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nlohmann
111 lines
2.6 KiB
Markdown
111 lines
2.6 KiB
Markdown
# nlohmann::basic_json::merge_patch
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```
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void merge_patch(const basic_json& apply_patch);
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```
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The merge patch format is primarily intended for use with the HTTP PATCH method as a means of describing a set of modifications to a target resource's content. This function applies a merge patch to the current JSON value.
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The function implements the following algorithm from Section 2 of [RFC 7396 (JSON Merge Patch)](https://tools.ietf.org/html/rfc7396):
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```
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define MergePatch(Target, Patch):
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if Patch is an Object:
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if Target is not an Object:
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Target = {} // Ignore the contents and set it to an empty Object
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for each Name/Value pair in Patch:
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if Value is null:
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if Name exists in Target:
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remove the Name/Value pair from Target
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else:
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Target[Name] = MergePatch(Target[Name], Value)
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return Target
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else:
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return Patch
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```
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Thereby, `Target` is the current object; that is, the patch is applied to the current value.
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## Parameters
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`apply_patch` (in) : the patch to apply
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## Complexity
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Linear in the lengths of `apply_patch`.
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## Examples
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Example
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The following code shows how a JSON Merge Patch is applied to a JSON document.
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```
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#include <iostream>
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#include <nlohmann/json.hpp>
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#include <iomanip> // for std::setw
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using json = nlohmann::json;
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using namespace nlohmann::literals;
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int main()
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{
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// the original document
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json document = R"({
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"title": "Goodbye!",
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"author": {
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"givenName": "John",
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"familyName": "Doe"
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},
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"tags": [
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"example",
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"sample"
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],
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"content": "This will be unchanged"
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})"_json;
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// the patch
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json patch = R"({
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"title": "Hello!",
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"phoneNumber": "+01-123-456-7890",
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"author": {
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"familyName": null
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},
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"tags": [
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"example"
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]
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})"_json;
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// apply the patch
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document.merge_patch(patch);
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// output original and patched document
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std::cout << std::setw(4) << document << std::endl;
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}
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```
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Output:
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```
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{
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"author": {
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"givenName": "John"
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},
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"content": "This will be unchanged",
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"phoneNumber": "+01-123-456-7890",
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"tags": [
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"example"
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],
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"title": "Hello!"
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}
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```
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## See also
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- [RFC 7396 (JSON Merge Patch)](https://tools.ietf.org/html/rfc7396)
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- [patch](https://json.nlohmann.me/api/basic_json/patch/index.md) apply a JSON patch
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## Version history
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- Added in version 3.0.0.
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