ClickHouse/src/Functions/visitParamExtractString.cpp

#include <Functions/FunctionFactory.h>
#include <Functions/FunctionsVisitParam.h>
#include <Functions/FunctionsStringSearchToString.h>


namespace DB
{

struct ExtractString
{
    static void extract(const UInt8 * pos, const UInt8 * end, ColumnString::Chars & res_data)
    {
        size_t old_size = res_data.size();
        ReadBufferFromMemory in(pos, end - pos);
        if (!tryReadJSONStringInto(res_data, in))
            res_data.resize(old_size);
    }
};

struct NameSimpleJSONExtractString { static constexpr auto name = "simpleJSONExtractString"; };
using FunctionSimpleJSONExtractString = FunctionsStringSearchToString<ExtractParamToStringImpl<ExtractString>, NameSimpleJSONExtractString>;

REGISTER_FUNCTION(VisitParamExtractString)
{
    factory.registerFunction<FunctionSimpleJSONExtractString>(FunctionDocumentation{
        .description = R"(Parses String in double quotes from the value of the field named field_name.

        There is currently no support for code points in the format \uXXXX\uYYYY that are not from the basic multilingual plane (they are converted to CESU-8 instead of UTF-8).)",
        .syntax = "simpleJSONExtractString(json, field_name)",
        .arguments
        = {{"json", "The JSON in which the field is searched for. String."},
           {"field_name", "The name of the field to search for. String literal."}},
        .returned_value = "It returns the value of a field as a String, including separators. The value is unescaped. It returns an empty "
                          "String: if the field doesn't contain a double quoted string, if unescaping fails or if the field doesn't exist.",
        .examples
        = {{.name = "simple",
            .query = R"(CREATE TABLE jsons
(
    json String
)
ENGINE = Memory;

INSERT INTO jsons VALUES ('{"foo":"\\n\\u0000"}');
INSERT INTO jsons VALUES ('{"foo":"\\u263"}');
INSERT INTO jsons VALUES ('{"foo":"\\u263a"}');
INSERT INTO jsons VALUES ('{"foo":"hello}');

SELECT simpleJSONExtractString(json, 'foo') FROM jsons ORDER BY json;)",
            .result = R"(\n\0

☺
)"}},
        .categories{"JSON"}});
    factory.registerAlias("visitParamExtractString", "simpleJSONExtractString");
}

}