Run Tasks for Affected Projects

Nx doesn’t just cache your task results, it can also eliminate the need to run unnecessary tasks.

First, commit any outstanding changes to the main branch locally:

git commit -am "changes"

Next make a small change to the application code:

package com.example.multimodule.application;

import com.example.multimodule.service.MyService;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication(scanBasePackages = "com.example.multimodule")
@RestController
public class DemoApplication {

    private final MyService myService;

    public DemoApplication(MyService myService) {
        this.myService = myService;
    }

    @GetMapping("/")
    public String home() {
        return myService.message() + " changed!";
    }

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

As a developer, we know that this change only affects the application project, not the library project. We would run ./nx run application:test to verify our changes. In CI, teams often run all test tasks rerunning the library:test task unnecessarily.

For a repository with only a few projects, you can manually calculate which projects are affected. As the repository grows, it becomes critical to have a tool like Nx that understands the project dependency graph and eliminates wasted time in CI.

The ./nx affected command solves this problem. Nx uses its project graph in conjunction with git history to only run tasks for projects that may have been affected by the changes that you made.

To run the test tasks for projects affected by this change, run:

./nx affected -t test

Notice that this command does not run the test task for the library project, since it could not have been affected by the code change.