How to Properly Omit Zero-Value Time Fields in JSON Marshaling?

Customizing JSON Marshaling for Time Fields with Omission Tag

One of the challenges when utilizing JSON with time fields is ensuring that they are omitted when not set. Despite using the json:",omitempty" tag, the desired outcome of excluding time.Time fields with a zero value may not occur.

To understand this behavior, it is crucial to recognize that the "zero" value for structs differs from that of other data types. For structs, a zero value represents a valid structural instance where all fields contain their respective zero values, making it distinct from empty values.

A solution to this challenge lies in converting time.Time fields into pointers. Nil pointers are inherently treated as "empty" during JSON marshaling and unmarshaling, circumventing the issue of omitting zero-valued time fields.

type MyStruct struct {
    Timestamp *time.Time `json:",omitempty"`
    Date      *time.Time `json:",omitempty"`
    Field     string     `json:",omitempty"`
}

By using pointers for time fields, we can effectively achieve the desired outcome:

ts := time.Date(2015, 9, 18, 0, 0, 0, 0, time.UTC)
ms := MyStruct{
    Timestamp: &ts,
    Field:     "",
}

This solution produces the desired JSON output:

{"Timestamp":"2015-09-18T00:00:00Z"}

Alternatively, if modifying the struct to utilize pointers is undesirable, implementing custom Marshaler and Unmarshaler interfaces provides an avenue for tailoring the behavior of JSON marshaling and unmarshaling for time.Time fields. Utilizing the Time.IsZero() method allows for precise control over whether to exclude time.Time fields based on their zero value.

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