merge_patch - JSON for Modern C++ (original) (raw)

nlohmann::basic_json::merge_patch¶

void merge_patch(const basic_json& apply_patch);

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.

The function implements the following algorithm from Section 2 of RFC 7396 (JSON Merge Patch):

define MergePatch(Target, Patch): if Patch is an Object: if Target is not an Object: Target = {} // Ignore the contents and set it to an empty Object for each Name/Value pair in Patch: if Value is null: if Name exists in Target: remove the Name/Value pair from Target else: Target[Name] = MergePatch(Target[Name], Value) return Target else: return Patch

Thereby, Target is the current object; that is, the patch is applied to the current value.

Parameters¶

apply_patch (in)

the patch to apply

Complexity¶

Linear in the lengths of apply_patch.

Examples¶

Example

The following code shows how a JSON Merge Patch is applied to a JSON document.

`#include #include <nlohmann/json.hpp> #include // for std::setw

using json = nlohmann::json; using namespace nlohmann::literals;

int main() { // the original document json document = R"({ "title": "Goodbye!", "author": { "givenName": "John", "familyName": "Doe" }, "tags": [ "example", "sample" ], "content": "This will be unchanged" })"_json;

// the patch
json patch = R"({
            "title": "Hello!",
            "phoneNumber": "+01-123-456-7890",
            "author": {
                "familyName": null
            },
            "tags": [
                "example"
            ]
        })"_json;

// apply the patch
document.merge_patch(patch);

// output original and patched document
std::cout << std::setw(4) << document << std::endl;

} `

Output:

{ "author": { "givenName": "John" }, "content": "This will be unchanged", "phoneNumber": "+01-123-456-7890", "tags": [ "example" ], "title": "Hello!" }

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