How to Unmarshal Nested JSON with Unknown Structure?

Unmarshaling Nested JSON with Unknown Structure

When working with a database that stores JSON documents with varying structures, it can be challenging to unmarshal the data into specific structs without knowing the exact structure beforehand. Here we explore two approaches to address this issue.

Checking the Type

Before unmarshaling the JSON data, we need to determine its type. This can be achieved using one of the following methods:

• Unmarshal into a map[string]interface{}: By unmarshaling the json.RawMessage into a map, we can access the "type" field to identify the type of the data. This approach allows us to avoid repeated unmarshals.
• Use a regular expression to extract the type string: We can use a regular expression to search for the "type" field and extract its value, which can then be compared against known types.

Unmarshaling into a Specific Struct

Once we have determined the type of the JSON data, we can unmarshal it into the corresponding struct. In your case, if you know the possible types beforehand, you can create a series of if-else statements or a switch statement to unmarshal the data into the appropriate struct.

Avoiding Repeated Unmarshals

To avoid repeated unmarshals, you can create a copy of the json.RawMessage and Unmarshal it into the interface first. Once you know the type, you can Unmarshal the original json.RawMessage into the struct of the determined type.

Using a Regular Expression to Determine Type

If you prefer using a regular expression, you can follow the steps below:

1. Use the regexp.MustCompile function to create a regular expression that matches the "type" field.
2. Use the regexp.FindStringSubmatch function to extract the type string.
3. Use the extracted type string to determine the appropriate struct for unmarshalling.

Conclusion

By using the above approaches, you can efficiently unmarshal nested JSON data without knowing its exact structure. This allows for greater flexibility and convenience when working with dynamic data sources.

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