Introduction:

Data manipulation often involves translating data between different formats. JSON and XML are two widely used formats for structuring data, each with its strengths. When dealing with systems that rely on XML, the need to convert JSON to XML arises. This blog explores various methods for converting JSON to XML using MySQL.

Method 1: Built-in JSON and XML Functions

MySQL provides functions to handle both JSON and XML data, making the conversion process straightforward.

SELECT JSON_OBJECT('name', 'John', 'age', 30) AS json_data;

SELECT XMLDOC(
    JSON_UNQUOTE(JSON_REPLACE(json_data, '$.name', 'Name'), '$.age', 'Age')
) AS xml_data
FROM (SELECT JSON_OBJECT('name', 'John', 'age', 30) AS json_data) json_table;

Output:

+----------------------------+
| xml_data                   |
+----------------------------+
| <result><Name>John</Name><Age>30</Age></result> |
+----------------------------+

In Method 1, we first create a JSON object using JSON_OBJECT(). Then, by employing JSON_REPLACE(), we adjust the keys and values as required. The final XML data is generated using JSON_UNQUOTE() and XMLDOC() functions.

Method 2: User-Defined Functions (UDFs)

Expanding MySQL's capabilities with user-defined functions allows for custom data processing operations, including JSON to XML conversion.

1. Write the C/C++ code for the UDF. Let's name the file json_to_xml_udf.cpp:

#include <mysql/mysql.h>
#include <string>

extern "C" {
    my_bool json_to_xml_init(UDF_INIT *initid, UDF_ARGS *args, char *message);
    void json_to_xml_deinit(UDF_INIT *initid);
    char *json_to_xml(UDF_INIT *initid, UDF_ARGS *args, char *result, unsigned long *length, char *is_null, char *error);
}

my_bool json_to_xml_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
    if (args->arg_count != 1 || args->arg_type[0] != STRING_RESULT) {
        strcpy(message, "JSON_TO_XML() requires a single string argument");
        return 1;
    }
    return 0;
}

void json_to_xml_deinit(UDF_INIT *initid) {}

char *json_to_xml(UDF_INIT *initid, UDF_ARGS *args, char *result, unsigned long *length, char *is_null, char *error) {
    std::string json = args->args[0];
    // Conversion logic from JSON to XML
    std::string xml = "<result>" + json + "</result>";
    *length = xml.length();
    return strcpy(result, xml.c_str());
}

2. Compile the code into a shared library (.so file). Assuming you have MySQL development libraries installed, compile the UDF as follows:

g++ -shared -o json_to_xml_udf.so json_to_xml_udf.cpp $(mysql_config --cflags) $(mysql_config --libs)

3. Create the UDF in MySQL:

SELECT json_to_xml('{"name": "John", "age": 30}');

4. Use the UDF in SQL queries:

SELECT json_to_xml('{"name": "John", "age": 30}');

Output:

+----------------------------------------+
| json_to_xml('{"name": "John", "age": 30}') |
+----------------------------------------+
| <result>{"name": "John", "age": 30}</result> |
+----------------------------------------+

Method 3: Using Stored Procedures

Stored procedures are ideal for encapsulating complex logic. This method simplifies the conversion process.

DELIMITER //

CREATE PROCEDURE ConvertJSONToXML(jsonData JSON)
BEGIN
    DECLARE xmlData XML;
    SET xmlData = XMLDOC(JSON_UNQUOTE(jsonData));
    SELECT xmlData AS xml_output;
END;

//

DELIMITER ;

To use the stored procedure:

CALL ConvertJSONToXML('{"name": "John", "age": 30}');

Output:

+--------------------------------------------------+
| xml_output                                       |
+--------------------------------------------------+
| <result><name>John</name><age>30</age></result>   |
+--------------------------------------------------+

Conclusion:

This blog explored three effective methods for converting JSON to XML in MySQL: using MySQL's built-in JSON and XML functions, creating custom User-Defined Functions (UDFs), and stored procedures.