Скачать или смотреть How to Perform a GraphQL Lazy Query with Apollo Client After an Initial Query Success

Learn how to use Apollo Client's useLazyQuery hook correctly to make further queries after an initial GraphQL query succeeds, avoiding common pitfalls like variable redeclaration errors.
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This video is based on the question https://stackoverflow.com/q/72020339/ asked by the user 'Nelson Michael' ( https://stackoverflow.com/u/15068287/ ) and on the answer https://stackoverflow.com/a/72020385/ provided by the user 'KnowYourElements' ( https://stackoverflow.com/u/14389341/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Lazy Queries with Apollo Client

If you're delving into the world of GraphQL with Apollo Client, you might be trying to make efficient data retrievals using lazy queries. A common scenario is wanting to perform subsequent queries only after a successful initial query. However, this can lead to some tricky situations in your code, particularly with variable redeclarations.

This guide will walk you through the issues you might face when using Apollo Client's useLazyQuery hook multiple times, especially regarding variable scopes.

The Problem: Redeclaration Errors

When working with GraphQL queries using Apollo, you may want to make several queries that depend on each other. However, you might run into an error message like:

"Cannot redeclare block-scoped variable"

This error typically occurs when you try to declare the same variable name in the same scope. Let’s break down a common scenario that could lead to this issue.

Example Scenario

Imagine you want to:

Query user data based on a username.

After successfully retrieving that user data, make another query for their relationships.

A naive implementation might look like this:

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

What's Wrong Here?

In the above code, you’re trying to unpack data, loading, and error from two different useLazyQuery hooks. Since you’re using the same variable names, JavaScript throws a redeclaration error because both data variables exist in the same scope.

The Solution: Unique Variable Names

To resolve this issue, you need to use unique names for each query's returned variables. Here's how to do it:

Correcting Your Code

Instead of using the same variable names, change your code to assign unique names for each query's result:

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

Key Points to Note

Destructure Variables with Unique Names: By naming them differently, you can avoid conflicts when calling multiple queries.

Example Console Logging: You can comfortably log your queries without worrying about scope issues.

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

Conclusion

Using the Apollo Client's useLazyQuery can greatly enhance your application's data handling capabilities, but it requires careful attention to variable naming. By ensuring your variables are uniquely named for each query, you can avoid common errors and maintain clear, functional code.

Remember, when engaging with complex queries, keeping track of your variable names is crucial. Happy coding!