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Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Use a pointer field in a Go request DTO when an update needs to distinguish a supplied zero value—such as false, 0, or ""—from a field the client did not supply. But a pointer alone does not reliably preserve three distinct JSON states: omitted, explicit null, and concrete value. If those states mean different things to your API, track member presence separately or choose a patch format that expresses the intended operation.
Decide what omission and null mean first
Consider a partial update to display_name. The request can omit the member, send it as null, or send a value. Those are different inputs, and your API must define their effects before you choose a Go type.
| JSON request | Common intended meaning | Information the server needs |
|---|---|---|
| Member absent | Leave the stored value unchanged | Whether the member was present |
"display_name": null |
Clear the value or reject the request | Presence and whether the value was null |
"display_name": "" or another concrete value |
Set the value, including an empty string | Presence and the supplied value |
The same issue applies to false and 0: they can be valid requested updates, not signs that a field was omitted. Keep the patch request DTO distinct from a persistence or domain struct when reusing that struct would collapse meaningful input states.
When pointer fields are the right fit
A request field such as Name *string is compact and idiomatic when the API needs to distinguish “no concrete value” from a supplied string, and does not assign separate update meanings to omission and explicit JSON null. A non-nil pointer can retain concrete values such as an empty string; a nil pointer does not provide a durable distinction between absent and null.
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That makes pointers useful for optional fields where omission means “leave unchanged” and null is either treated the same way or is not a meaningful independent instruction. If null must clear a value while omission leaves it alone, a pointer field by itself is not enough.
When to track presence and null separately
Optionality and nullability are separate questions. A nullable value can represent null, but without input-presence tracking it may not say whether the client omitted the member or explicitly sent null.
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When all three states matter, use a presence-aware representation: for example, a wrapper conceptually holding Set, Null, and Value, or inspect raw JSON members before converting them into application values. The decoder must mark a member as set when it appears, including when its value is null.
This is a design pattern, not drop-in implementation code. Define and verify behavior for omitted fields, nulls, malformed values, repeated decoding into a reused object, nested structures, validation, and output marshaling in the JSON package and Go version your application uses.
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What omitempty does—and does not do
In Go’s encoding/json, omitempty describes encoding behavior: it omits empty values such as false, 0, nil pointers or interfaces, and empty arrays, slices, maps, and strings. The omitzero option omits a Go zero value and supports an IsZero method. Neither option records whether an incoming JSON member was present.
The versioned Go v1 package documentation and Go v2 package documentation describe these as marshaling options; v2 explicitly states that omitempty has no effect when unmarshaling. Check the documentation for the package and Go version your project uses rather than assuming an output tag solves input presence tracking.
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Choose a patch format when the wire contract calls for one
A DTO representation and a patch protocol solve related but different problems. Use the protocol whose semantics match the API’s update contract, especially for nested objects, arrays, and null values.
JSON Merge Patch
RFC 7396 defines JSON Merge Patch with the media type application/merge-patch+json. An omitted object member leaves the target member untouched; a member set to null removes it. That is a natural fit when null means removal, but not when an explicit null must be represented as an ordinary stored value. The RFC’s authors state: “This design means that merge patch documents are suitable for describing modifications to JSON documents that primarily use objects for their structure and do not make use of explicit null values.”
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JSON Patch
RFC 6902 defines JSON Patch as a sequence of operation objects, with operations including add, remove, replace, move, copy, and test. Its media type is application/json-patch+json. An operation list is useful when clients need to express explicit actions, but the server must parse, validate, and apply those operations. RFC 6902 specifies that a failed operation means the patch document is not deemed successful, consistent with HTTP PATCH atomicity.
Compare the choices against your API
| Choice | Omitted versus null | Zero and empty values | Update model | Implementation considerations |
|---|---|---|---|---|
| Pointer field in a request DTO | Does not reliably distinguish absent from explicit null | Can retain supplied concrete values, including zero values, through a non-nil pointer | Resource-shaped request fields | Good fit when null has no separate meaning; keep the DTO from blurring domain or persistence state |
| Presence-aware wrapper or raw-member tracking | Can represent absent, null, and value separately | Can retain supplied zero and empty values | Resource-shaped request fields with explicit presence semantics | Define decoding, validation, reuse, nesting, and marshaling behavior |
| JSON Merge Patch | Omission leaves the target member unchanged; null removes it | Concrete JSON values can be supplied | Object merge | Unsuitable when explicit null must be stored as an ordinary value |
| JSON Patch | Operations express actions rather than relying on member omission alone | Operation values carry the requested value | Explicit operation list | Server must validate and apply operations; a failed operation prevents success for the patch document |
Set the contract before implementing the DTO
Write down what clients may send and what each state does, then make decoding, validation, and persistence preserve those semantics.
- Specify whether omission means “leave unchanged.”
- Specify whether explicit
nullmeans clear, reject, or set a stored null. - Decide whether
false,0, and empty strings are valid updates. - Define behavior for invalid types, unknown fields, nested objects, arrays, and nullable values.
- Choose whether the endpoint accepts a resource-shaped DTO, Merge Patch, or JSON Patch, and document its media type and semantics.
- Ensure validation and persistence do not collapse distinctions the request contract promises to preserve.
Changing patch semantics later can break clients, so treat the patch format and its state meanings as part of the API contract.
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