JSON Patch and Diff¶

Patches¶

JSON Patch (RFC 6902) defines a JSON document structure for expressing a sequence of operations to apply to a JSON document. With the patch function, a JSON Patch is applied to the current JSON value by executing all operations from the patch.

Example

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

#include<iostream>
#include<iomanip>
#include<nlohmann/json.hpp>
usingjson=nlohmann::json;
usingnamespacenlohmann::literals;
intmain()
{
// the original document
jsondoc=R"(
 {
 "baz": "qux",
 "foo": "bar"
 }
)"_json;
// the patch
jsonpatch=R"(
 [
 { "op": "replace", "path": "/baz", "value": "boo" },
 { "op": "add", "path": "/hello", "value": ["world"] },
 { "op": "remove", "path": "/foo"}
 ]
)"_json;
// apply the patch
jsonpatched_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"
]
}

Diff¶

The library can also calculate a JSON patch (i.e., a diff) given two JSON values.

Invariant

For two JSON values source and target, the following code yields always true:

source.patch(diff(source, target)) == target;

Example

The following code shows how a JSON patch is created as a diff for two JSON values.

#include<iostream>
#include<iomanip>
#include<nlohmann/json.hpp>
usingjson=nlohmann::json;
usingnamespacenlohmann::literals;
intmain()
{
// the source document
jsonsource=R"(
 {
 "baz": "qux",
 "foo": "bar"
 }
)"_json;
// the target document
jsontarget=R"(
 {
 "baz": "boo",
 "hello": [
 "world"
 ]
 }
)"_json;
// create the patch
jsonpatch=json::diff(source,target);
// roundtrip
jsonpatched_source=source.patch(patch);
// output patch and roundtrip result
std::cout<<std::setw(4)<<patch<<"\n\n"
<<std::setw(4)<<patched_source<<std::endl;
}

Output:

[
{
"op":"replace",
"path":"/baz",
"value":"boo"
},
{
"op":"remove",
"path":"/foo"
},
{
"op":"add",
"path":"/hello",
"value":[
"world"
]
}
]
{
"baz":"boo",
"hello":[
"world"
]
}