of two triangles are congruent, the angles of those triangles must also be congruent (Side-Side-Side Congruence). 465), Design patterns for asynchronous API communication. Is the fact that ZFC implies that 1+1=2 an absolute truth? This limitation prevents the use of constructor-based dependency injection and instead necessitates use of the @Inject decorator. Templates let you quickly answer FAQs or store snippets for re-use. What was the doctrine of the oneness doctrine? So fa Issue I want to convert current data into 'yyyy-MM-dd' format in .ts file Issue I am having this header which on scroll, I want to change the background to a differ Issue I want to make 2 API calls in Parallel and then the third immediately after that. What are the purpose of the extra diodes in this peak detector circuit (LM1815)? The dependency issue arises when several packages have dependencies on the same shared packages or libraries, but they depend on different and incompatible versions of the shared packages. Once unpublished, this post will become invisible to the public Only arrays and iterables are allowed in Angular-11 Application, Why is @angular/core/core has no exported member 'FactoryDeclaration'. The dependency ratio is the percentage of children and those over 64 years old, compared to the people who are of working age. So let's discuss one by one. After that it will work right. UserService is defined as a JS class and therefore this information is available in runtime, therefore its not difficult for lookup mechanism to find needed dependency by class, framework just uses JS operator instanceOf. Why are dependency conflicts called " dependency hell "? caniuse-lite is outdated PanJiaChen/vue-element-admin#1961 @Dan503 thank you ,I got resolved this problem! The gitmojis are published on the following package in order to be used as a dependency . Making statements based on opinion; back them up with references or personal experience. But before divining deeper just remind you one thing which we all need to keep in mind. The ProfilePictureService will have its own module defined as follows: Note that this module imports both the FileModule and the UserModule. In property injection, we need to pass object of the dependent class through a public property of the client class. The circular reference we have can also be represented as the following: To break the cycle, we can extract the common features from both services into a new service that depends on both services. Lets inject this dependency in UserService then: First of all, we put decorator @Injectable, which say that this component is gonna to be used as dependency in application, and in constructor we used @Inject decorator and passes which exact dependency were interested in, lookup mechanism by Symbol or it may be any unique string without any problem may match needed component associated and registered in container. How is constructor injection used in dependency injection? Note that the concept of circular dependency is not unique to NestJS, and in fact, the modules used here as example dont even have to be NestJS modules. IOC is a concept where the flow of application is inverted. Quote from the NestJS docs on this topic: Instead of a custom token, we have used the ConfigService class, and therefore we have overridden the default implementation. The easiest way Ive found to do this is by using a Dependency Map. Starting from my domain logic, I might want to implement it in a class like the following: Here I need to get access to the profileRepository, but following the principles of the clean architecture, I don't want to be bothered with the implementation just now so I write an interface for it: Then I inject the dependency in the ProfileDomainEntity constructor and I make sure it's gonna follow the expected interface: And then I create a simple in memory implementation that let me run the code: Now it's time to wiring everything together by using a module: The problem here is that obviously ProfileRepository implements IProfilesRepository but it's not IProfilesRepository and therefore, as far as I understand, the token is different and Nest is not able to resolve the dependency. It is even better if the objects use dependency injection for their dependencies, but that's not a prerequisite. Construction injection is a type of Dependency Injection where dependencies are provided through a constructor. @ntegral/nestjs-sendgrid implements a module, SendGridModule, which when imported into your nestjs project provides a SendGrid client to any class that injects it. Lets refactor UserService and decouple it with UserRepository implementation, we just ask to initialize needed UserRepository outside of UserService and it will be passed in constructor: This straightforward step to refactor brings one benefit for test, lets have a look: Since we decoupled UserService and UserRepository implementation, right now we dont take care in unit test which implementation is used, we just need to follow UserRepository interface. Reduced Dependency Carrying. Suppose: You have a project that depends on a number of libraries. Based on your error, you have AService in an imports array somewhere, which is not something you do in NestJS.