ClickHouse/src/Functions/jsonMergePatch.cpp

#include <Columns/ColumnString.h>
#include <DataTypes/DataTypeString.h>
#include <Functions/FunctionFactory.h>
#include <Functions/FunctionHelpers.h>
#include <Functions/IFunction.h>
#include <Interpreters/Context.h>
#include <IO/ReadBufferFromString.h>
#include <Common/FieldVisitorToString.h>
#include "config.h"

#if USE_RAPIDJSON

#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
#include "rapidjson/filewritestream.h"
#include "rapidjson/prettywriter.h"
#include "rapidjson/filereadstream.h"


namespace DB
{

namespace ErrorCodes
{
    extern const int BAD_ARGUMENTS;
    extern const int ILLEGAL_COLUMN;
    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
}

namespace
{
    // select jsonMergePatch('{"a":1}','{"name": "joey"}','{"name": "tom"}','{"name": "zoey"}');
    //           ||
    //           \/
    // ┌───────────────────────┐
    // │ {"a":1,"name":"zoey"} │
    // └───────────────────────┘
    class FunctionjsonMergePatch : public IFunction
    {
    public:
        static constexpr auto name = "jsonMergePatch";
        static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionjsonMergePatch>(); }

        String getName() const override { return name; }
        bool isVariadic() const override { return true; }
        bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return true; }

        size_t getNumberOfArguments() const override { return 0; }
        bool useDefaultImplementationForConstants() const override { return true; }

        DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
        {
            if (arguments.empty())
                throw Exception(ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH, "Function {} requires at least one argument.", getName());

            for (const auto & arg : arguments)
                if (!isString(arg.type))
                    throw Exception(ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT, "Function {} requires string arguments", getName());

            return std::make_shared<DataTypeString>();
        }

        ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t input_rows_count) const override
        {
            chassert(!arguments.empty());

            rapidjson::Document::AllocatorType allocator;
            std::function<void(rapidjson::Value &, const rapidjson::Value &)> merge_objects;

            merge_objects = [&merge_objects, &allocator](rapidjson::Value & dest, const rapidjson::Value & src) -> void
            {
                if (!src.IsObject())
                    return;

                for (auto it = src.MemberBegin(); it != src.MemberEnd(); ++it)
                {
                    rapidjson::Value key(it->name, allocator);
                    rapidjson::Value value(it->value, allocator);
                    if (dest.HasMember(key))
                    {
                        if (dest[key].IsObject() && value.IsObject())
                            merge_objects(dest[key], value);
                        else
                            dest[key] = value;
                    }
                    else
                    {
                        dest.AddMember(key, value, allocator);
                    }
                }
            };

            auto parse_json_document = [](const ColumnString & column, rapidjson::Document & document, size_t i)
            {
                auto str_ref = column.getDataAt(i);
                const char * json = str_ref.data;

                document.Parse(json);
                if (document.HasParseError() || !document.IsObject())
                    throw Exception(ErrorCodes::BAD_ARGUMENTS, "Wrong JSON string to merge. Expected JSON object");
            };

            const auto * first_string = typeid_cast<const ColumnString *>(arguments[0].column.get());
            if (!first_string)
                throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Arguments of function {} must be strings", getName());

            std::vector<rapidjson::Document> merged_jsons;
            merged_jsons.reserve(input_rows_count);

            for (size_t i = 0; i < input_rows_count; ++i)
            {
                auto & merged_json = merged_jsons.emplace_back(rapidjson::Type::kObjectType, &allocator);
                parse_json_document(*first_string, merged_json, i);
            }

            for (size_t col_idx = 1; col_idx < arguments.size(); ++col_idx)
            {
                const auto * column_string = typeid_cast<const ColumnString *>(arguments[col_idx].column.get());
                if (!column_string)
                    throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Arguments of function {} must be strings", getName());

                for (size_t i = 0; i < input_rows_count; ++i)
                {
                    rapidjson::Document document(&allocator);
                    parse_json_document(*column_string, document, i);
                    merge_objects(merged_jsons[i], document);
                }
            }

            auto result = ColumnString::create();
            auto & result_string = assert_cast<ColumnString &>(*result);
            rapidjson::CrtAllocator buffer_allocator;

            for (size_t i = 0; i < input_rows_count; ++i)
            {
                rapidjson::StringBuffer buffer(&buffer_allocator);
                rapidjson::Writer<rapidjson::StringBuffer> writer(buffer);

                merged_jsons[i].Accept(writer);
                result_string.insertData(buffer.GetString(), buffer.GetSize());
            }

            return result;
        }
    };

}

REGISTER_FUNCTION(jsonMergePatch)
{
    factory.registerFunction<FunctionjsonMergePatch>(FunctionDocumentation{
        .description="Returns the merged JSON object string, which is formed by merging multiple JSON objects."});
}

}

#endif