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Graph/f56c852e-840a-490a-9d80-d2e1aa4d5e60

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Dependency Injection

f56c852e-840a-490a-9d80-d2e1aa4d5e60

Dependency Injection

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Updated4/30/2026

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40 linked nodes

RELATES_TOProblem

I want to use this CRUD service when my class is serialized — I have a CRUD service in Spring Boot, and I'm using a custom serializer with a class that extends `JsonSerializer`. Tension: I've tried several approaches without success.

PERTAIN_TOProblem

I have never tried to use a decorator on an asynchronous function so I am confused — @review_router.get("/review") @admin_required async def get_review():. Tension: if it is going to affect asynchronous tasks. Outcome: Yes, it's Ok to use such decorators.

PERTAIN_TOSolution

Yes, it's Ok to use such decorators. — @review_router.get("/review") @admin_required async def get_review():. Tension: This use-case is covered by tests in FastAPI repo. Outcome: This use-case is covered by tests in FastAPI repo: https://github.com/fastapi/fastapi/blob/6513d4daa16a536d17743de6a292f49bd06388a4/tests/test_dependency_wrapped.py#L183-L200.

PERTAIN_TOSolution

The yielded value is what is injected into path operations and other dependencies — async def get_db():.

PERTAIN_TOProblem

the background job never runs — my `BackgroundTasks` only execute when declared inside an async dependency. Tension: No exception is raised, the route returns normally. Outcome: If I move the `bg.add_task()` call into the route itself, it works as expected.

PERTAIN_TOSolution

Pass `BackgroundTasks` from the route into your dependency. — when declared inside an async dependency. Tension: the background job never runs. Outcome: async def test_route(bg: BackgroundTasks, data=Depends(dependency)):.

PERTAIN_TOProblem

Is there a way to pass an argument to a function defined within the `dependencies` argument — within the `dependencies` argument of, for instance, `app.get`. Tension: I really want to do is provide an argument to `verify_token`. Outcome: there isn't, what other options exist ?

PERTAIN_TOSolution

The easy way is to have the function return another function — `verify_token("red")` returns a callable with the right syntax and type annotations. Tension: FastAPI can use it as a dependency.

PERTAIN_TOProblem

it insists on actually using the real client which tries to really call a Qdrant server — write a unit for `/my_endpoint`.

PERTAIN_TOSolution

Move the initialization of `qdrant_client` into lifespan. Outcome: override using standard FastAPI mechanism.

PERTAIN_TOProblem

the first relationship is always automatically loaded although it shouldn't — using SQLAlchemy and Pydantic with a Postgres-Database. Tension: The second relationship works as expected. Outcome: I am going to have two different endpoints.

PERTAIN_TOSolution

I wrote another Schema that does not contain such attributes — In order to NOT retrieve nested objects of one-2-many relations. Tension: one that contains only basic attributes for a flat response. Outcome: one that contains the relationships.

PERTAIN_TOProblem

method object does not support the context manager protocol

PERTAIN_TOSolution

Use the db client itself and call self.db_client.session() inside the service

PERTAIN_TOProblem

The route responds with a 422 Unprocessable Entity status code. — if the function declares the input parameter with `Annotated` and `Depends`. Tension: I am unable to run the tests with `pytest`. Outcome: The Main issue remains unsolved.

PERTAIN_TOSolution

when I create the test client. Tension: The 'app' shortcut is now deprecated. Outcome: async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as async_test_client:.

PERTAIN_TOProblem

"type":"missing","loc":["query","name"]. Tension: The query will return None and FastApi will fail to validate that parameter is a Person object. Outcome: Any post request to the endpoint /post_with_dependency will indeed return a 422 Unprocessable Entity error.

PERTAIN_TOSolution

such a dependency could be to validate that the name attribute is a full name. Tension: the dependency in your example needs to return a Person object.

PERTAIN_TOSolution

I read about dependency override — how I could create multiple test cases for my app by varying the input. Tension: I am not sure if that is mandatory.

PERTAIN_TOProblem

Unable to inject and configure Aws\S3\S3Client as a Symfony service

PERTAIN_TOSolution

What you want to do is install some wrapper around AWS SDK — AWS SDK is not suitable for DI and Symfony services approach. Outcome: like AWS Service Provider for Symfony.

PERTAIN_TOSolution

I made a proxy object — using the magic method `__call` in order to forward any method call towards to actual S3. Tension: I failed. Outcome: Then upon services.yaml you can do.

PERTAIN_TORootCause

multi-tenant application using NestJS and Prisma. Tension: you need to create a dynamic DB instance based on each request. Outcome: Request provider is what you are looking for.

PERTAIN_TOProblem

I want to dynamically set the databaseUrl based on the subdomain from my Next.js frontend — I’m working on a multi-tenant application using NestJS and Prisma. Tension: I’m not sure how to proceed with dynamically setting the databaseUrl in Prisma. Outcome: I’ve created a middleware to extract the subdomain from the request.

PERTAIN_TOSolution

Request provider is what you are looking for — each request should only create one DB client instance. Tension: you will have to inject the DatabaseProvider and call getDbClient. Outcome: create a dynamic DB instance based on each request.

PERTAIN_TOSolution

Spring Boot 4 introduced some major changes where, by default, it uses Jackson 3 instead of Jackson 2. Outcome: making it a more suitable candidate over the no-arg counterpart.

PERTAIN_TOSolution

Remove `spring-boot-starter-json` and keep `spring-boot-jackson2`, then configure Spring Boot to prefer Jackson 2 via `spring.http.converters.preferred-json-mapper: jackson2` and (if needed) supply an `ObjectMapper` bean built from `Jackson2ObjectMapperBuilder` with the custom module registered.

PERTAIN_TOProblem

After migrating from field injection to constructor-based injection, Spring throws a BeanCreationException when instantiating `exampleCommand` because it cannot resolve a constructor parameter for the DTO passed via `beanFactory.getBean(Command.class, inputDto)`.

PERTAIN_TOSolution

Do not expect the DTO to be injected into the command via constructor autowiring; instead, configure the command as a plain class and inject a provider/factory (e.g., a bean or functional interface) that accepts the DTO, or otherwise supply the DTO through a non-autowired step/setter after bean creation.

PERTAIN_TOSolution

@ExtendWith({ MockitoExtension.class, ApplicationExtension.class }) — To use TestFX to test a JavaFX application. Tension: how do you do both at the same time? Outcome: it works for this case.

PERTAIN_TOProblem

I cannot inject a primitive (an int) due to `The injection point has non-proxyable dependencies` exception. — following this tutorial on how to use Jakarta CDI. Tension: Is that even possible to inject a primitive using WELD? Outcome: remove `@RequestScoped` annotation from producer method.

PERTAIN_TOSolution

The solution is remove `@RequestScoped` annotation from producer method. Outcome: remove `@RequestScoped` annotation from producer method.

PERTAIN_TOProblem

if the `userService` field is removed, the dependency is set to null, which causes a `NullPointerException` when the test runs — In my Spring Boot app, I have some tests that look like this. Tension: I don't need to mock or verify any `userService` methods, so IntelliJ marks this as an unused field.

PERTAIN_TOSolution

You could achieve this with constructor injection. — In your service, make sure the dependencies are injected using the constructor. Tension: what I'd prefer is to not have to declare this field at all. Outcome: private InviteService inviteService = new InviteService(emailSendingService, userService);.

PERTAIN_TOProblem

I want to use this CRUD service when my class is serialized — I have a CRUD service in Spring Boot, and I'm using a custom serializer with a class that extends `JsonSerializer`. Tension: I've tried several approaches without success.

PERTAIN_TOSolution

Usamos ApplicationContextProvider para obtener el servicio después de la inicialización de Spring — @PostConstruct public void init(). Outcome: this.customerUserServiceIMPL = ApplicationContextProvider.getBean(CustomerUserServiceIMPL.class);.

PERTAIN_TOProblem

A container entity needs to persist a List of objects whose types are subclasses of a common base class. Because the base is annotated with @MappedSuperclass, attempts to map the list using generics/relationship annotations fail.

PERTAIN_TOSolution

Make the common superclass an @Entity and use JPA inheritance (e.g., @Inheritance with JOINED/TABLE_PER_CLASS/SINGLE_TABLE) so the container can reference the entity type. Then map the collection as a relationship to the base entity type (or use an association table/discriminator via the chosen inheritance strategy), rather than storing IDs as a workaround.

PERTAIN_TOProblem

The `MdcConfig` fields are bound correctly, but `SomeClass` sees `mdcConfig` as null and/or its derived field `mdcAllowedItems` ends up null. Breakpoints show `MdcConfig` setters are called, yet `SomeClass` initialization reads before injection.

PERTAIN_TOSolution

Move initialization of `mdcAllowedItems` to `@PostConstruct`, or refactor to constructor injection (make `mdcConfig` final) and initialize `mdcAllowedItems` in the constructor after `mdcConfig` is injected.

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