diff()

template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer, class BinaryType = std::vector<std::uint8_t>>

static JSON_HEDLEY_WARN_UNUSED_RESULT basic_json nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::diff ( const basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType > &  source, const basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType > &  target, const std::string &  path = ""  )

inlinestatic

creates a diff as a JSON patch

Creates a JSON Patch so that value source can be changed into the value target by calling patch function.

Invariant

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

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

Note

Currently, only remove, add, and replace operations are generated.

Parameters

[in]	source	JSON value to compare from
[in]	target	JSON value to compare against
[in]	path	helper value to create JSON pointers

Returns

a JSON patch to convert the source to target

@complexity Linear in the lengths of source and target.

@liveexample{The following code shows how a JSON patch is created as a diff for two JSON values.,diff}

See also

see patch – apply a JSON patch

see merge_patch – apply a JSON Merge Patch

RFC 6902 (JSON Patch)

Since

version 2.0.0

Definition at line 26466 of file json.hpp.

    {
        // the patch
        basic_json result(value_t::array);
 
        // if the values are the same, return empty patch
        if (source == target)
        {
            return result;
        }
 
        if (source.type() != target.type())
        {
            // different types: replace value
            result.push_back(
            {
                {"op", "replace"}, {"path", path}, {"value", target}
            });
            return result;
        }
 
        switch (source.type())
        {
            case value_t::array:
            {
                // first pass: traverse common elements
                std::size_t i = 0;
 
                while (i < source.size() && i < target.size())
                {
                    // recursive call to compare array values at index i
                    auto temp_diff = diff(source[i], target[i], path + "/" + std::to_string(i));
                    result.insert(result.end(), temp_diff.begin(), temp_diff.end());
                    ++i;
                }
 
                // i now reached the end of at least one array
                // in a second pass, traverse the remaining elements
                // remove my remaining elements
                const auto end_index = static_cast<difference_type>(result.size());
 
                while (i < source.size())
                {
                    // add operations in reverse order to avoid invalid
                    // indices
                    result.insert(result.begin() + end_index, object(
                    {
                        {"op", "remove"},
                        {"path", path + "/" + std::to_string(i)}
                    }));
                    ++i;
                }
 
                // add other remaining elements
                while (i < target.size())
                {
                    result.push_back(
                    {
                        {"op", "add"},
                        {"path", path + "/-"},
                        {"value", target[i]}
                    });
                    ++i;
                }
 
                break;
            }
 
            case value_t::object:
            {
                // first pass: traverse this object's elements
                for (auto it = source.cbegin(); it != source.cend(); ++it)
                {
                    // escape the key name to be used in a JSON patch
                    const auto path_key = path + "/" + detail::escape(it.key());
 
                    if (target.find(it.key()) != target.end())
                    {
                        // recursive call to compare object values at key it
                        auto temp_diff = diff(it.value(), target[it.key()], path_key);
                        result.insert(result.end(), temp_diff.begin(), temp_diff.end());
                    }
 
                    else
                    {
                        // found a key that is not in o -> remove it
                        result.push_back(object(
                        {
                            {"op", "remove"}, {"path", path_key}
                        }));
                    }
                }
 
                // second pass: traverse other object's elements
                for (auto it = target.cbegin(); it != target.cend(); ++it)
                {
                    if (source.find(it.key()) == source.end())
                    {
                        // found a key that is not in this -> add it
                        const auto path_key = path + "/" + detail::escape(it.key());
                        result.push_back(
                        {
                            {"op", "add"}, {"path", path_key},
                            {"value", it.value()}
                        });
                    }
                }
 
                break;
            }
 
            case value_t::null:
            case value_t::string:
            case value_t::boolean:
            case value_t::number_integer:
            case value_t::number_unsigned:
            case value_t::number_float:
            case value_t::binary:
            case value_t::discarded:
            default:
            {
                // both primitive type: replace value
                result.push_back(
                {
                    {"op", "replace"}, {"path", path}, {"value", target}
                });
                break;
            }
        }
 
        return result;
    }