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nlohmann
108 lines
3.8 KiB
Markdown
108 lines
3.8 KiB
Markdown
# nlohmann::basic_json::patch
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```
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basic_json patch(const basic_json& json_patch) const;
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```
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[JSON Patch](http://jsonpatch.com) 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.
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## Parameters
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`json_patch` (in) : JSON patch document
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## Return value
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patched document
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## Exception safety
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Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
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## Exceptions
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- Throws [`parse_error.104`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error104) if the JSON patch does not consist of an array of objects.
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- Throws [`parse_error.105`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error105) if the JSON patch is malformed (e.g., mandatory attributes are missing); example: `"operation add must have member path"`.
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- Throws [`out_of_range.401`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range401) if an array index is out of range.
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- Throws [`out_of_range.403`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range403) if a JSON pointer inside the patch could not be resolved successfully in the current JSON value; example: `"key baz not found"`.
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- Throws [`out_of_range.405`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range405) if JSON pointer has no parent ("add", "remove", "move")
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- Throws [`out_of_range.411`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range411) if an "add" operation's target location has a parent that is neither an object nor an array.
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- Throws [`other_error.501`](https://json.nlohmann.me/home/exceptions/#jsonexceptionother_error501) if "test" operation was unsuccessful.
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## Complexity
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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.
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## Notes
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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.
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## Examples
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Example
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The following code shows how a JSON patch is applied to a value.
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```
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#include <iostream>
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#include <iomanip>
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#include <nlohmann/json.hpp>
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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 doc = R"(
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{
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"baz": "qux",
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"foo": "bar"
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}
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)"_json;
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// the patch
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json patch = R"(
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[
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{ "op": "replace", "path": "/baz", "value": "boo" },
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{ "op": "add", "path": "/hello", "value": ["world"] },
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{ "op": "remove", "path": "/foo"}
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]
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)"_json;
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// apply the patch
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json patched_doc = doc.patch(patch);
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// output original and patched document
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std::cout << std::setw(4) << doc << "\n\n"
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<< std::setw(4) << patched_doc << 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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"baz": "qux",
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"foo": "bar"
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}
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{
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"baz": "boo",
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"hello": [
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"world"
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]
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}
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```
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## See also
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- [RFC 6902 (JSON Patch)](https://tools.ietf.org/html/rfc6902)
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- [RFC 6901 (JSON Pointer)](https://tools.ietf.org/html/rfc6901)
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- [patch_inplace](https://json.nlohmann.me/api/basic_json/patch_inplace/index.md) applies a JSON Patch without creating a copy of the document
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- [merge_patch](https://json.nlohmann.me/api/basic_json/merge_patch/index.md) applies a JSON Merge Patch
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## Version history
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- Added in version 2.0.0.
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- Added [`out_of_range.411`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range411) and stopped relying on an internal assertion when an "add" operation's target location has a non-object/non-array parent in version 3.12.x.
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