Fixing json: cannot unmarshal object into Go struct Error in Go

Описание: Learn how to resolve the `json: cannot unmarshal object into Go struct` error when parsing JSON in Go by using the correct data structures.
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This video is based on the question https://stackoverflow.com/q/66854658/ asked by the user 'Jocelyn' ( https://stackoverflow.com/u/13719504/ ) and on the answer https://stackoverflow.com/a/66854795/ provided by the user 'Burak Serdar' ( https://stackoverflow.com/u/11923999/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the json: cannot unmarshal object into Go struct Error in Go

Parsing JSON files in Go can sometimes lead to frustrating challenges, especially when the structure of the JSON data does not match your Go data types. One common error developers encounter is the message: json: cannot unmarshal object into Go value of type. If you are facing this problem, you're not alone! In this post, we'll break down how to resolve this issue step-by-step.

The Problem

You have a JSON file containing a list of contracts, where each contract has associated functions. The structure of this JSON file is as follows:

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

While trying to unmarshal this JSON into your Go application, you received the error:

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

This implies that the JSON structure does not align with the Go struct you have defined for ContractAll and its nested structures.

Understanding Your Go Structs

Here's a look at the Go struct definitions that led to the error:

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

Where It Went Wrong

ContractInfo is defined as a nested slice type (a slice of structs).

However, in your ContractAll struct, you are trying to declare it as a slice of ContractInfo, which is incorrect since contracts in the JSON is a list of objects, not a list of slices.

The Solution

To fix this problem, you need to adjust the definition of your structs. Specifically, you should create a new struct that matches the data structure of the JSON file. Here's how you can do it:

Step-by-Step Fix

Define a New Struct for the Contracts:

You need to create a new struct that represents the entire contracts field in your JSON data:

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

Update the Variable Declaration:

In your code, replace the variable contracts with the new struct type you just created:

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

Final Code Example

After the adjustments, your complete code should look like this:

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

Conclusion

The json: cannot unmarshal object into Go struct error often arises from mismatched struct definitions. By carefully aligning your Go structs with the structure of your JSON data, you can eliminate this type of error. Always ensure that your collections (slices and arrays) are properly defined according to what the JSON represents.

By following the steps in this post, you should now be able to successfully parse a JSON file with Go without running into the unmarshalling issue again. Happy coding!