How to Create a Resolver for Updating Items in DynamoDB via AppSync Using AWS CDK

Discover how to implement a clear and effective resolver for updating items in DynamoDB through AppSync with AWS CDK. This guide breaks down the process into manageable steps.
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How to Create a Resolver for Updating Items in DynamoDB via AppSync Using AWS CDK

Creating a robust API using AWS can seem daunting, especially when it comes to efficiently managing database operations. One common task many developers face is creating a resolver that allows for updating items in a DynamoDB table through AWS AppSync. If you've successfully set up a resolver to create items but are now unsure how to update them, this guide is here to help!

Understanding the Challenge

When working with AWS AppSync and DynamoDB, you may find yourself needing to create resolvers for various operations on your data. While you may have already accomplished this for creating items, updating items can seem a bit tricky at first. The good news is that the process is quite similar!

What is a Resolver?

In AWS AppSync, a resolver is a set of instructions that tells the service how to interact with your data source when a specific query or mutation is made. For our use case, we will create a resolver specifically for updating an item in a DynamoDB table.

Solution: Creating an Update Resolver

The update resolver in DynamoDB works in a comparable way to the create resolver, as both operations utilize a PutItem request. Below we will walk through the steps needed to create an update resolver, including variations based on whether the ID is included in the input.

1. Update Resolver for Input with ID

If your input structure includes the ID of the item you wish to update, you will set up your resolver like this:

GraphQL Schema Example:

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Resolver Code:

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2. Update Resolver for Input without ID

If you prefer to pass the ID separately from the input object, follow this approach:

GraphQL Schema Example:

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Resolver Code:

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Real-world Example

Here’s how I implemented these concepts in my project involving labels:

GraphQL Schema

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Corresponding Resolvers Implementation

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Conclusion

Setting up resolvers in AppSync for updating DynamoDB items can seem challenging, but with a clear understanding of input structures and mapping templates, you can streamline your API development process. By following the patterns outlined in this guide, you can confidently create update resolvers tailored to your application's needs.

If you have any questions or need further assistance, feel free to reach out. Happy coding!