Composer manages dependencies in PHP projects by letting you declare required libraries with version constraints in composer.json, while composer.lock records exact installed versions. 1. composer.json defines project metadata and dependencies with version ranges (e.g., "monolog/monolog": "^2.0"). 2. composer.lock locks dependencies to exact versions (e.g., 2.9.1) after running composer install, ensuring consistency across environments. 3. Both files should be committed to version control to maintain predictable deployments and consistent dependency versions across local, staging, and production environments.

Composer manages dependencies in a PHP project by allowing you to declare the libraries your project depends on, and it automatically installs and updates them for you. It uses two main files — composer.json and composer.lock — to keep track of what needs to be installed and exactly which versions are used.

What is composer.json?

The composer.json file is where you define your project's metadata and its dependencies. This includes things like:

• The name of your project
• Required packages and their version constraints
• Autoloading settings
• Scripts you want to run at certain stages

For example, if your project needs the monolog/monolog package, you might have a line like this in your composer.json:

"require": {
    "monolog/monolog": "^2.0"
}

This tells Composer that your project requires version 2.x of Monolog, but not 3.0 or later. When someone runs composer install, Composer will try to find the best matching version based on these constraints.

You can create or update this file manually or use commands like composer require monolog/monolog which will automatically add the dependency with a suggested version.

What is composer.lock?

When you first run composer install, Composer resolves all dependencies and writes exact versions into the composer.lock file. This ensures that everyone working on the project (or deploying it) gets the same versions of every package.

For example, even though your composer.json says "monolog/monolog": "^2.0", the composer.lock might show that version 2.9.1 was installed. That way, when another developer runs composer install, they’ll get exactly 2.9.1, not a newer patch or minor version.

If you later run composer update, Composer will look for the latest versions that match your constraints in composer.json, and update both the installed packages and the composer.lock file accordingly.

So:

• composer.json defines what you need (with version ranges)
• composer.lock records exactly what was installed

This helps avoid surprises from automatic upgrades and keeps environments consistent.

When should I commit these files?

You should always commit both composer.json and composer.lock to version control.

• Committing composer.json makes sense because it’s how anyone knows what your project needs.
• Committing composer.lock ensures that every environment (local, staging, production) uses the exact same versions — which helps prevent bugs caused by subtle differences between versions.

Only skip committing composer.lock if you're building a library that needs to test against multiple versions of dependencies, and even then, it's usually better to rely on CI tools or specific testing strategies rather than skipping the lock file.

That’s how Composer handles dependencies using composer.json and composer.lock. It gives you flexibility during development while keeping deployments predictable.

The above is the detailed content of How does Composer manage dependencies in a PHP project, and what is the role of composer.json and composer.lock?. For more information, please follow other related articles on the PHP Chinese website!