Скачать или смотреть How to Fix NestJS GraphQL Apollo Federation ResolveField Issues for Many-to-Many Relations

Discover how to troubleshoot and implement ResolveField for many-to-many relationships in NestJS with Apollo Federation to ensure proper data retrieval.
---
This video is based on the question https://stackoverflow.com/q/73948235/ asked by the user 'Alex Smirnoff' ( https://stackoverflow.com/u/848784/ ) and on the answer https://stackoverflow.com/a/73950830/ provided by the user 'Alex Smirnoff' ( https://stackoverflow.com/u/848784/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: NestJS GraphQL Apollo Federation many-to-many ResolveField is not triggered

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Fix NestJS GraphQL Apollo Federation ResolveField Issues for Many-to-Many Relations

If you're working with NestJS, GraphQL, and Apollo Federation, you might encounter a common challenge: properly implementing @ ResolveField() for many-to-many relationships. This post aims to guide you through troubleshooting and resolving the issue, particularly with a scenario involving three distinct services: User, Channel, and UserChannelMembership.

Understanding the Problem

In a federated architecture, each service holds its own GraphQL schema, yet they can relate to one another through defined relationships. In our case:

User and Channel services do not directly reference each other.

UserChannelMembership service serves as the intermediary that connects these two services through many-to-many relationships.

You have defined your schema and everything seems correct at first glance, yet when trying to retrieve data through the extended fields channelsPerUser and usersPerChannel, they return null. The primary concern is that @ ResolveField() functions are not being triggered as expected.

The Root of the Issue

The core issue arises from how Resolvers are registered and how GraphQL queries are executed in a federated context. Below are the essential points to consider:

Graphs with Federation: Each service operates its own GraphQL API & is combined at runtime; ensure resolvers are properly organized within each subgraph.

Service Registration: If the resolver classes are not registered correctly within their respective modules, the framework may not know how to handle the ResolveField directives.

Solution Steps

Here's a detailed breakdown of how to implement your @ ResolveField() properly:

Step 1: Create Separate Resolvers

It's crucial to separate the responsibilities of your resolvers as follows:

UserResolver: Handles the channelsPerUser field.

[[See Video to Reveal this Text or Code Snippet]]

ChannelResolver: Handles the usersPerChannel field.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Import Resolvers into the Module

Once you've created these resolvers, ensure that they are imported as providers in your module file. For instance:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Testing Your Implementation

After implementing your resolvers and correctly linking them within your module, perform a test query to see if the fields channelsPerUser and usersPerChannel return the expected data instead of null.

Final Thoughts

Implementing @ ResolveField() in a federated service architecture can be tricky, especially when dealing with many-to-many relationships. By separating your resolvers and ensuring they are properly registered as providers, you can overcome this hurdle.

Through the above steps, you should be able to successfully extend the User and Channel GraphQL types and fetch the necessary data.

Remember, patience and systematic debugging are key in such implementations. We hope this guide helps you navigate your issues with NestJS and Apollo Federation.