How Can I Handle Inconsistent JSON Fields (Strings vs. Arrays) in Go?

Unmarshalling JSON with Inconsistent Fields: Handling Strings and Arrays

When unmarshalling JSON data into a Go struct, it can be challenging to handle fields that can vary in type. For example, a field might be a string in most cases but an array of strings on occasion. To tackle this issue, we present a solution that leverages Go's powerful JSON parsing capabilities.

Capturing the Varying Field with json.RawMessage

The key to handling inconsistent JSON fields lies in capturing the raw data using json.RawMessage. This type is a slice of bytes that stores the unparsed JSON value. By storing the raw data, we have the flexibility to parse it later depending on its specific type.

Hiding the DisplayName Field and Filling It Post-Decoding

To prevent the decoder from attempting to interpret the DisplayName field before we have the relevant data, we hide it using the JSON "-" name. This name instructs the decoder to ignore the field during the initial unmarshalling. After the top-level JSON has been decoded, we manually fill the DisplayName field based on the parsed raw data.

Handling the Various Types of Raw Data

Depending on whether the raw data is a string or an array of strings, we proceed as follows:

• If the raw data is a string, we unmarshal it into a single string and assign it to DisplayName.
• If the raw data is an array of strings, we unmarshal it into a slice of strings and store it in DisplayName after joining the strings with a delimiter.

Integrating into a Loop for MyListings

To handle a list of items, such as MyListings, we can iterate through each item and perform the same unmarshalling logic as described above. This allows us to handle any inconsistencies in the DisplayName field for each item.

Encapsulating the Logic with a Custom Unmarshaler

If multiple fields in the data model can have inconsistent types, it can be beneficial to encapsulate the logic in a custom type that implements the json.Unmarshaler interface. This simplifies the process and reduces duplication.

In conclusion, by employing json.RawMessage and hiding the varying field, we can effectively unmarshal JSON data with inconsistent fields, ensuring that all necessary data is captured and parsed correctly. The provided examples and playground links demonstrate the solution in practice.

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