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# JSON Merge Patch

The library supports JSON Merge Patch (RFC 7386) as a patch format. 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.

Instead of using JSON Pointer to specify values to be manipulated, it describes the changes using a syntax that closely mimics the document being modified.

Example

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

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

    using json = nlohmann::json;

    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!"
    }