v4 code migration guide

Strapi v4 introduces breaking changes that require manually updating the codebase of an existing Strapi project.

This guide covers migrating both the backend and the frontend of a Strapi v3.6.x application to Strapi v4.0.x. and is built around small independent topics.

Migrating the backend code of a Strapi application is a prerequisite to migrating the frontend.

For each topic covered, this guide is designed to:

help you understand the main differences between Strapi v3 and v4,
help you resolve breaking changes by migrating built-in code to Strapi v4,
and, whenever possible, offer some clues and starting points on how to migrate custom code.

The following topics are covered by this guide, and you can either click on a specific topic to jump to the dedicated migration documentation or click on a scope to read a more general introduction for the backend or the frontend migration:

Scope	Topic
Backend code migration	Configuration Dependencies Routes Controllers Services Content-type schema Policies Route middlewares Global middlewares GraphQL resolvers
Frontend code migration	WYSIWYG customizations Translations Webpack configuration Theme customizations Calls to the `strapi` global variable

note

The following topics are not extensively covered in this code migration guide, but Strapi v4 also introduces:

a new file structure for the project, which can be migrated with the help of Strapi codemods,
fully rewritten REST and GraphQL APIs, with the REST API not populating by default any relations, components, dynamic zones, and medias,
the new Entity Service and Query Engine APIs,
and the Strapi Design System which is used to build the new user interface of Strapi v4.

:::strapi Need more help? Feel free to ask for help on the forum or on the community Discord. :::