


How Can I Differentiate Between Empty and Missing Fields When Unmarshalling JSON in Go?
Dec 14, 2024 pm 07:55 PMDistinguishing Void Values from Unspecified Fields in Go Unmarshaling
Unmarshalling JSON data in Golang can be straightforward, but differentiating between void values and unspecified field values can be a challenge. This article addresses this issue, providing a solution to distinguish between the two.
In the provided example, we have a slice of Category structs, where each category has a Name and Description field. When unmarshaling JSON data into this slice, we encounter a scenario where both category B and category C have empty Description fields. However, we want to know if there's a way to discern whether category B's Description is specified as an empty string or simply not present in the JSON data.
The key is to declare the Description field as a pointer to a string:
type Category struct { Name string Description *string }
By using a pointer, if a JSON field is present with an empty string value, it will be set to a pointer pointing to an empty string (*""). Conversely, if the field is not present in JSON, the pointer will be left nil (
The updated output exemplifies this differentiation:
[{Name:A Description:0x1050c150} {Name:B Description:<nil>} {Name:C Description:0x1050c158}]
Here, category A's Description is non-empty, category B's Description is nil (indicating an unspecified field), and category C's Description is an empty string (indicating a specified empty value).
This technique allows you to distinguish between void values (nil) and unspecified fields (nil pointers), enabling you to tailor your program's behavior accordingly.
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