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nlohmann
124 lines
2.5 KiB
Markdown
124 lines
2.5 KiB
Markdown
# nlohmann::basic_json::diff
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```
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static basic_json diff(const basic_json& source,
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const basic_json& target);
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```
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Creates a [JSON Patch](http://jsonpatch.com) so that value `source` can be changed into the value `target` by calling [`patch`](https://json.nlohmann.me/api/basic_json/patch/index.md) function.
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For two JSON values `source` and `target`, the following code yields always `true`:
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```
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source.patch(diff(source, target)) == target;
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```
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## Parameters
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`source` (in) : JSON value to compare from
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`target` (in) : JSON value to compare against
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## Return value
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a JSON patch to convert the `source` to `target`
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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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## Complexity
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Linear in the lengths of `source` and `target`.
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## Notes
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Currently, only `remove`, `add`, and `replace` operations are generated.
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## Examples
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Example
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The following code shows how a JSON patch is created as a diff for two JSON values.
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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 source document
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json source = 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 target document
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json target = R"(
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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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)"_json;
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// create the patch
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json patch = json::diff(source, target);
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// roundtrip
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json patched_source = source.patch(patch);
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// output patch and roundtrip result
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std::cout << std::setw(4) << patch << "\n\n"
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<< std::setw(4) << patched_source << 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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{
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"op": "replace",
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"path": "/baz",
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"value": "boo"
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},
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{
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"op": "remove",
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"path": "/foo"
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},
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{
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"op": "add",
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"path": "/hello",
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"value": [
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"world"
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]
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}
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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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- [patch](https://json.nlohmann.me/api/basic_json/patch/index.md) applies a JSON Patch
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- [patch_inplace](https://json.nlohmann.me/api/basic_json/patch_inplace/index.md) applies a JSON Patch in place
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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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