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

nlohmann::basic_json::patch¶

basic_json patch(const basic_json& json_patch) const;

JSON Patch defines a JSON document structure for expressing a sequence of operations to apply to a JSON document. With this function, a JSON Patch is applied to the current JSON value by executing all operations from the patch.

Parameters¶

json_patch (in)

JSON patch document

Return value¶

patched document

Exception safety¶

Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

Exceptions¶

• Throws parse_error.104 if the JSON patch does not consist of an array of objects.
• Throws parse_error.105 if the JSON patch is malformed (e.g., mandatory attributes are missing); example: "operation add must have member path".
• Throws out_of_range.401 if an array index is out of range.
• Throws out_of_range.403 if a JSON pointer inside the patch could not be resolved successfully in the current JSON value; example: "key baz not found".
• Throws out_of_range.405 if JSON pointer has no parent ("add", "remove", "move")
• Throws out_of_range.501 if "test" operation was unsuccessful.

Complexity¶

Linear in the size of the JSON value and the length of the JSON patch. As usually the patch affects only a fraction of the JSON value, the complexity can usually be neglected.

Notes¶

The application of a patch is atomic: Either all operations succeed and the patched document is returned or an exception is thrown. In any case, the original value is not changed: the patch is applied to a copy of the value.

Examples¶

Example

The following code shows how a JSON patch is applied to a value.

`#include #include #include <nlohmann/json.hpp>

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

int main() { // the original document json doc = R"( { "baz": "qux", "foo": "bar" } )"_json;

// the patch
json patch = R"(
    [
      { "op": "replace", "path": "/baz", "value": "boo" },
      { "op": "add", "path": "/hello", "value": ["world"] },
      { "op": "remove", "path": "/foo"}
    ]
)"_json;

// apply the patch
json patched_doc = doc.patch(patch);

// output original and patched document
std::cout << std::setw(4) << doc << "\n\n"
          << std::setw(4) << patched_doc << std::endl;

} `

Output:

`{ "baz": "qux", "foo": "bar" }

{ "baz": "boo", "hello": [ "world" ] } `

See also¶

• RFC 6902 (JSON Patch)
• RFC 6901 (JSON Pointer)
• patch_inplace applies a JSON Patch without creating a copy of the document
• merge_patch applies a JSON Merge Patch

Version history¶

• Added in version 2.0.0.