React to FastAPI

The connection generator provides a way to quickly integrate your React website with your FastAPI backend. It sets up all necessary configuration for connecting to your FastAPI backends in a type-safe manner, including client and TanStack Query hooks generation, AWS IAM and Cognito authentication support and proper error handling.

Prerequisites

Before using this generator, ensure your React application has:

1. A main.tsx file that renders your application
2. A working FastAPI backend (generated using the FastAPI generator)
3. Cognito Auth added via the ts#website#auth generator if connecting an API which uses Cognito or IAM auth

Example of required main.tsx structure

import { StrictMode } from 'react';
import * as ReactDOM from 'react-dom/client';
import App from './app/app';

const root = ReactDOM.createRoot(
  document.getElementById('root') as HTMLElement,
);
root.render(
  <StrictMode>
    <App />
  </StrictMode>,
);

Usage

Run the Generator

CLI

pnpm

pnpm nx g @aws/nx-plugin:connection

yarn

yarn nx g @aws/nx-plugin:connection

npm

npx nx g @aws/nx-plugin:connection

bun

bunx nx g @aws/nx-plugin:connection

You can also perform a dry-run to see what files would be changed

pnpm

pnpm nx g @aws/nx-plugin:connection --dry-run

yarn

yarn nx g @aws/nx-plugin:connection --dry-run

npm

npx nx g @aws/nx-plugin:connection --dry-run

bun

bunx nx g @aws/nx-plugin:connection --dry-run

VSCode

1. Install the Nx Console VSCode Plugin if you haven't already
2. Open the Nx Console in VSCode
3. Click Generate (UI) in the "Common Nx Commands" section
4. Search for @aws/nx-plugin - connection
5. Fill in the required parameters
6. Click Generate

Options

Parameter	Type	Default	Description
sourceProject Required	string	-	The source project
targetProject Required	string	-	The target project to connect to
sourceComponent	string	-	The source component to connect from (component name, path relative to source project root, or generator id). Use '.' to explicitly select the project as the source.
targetComponent	string	-	The target component to connect to (component name, path relative to target project root, or generator id). Use '.' to explicitly select the project as the target.
preferInstallDependencies	boolean	true	Whether to prefer installing dependencies after the generator runs. Set to false to defer installing when batching multiple generators (an install still runs if needed so subsequent generators can compute the Nx project graph); install once at the end.

Generator Output

The generator will make changes to the following files in your FastAPI project:

• Directoryscripts

  • generate_open_api.py Add a script which generates an OpenAPI specification for your API
• project.json A new target is added to the build which invokes the above generate script

The generator will make changes to the following files in your React application:

• Directorysrc

  • Directorycomponents

    • <ApiName>Provider.tsx Provider for your API client
    • QueryClientProvider.tsx TanStack React Query client provider
  • Directoryhooks

    • use<ApiName>.tsx Add a hook for calling your API with state managed by TanStack Query
    • use<ApiName>Client.tsx Add a hook for instantiating the vanilla API client which can call your API.
    • useSigV4.tsx Add a hook for signing HTTP requests with SigV4 (if you selected IAM authentication)
• project.json A new target is added to the build which generates a type-safe client
• .gitignore The generated client files are ignored by default

The generator will also add Runtime Config to your website infrastructure if not present already, which ensures that the API URL for your FastAPI is available in the website and automatically configured by the use<ApiName>.tsx hook.

Code Generation

At build time, a type-safe client is generated from your FastAPI’s OpenAPI specification. This will add three new files to your React application:

• Directorysrc

  • Directorygenerated

    • Directory<ApiName>

      • types.gen.ts Generated types from the pydantic models defined in your FastAPI
      • client.gen.ts Type-safe client for calling your API
      • options-proxy.gen.ts Provides methods to create TanStack Query hooks options for interacting with your API using TanStack Query

Generated Client in Git

By default, the generated client is ignored from version control. If you would prefer to check it in, you can remove the entry from your React application’s .gitignore file, however note that any manual changes to the .gen.ts files will be overwritten when your project is built.

Using the Generated Code

The generated type-safe client can be used to call your FastAPI from your React application. It’s recommended to make use of the client via the TanStack Query hooks, but you can use the vanilla client if you prefer.

Regenerating Client Code

Whenever you make changes to your FastAPI, you need to rebuild your project in order for those changes to be reflected in the generated client. For example:

pnpm

pnpm build

yarn

yarn build

npm

npm run build

bun

bun build

Auto-Regeneration

If you’re actively working on both your React application and FastAPI together, use the React application’s dev target which will automatically regenerate the client whenever your API changes, as well as hot-reloading your website and local FastAPI server:

pnpm

pnpm nx dev <WebsiteProject>

yarn

yarn nx dev <WebsiteProject>

npm

npx nx dev <WebsiteProject>

bun

bunx nx dev <WebsiteProject>

For more fine-grained control, you can use the watch-generate:<ApiName>-client target for your React application to regenerate the client every time you make API changes:

pnpm

pnpm nx run <WebsiteProject>:"watch-generate:<ApiName>-client"

yarn

yarn nx run <WebsiteProject>:"watch-generate:<ApiName>-client"

npm

npx nx run <WebsiteProject>:"watch-generate:<ApiName>-client"

bun

bunx nx run <WebsiteProject>:"watch-generate:<ApiName>-client"

File Watcher Dependency

watch-generate:<ApiName>-client relies on the nx watch command, which requires the Nx Daemon to be running. Therefore if you have disabled the daemon, the client won’t automatically regenerate when making changes to your FastAPI.

Using the API Hook

The generator provides a use<ApiName> hook which you can use to call your API with TanStack Query.

Queries

You can use the queryOptions method to retrieve the options required for calling your API using TanStack Query’s useQuery hook:

import { useQuery } from '@tanstack/react-query';
import { useState, useEffect } from 'react';
import { useMyApi } from './hooks/useMyApi';

function MyComponent() {
  const api = useMyApi();
  const item = useQuery(api.getItem.queryOptions({ itemId: 'some-id' }));

  if (item.isLoading) return <div>Loading...</div>;
  if (item.isError) return <div>Error: {item.error.message}</div>;

  return <div>Item: {item.data.name}</div>;
}

Click here for an example using the vanilla client directly.

Mutations

The generated hooks include support for mutations using TanStack Query’s useMutation hook. This provides a clean way to handle create, update, and delete operations with loading states, error handling, and optimistic updates.

import { useMutation } from '@tanstack/react-query';
import { useMyApi } from './hooks/useMyApi';

function CreateItemForm() {
  const api = useMyApi();
  // Create a mutation using the generated mutation options
  const createItem = useMutation(api.createItem.mutationOptions());

  const handleSubmit = (e) => {
    e.preventDefault();
    createItem.mutate({ name: 'New Item', description: 'A new item' });
  };

  return (
    <form onSubmit={handleSubmit}>
      {/* Form fields */}
      <button
        type="submit"
        disabled={createItem.isPending}
      >
        {createItem.isPending ? 'Creating...' : 'Create Item'}
      </button>

      {createItem.isSuccess && (
        <div className="success">
          Item created with ID: {createItem.data.id}
        </div>
      )}

      {createItem.isError && (
        <div className="error">
          Error: {createItem.error.message}
        </div>
      )}
    </form>
  );
}

You can also add callbacks for different mutation states:

const createItem = useMutation({
  ...api.createItem.mutationOptions(),
  onSuccess: (data) => {
    // This will run when the mutation succeeds
    console.log('Item created:', data);
    // You can navigate to the new item
    navigate(`/items/${data.id}`);
  },
  onError: (error) => {
    // This will run when the mutation fails
    console.error('Failed to create item:', error);
  },
  onSettled: () => {
    // This will run when the mutation completes (success or error)
    // Good place to invalidate queries that might be affected
    queryClient.invalidateQueries({ queryKey: api.listItems.queryKey() });
  }
});

Click here for an example using the client directly.

File Uploads

For endpoints that accept a file upload, the generated client sends the request as FormData. Define an operation with a multipart/form-data body in your FastAPI, for example using UploadFile:

from fastapi import UploadFile

@app.post("/files")
async def upload_file(file: UploadFile, description: str = "") -> FileMetadata:
    contents = await file.read()
    ...

Binary fields are typed as Blob on the generated client, and other fields (such as description above) keep their modelled types. Pass a Blob or File — for example one obtained from an <input type="file">:

import { useMutation } from '@tanstack/react-query';
import { useMyApi } from './hooks/useMyApi';

function UploadForm() {
  const api = useMyApi();
  const uploadFile = useMutation(api.uploadFile.mutationOptions());

  const handleChange = (e: React.ChangeEvent<HTMLInputElement>) => {
    const file = e.target.files?.[0];
    if (file) {
      uploadFile.mutate({ file, description: file.name });
    }
  };

  return <input type="file" onChange={handleChange} />;
}

The client builds a FormData body and lets fetch set the Content-Type (including the multipart boundary) automatically.

Pagination with Infinite Queries

For endpoints that accept a cursor parameter as input, the generated hooks provide support for infinite queries using TanStack Query’s useInfiniteQuery hook. This makes it easy to implement “load more” or infinite scrolling functionality.

import { useInfiniteQuery } from '@tanstack/react-query';
import { useMyApi } from './hooks/useMyApi';

function ItemList() {
  const api = useMyApi();
  const items = useInfiniteQuery({
    ...api.listItems.infiniteQueryOptions({
      limit: 10, // Number of items per page
    }, {
      // Make sure you define a getNextPageParam function to return
      // the parameter that should be passed as the 'cursor' for the
      // next page
      getNextPageParam: (lastPage) =>
        lastPage.nextCursor || undefined
      }),
  });

  if (items.isLoading) {
    return <LoadingSpinner />;
  }

  if (items.isError) {
    return <ErrorMessage message={items.error.message} />;
  }

  return (
    <div>
      {/* Flatten the pages array to render all items */}
      <ul>
        {items.data.pages.flatMap(page =>
          page.items.map(item => (
            <li key={item.id}>{item.name}</li>
          ))
        )}
      </ul>

      <button
        onClick={() => items.fetchNextPage()}
        disabled={!items.hasNextPage || items.isFetchingNextPage}
      >
        {items.isFetchingNextPage
          ? 'Loading more...'
          : items.hasNextPage
          ? 'Load More'
          : 'No more items'}
      </button>
    </div>
  );
}

The generated hooks automatically handle cursor-based pagination if your API supports it. The nextCursor value is extracted from the response and used to fetch the next page.

Paginated APIs

If you have a paginated API which has its pagination parameter named something other than cursor, you can customise it using the x-cursor OpenAPI vendor extension.

Click here for an example using the client directly.

Error Handling

The integration includes built-in error handling with typed error responses. An <operation-name>Error type is generated which encapsulates the possible error responses defined in the OpenAPI specification. Each error has a status and error property, and by checking the value of status you can narrow to a specific type of error.

import { useMutation } from '@tanstack/react-query';

function MyComponent() {
  const api = useMyApi();
  const createItem = useMutation(api.createItem.mutationOptions());

  const handleClick = () => {
    createItem.mutate({ name: 'New Item' });
  };

  if (createItem.error) {
    switch (createItem.error.status) {
      case 400:
        // error.error is typed as CreateItem400Response
        return (
          <div>
            <h2>Invalid input:</h2>
            <p>{createItem.error.error.message}</p>
            <ul>
              {createItem.error.error.validationErrors.map((err) => (
                <li key={err.field}>{err.message}</li>
              ))}
            </ul>
          </div>
        );
      case 403:
        // error.error is typed as CreateItem403Response
        return (
          <div>
            <h2>Not authorized:</h2>
            <p>{createItem.error.error.reason}</p>
          </div>
        );
      case 500:
      case 502:
        // error.error is typed as CreateItem5XXResponse
        return (
          <div>
            <h2>Server error:</h2>
            <p>{createItem.error.error.message}</p>
            <p>Trace ID: {createItem.error.error.traceId}</p>
          </div>
        );
    }
  }

  return <button onClick={handleClick}>Create Item</button>;
}

Click here for an example using the vanilla client directly.

Consuming a Stream

If you have configured your FastAPI to stream responses, your useQuery hook will automatically update its data as new chunks of the stream arrive.

For example:

function MyStreamingComponent() {
  const api = useMyApi();
  const stream = useQuery(api.myStream.queryOptions());

  return (
    <ul>
      {(stream.data ?? []).map((chunk) => (
        <li>
          {chunk.timestamp.toISOString()}: {chunk.message}
        </li>
      ))}
    </ul>
  );
}

You can use the isLoading and fetchStatus properties to determine the current state of the stream if necessary. A stream follows this lifecycle:

1. The HTTP request to start streaming is sent

   • isLoading is true
   • fetchStatus is 'fetching'
   • data is undefined

2. The first chunk of the stream is received

   • isLoading becomes false
   • fetchStatus remains 'fetching'
   • data becomes an array containing the first chunk

3. Subsequent chunks are received

   • isLoading remains false
   • fetchStatus remains 'fetching'
   • data is updated with each subsequent chunk as soon as it is received

4. The stream completes

   • isLoading remains false
   • fetchStatus becomes 'idle'
   • data is an array of all received chunks

Click here for an example using the vanilla client directly.

Streaming APIs

If you have a streaming API which accepts a cursor parameter, when using the useInfiniteQuery hook, each page will wait for the stream to finish before it has been loaded.

Customising the Generated Code

Queries and Mutations

By default, operations in your FastAPI which use the HTTP methods PUT, POST, PATCH and DELETE are considered mutations, and all others are considered queries.

You can change this behaviour using x-query and x-mutation.

x-query

@app.post(
    "/items",
    openapi_extra={
        "x-query": True
    }
)
def list_items():
    # ...

The generated hook will provide queryOptions even though it uses the POST HTTP method:

const items = useQuery(api.listItems.queryOptions());

x-mutation

@app.get(
    "/start-processing",
    openapi_extra={
        "x-mutation": True
    }
)
def start_processing():
    # ...

The generated hook will provide mutationOptions even though it uses the GET HTTP method:

// Generated hook will include the custom options
const startProcessing = useMutation(api.startProcessing.mutationOptions());

Custom Pagination Cursor

By default, the generated hooks assume cursor-based pagination with a parameter named cursor. You can customize this behavior using the x-cursor extension:

@app.get(
    "/items",
    openapi_extra={
        # Specify a different parameter name for the cursor
        "x-cursor": "page_token"
    }
)
def list_items(page_token: str = None, limit: int = 10):
    # ...
    return {
        "items": items,
        "page_token": next_page_token
    }

If you would not like to generate infiniteQueryOptions for an operation, you can set x-cursor to False:

@app.get(
    "/items",
    openapi_extra={
        # Disable cursor-based pagination for this endpoint
        "x-cursor": False
    }
)
def list_items(page: int = 1, limit: int = 10):
    # ...
    return {
        "items": items,
        "total": total_count,
        "page": page,
        "pages": total_pages
    }

Grouping Operations

The generated hooks and client methods are automatically organized based on the OpenAPI tags in your FastAPI endpoints. This helps keep your API calls organized and makes it easier to find related operations.

For example:

items.py

@app.get(
    "/items",
    tags=["items"],
)
def list():
    # ...

@app.post(
    "/items",
    tags=["items"],
)
def create(item: Item):
    # ...

users.py

@app.get(
    "/users",
    tags=["users"],
)
def list():
    # ...

The generated hooks will be grouped by these tags:

import { useQuery, useMutation } from '@tanstack/react-query';
import { useMyApi } from './hooks/useMyApi';

function ItemsAndUsers() {
  const api = useMyApi();

  // Items operations are grouped under api.items
  const items = useQuery(api.items.list.queryOptions());
  const createItem = useMutation(api.items.create.mutationOptions());

  // Users operations are grouped under api.users
  const users = useQuery(api.users.list.queryOptions());

  // Usage example
  const handleCreateItem = () => {
    createItem.mutate({ name: 'New Item' });
  };

  return (
    <div>
      <h2>Items</h2>
      <ul>
        {items.data?.map(item => (
          <li key={item.id}>{item.name}</li>
        ))}
      </ul>
      <button onClick={handleCreateItem}>Add Item</button>

      <h2>Users</h2>
      <ul>
        {users.data?.map(user => (
          <li key={user.id}>{user.name}</li>
        ))}
      </ul>
    </div>
  );
}

This grouping makes it easier to organize your API calls and provides better code completion in your IDE.

Click here for an example using the client directly.

Splitting Your API

You can also split your API using multiple routers. See the FastAPI Documentation for more details.

Errors

You can customize error responses in your FastAPI by defining custom exception classes, exception handlers, and specifying response models for different error status codes. The generated client will automatically handle these custom error types.

Defining Custom Error Models

First, define your error models using Pydantic:

models.py

from pydantic import BaseModel

class ErrorDetails(BaseModel):
    message: str

class ValidationError(BaseModel):
    message: str
    field_errors: list[str]

Creating Custom Exceptions

Then create custom exception classes for different error scenarios:

exceptions.py

class NotFoundException(Exception):
    def __init__(self, message: str):
        self.message = message

class ValidationException(Exception):
    def __init__(self, details: ValidationError):
        self.details = details

Adding Exception Handlers

Register exception handlers to convert your exceptions to HTTP responses:

main.py

from fastapi import Request
from fastapi.responses import JSONResponse

@app.exception_handler(NotFoundException)
async def not_found_handler(request: Request, exc: NotFoundException):
    return JSONResponse(
        status_code=404,
        content=exc.message,
    )

@app.exception_handler(ValidationException)
async def validation_error_handler(request: Request, exc: ValidationException):
    return JSONResponse(
        status_code=400,
        content=exc.details.model_dump(),
    )

Custom Response Types

The JSONResponse accepts a dictionary, so we use our Pydantic model’s model_dump method.

Specifying Response Models

Finally, specify the response models for different error status codes in your endpoint definitions:

main.py

@app.get(
    "/items/{item_id}",
    responses={
        404: {"model": str}
        500: {"model": ErrorDetails}
    }
)
def get_item(item_id: str) -> Item:
    item = find_item(item_id)
    if not item:
        raise NotFoundException(message=f"Item with ID {item_id} not found")
    return item

@app.post(
    "/items",
    responses={
        400: {"model": ValidationError},
        403: {"model": str}
    }
)
def create_item(item: Item) -> Item:
    if not is_valid(item):
        raise ValidationException(
            ValidationError(
                message="Invalid item data",
                field_errors=["name is required"]
            )
        )
    return save_item(item)

Using Custom Error Types in React

The generated client will automatically handle these custom error types, allowing you to type-check and handle different error responses:

import { useMutation, useQuery } from '@tanstack/react-query';

function ItemComponent() {
  const api = useMyApi();

  // Query with typed error handling
  const getItem = useQuery({
    ...api.getItem.queryOptions({ itemId: '123' }),
    onError: (error) => {
      // Error is typed based on the responses in your FastAPI
      switch (error.status) {
        case 404:
          // error.error is a string as specified in the responses
          console.error('Not found:', error.error);
          break;
        case 500:
          // error.error is typed as ErrorDetails
          console.error('Server error:', error.error.message);
          break;
      }
    }
  });

  // Mutation with typed error handling
  const createItem = useMutation({
    ...api.createItem.mutationOptions(),
    onError: (error) => {
      switch (error.status) {
        case 400:
          // error.error is typed as ValidationError
          console.error('Validation error:', error.error.message);
          console.error('Field errors:', error.error.field_errors);
          break;
        case 403:
          // error.error is a string as specified in the responses
          console.error('Forbidden:', error.error);
          break;
      }
    }
  });

  // Component rendering with error handling
  if (getItem.isError) {
    if (getItem.error.status === 404) {
      return <NotFoundMessage message={getItem.error.error} />;
    } else {
      return <ErrorMessage message={getItem.error.error.message} />;
    }
  }

  return (
    <div>
      {/* Component content */}
    </div>
  );
}

Click here for an example using the client directly.

Error Responses

When defining error responses in FastAPI, always use the responses parameter to specify the model for each status code. This ensures that the generated client will have proper type information for error handling.

Best Practices

Handle Loading States

Always handle loading and error states for a better user experience:

import { useQuery } from '@tanstack/react-query';

function ItemList() {
  const api = useMyApi();
  const items = useQuery(api.listItems.queryOptions());

  if (items.isLoading) {
    return <LoadingSpinner />;
  }

  if (items.isError) {
    const err = items.error;
    switch (err.status) {
      case 403:
        // err.error is typed as ListItems403Response
        return <ErrorMessage message={err.error.reason} />;
      case 500:
      case 502:
        // err.error is typed as ListItems5XXResponse
        return (
          <ErrorMessage
            message={err.error.message}
            details={`Trace ID: ${err.error.traceId}`}
          />
        );
      default:
        return <ErrorMessage message="An unknown error occurred" />;
    }
  }

  return (
    <ul>
      {items.data.map((item) => (
        <li key={item.id}>{item.name}</li>
      ))}
    </ul>
  );
}

Click here for an example using the vanilla client directly.

Optimistic Updates

Implement optimistic updates for a better user experience:

import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';

function ItemList() {
  const api = useMyApi();
  const queryClient = useQueryClient();

  // Query to fetch items
  const itemsQuery = useQuery(api.listItems.queryOptions());

  // Mutation for deleting items with optimistic updates
  const deleteMutation = useMutation({
    ...api.deleteItem.mutationOptions(),
    onMutate: async (itemId) => {
      // Cancel any outgoing refetches
      await queryClient.cancelQueries({ queryKey: api.listItems.queryKey() });

      // Snapshot the previous value
      const previousItems = queryClient.getQueryData(api.listItems.queryKey());

      // Optimistically update to the new value
      queryClient.setQueryData(
        api.listItems.queryKey(),
        (old) => old.filter((item) => item.id !== itemId)
      );

      // Return a context object with the snapshot
      return { previousItems };
    },
    onError: (err, itemId, context) => {
      // If the mutation fails, use the context returned from onMutate to roll back
      queryClient.setQueryData(api.listItems.queryKey(), context.previousItems);
      console.error('Failed to delete item:', err);
    },
    onSettled: () => {
      // Always refetch after error or success to ensure data is in sync with server
      queryClient.invalidateQueries({ queryKey: api.listItems.queryKey() });
    },
  });

  if (itemsQuery.isLoading) {
    return <LoadingSpinner />;
  }

  if (itemsQuery.isError) {
    return <ErrorMessage message="Failed to load items" />;
  }

  return (
    <ul>
      {itemsQuery.data.map((item) => (
        <li key={item.id}>
          {item.name}
          <button
            onClick={() => deleteMutation.mutate(item.id)}
            disabled={deleteMutation.isPending}
          >
            {deleteMutation.isPending ? 'Deleting...' : 'Delete'}
          </button>
        </li>
      ))}
    </ul>
  );
}

Click here for an example using the vanilla client directly.

Type Safety

The integration provides complete end-to-end type safety. Your IDE will provide full autocompletion and type checking for all your API calls:

import { useMutation } from '@tanstack/react-query';

function ItemForm() {
  const api = useMyApi();

  // Type-safe mutation for creating items
  const createItem = useMutation({
    ...api.createItem.mutationOptions(),
    // ✅ Type error if onSuccess callback doesn't handle the correct response type
    onSuccess: (data) => {
      // data is fully typed based on your API's response schema
      console.log(`Item created with ID: ${data.id}`);
    },
  });

  const handleSubmit = (data: CreateItemInput) => {
    // ✅ Type error if input doesn't match schema
    createItem.mutate(data);
  };

  // Error UI can use type narrowing to handle different error types
  if (createItem.error) {
    const error = createItem.error;
    switch (error.status) {
      case 400:
        // error.error is typed as CreateItem400Response
        return (
          <FormError
            message="Invalid input"
            errors={error.error.validationErrors}
          />
        );
      case 403:
        // error.error is typed as CreateItem403Response
        return <AuthError reason={error.error.reason} />;
      default:
        // error.error is typed as CreateItem5XXResponse for 500, 502, etc.
        return <ServerError message={error.error.message} />;
    }
  }

  return (
    <form onSubmit={(e) => {
      e.preventDefault();
      handleSubmit({ name: 'New Item' });
    }}>
      {/* Form fields */}
      <button
        type="submit"
        disabled={createItem.isPending}
      >
        {createItem.isPending ? 'Creating...' : 'Create Item'}
      </button>
    </form>
  );
}

Click here for an example using the vanilla client directly.

The types are automatically generated from your FastAPI’s OpenAPI schema, ensuring that any changes to your API are reflected in your frontend code after a build.

Custom Auth

If your FastAPI uses Custom authentication (Lambda Authorizer), you will need to edit the generated client provider to add the authorization headers your authorizer expects. Look for the fetch configuration in the generated <ApiName>Provider.tsx and add your token or API key to the request headers.