Can I convert json or struct into JSON schema?

[recsater]

I want to create a basic JSON schema from a struct or a jsoncons::json. Is there already a function for this? If not, could you provide ideas on how I can implement it myself?

[danielaparker]

We don't currently provide any support for that, and I haven't really thought about it. It's something we could look at as a new feature, but not likely any time soon. Our current focus with JSON Schema is on completing support for drafts 2019-09 and 2020-12.

[danielaparker]

Here's some code to get you started.

#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonschema/jsonschema.hpp>
#include <iostream>

using namespace jsoncons;
namespace jsonschema = jsoncons::jsonschema;

void generate_type_keyword(const json& value, json_string_encoder& encoder)
{
    switch (value.type())
    {
    case json_type::object_value:
        encoder.key("type");
        encoder.string_value("object");

        encoder.key("properties");
        encoder.begin_object();
        for (const auto& member : value.object_range())
        {
            encoder.key(member.key());
            encoder.begin_object();
            generate_type_keyword(member.value(), encoder);
            encoder.end_object();
        }
        encoder.end_object();
        break;
    case json_type::string_value:
        encoder.key("type");
        encoder.string_value("string");
        break;
    default:
        break;
    }
}

void generate_schema(const json& data, json_string_encoder& encoder)
{
    encoder.begin_object();
    encoder.key("schema");
    encoder.string_value("https://json-schema.org/draft/2020-12/schema");  
    encoder.key("id");
    encoder.string_value("https://example.com/foo");

    generate_type_keyword(data, encoder);

    encoder.end_object();
    encoder.flush();
}

int main()
{
    std::string data_str = R"(
{
    "foo" : {"bar" : "baz"}
}
)";

    json data = json::parse(data_str);

    std::string buffer;
    json_string_encoder encoder(buffer);

    generate_schema(data, encoder);

    std::cout << buffer << "\n";

    // A quick test, using code from master branch with preliminary draft 2020-12 support
    json schema_document = json::parse(buffer);
    auto schema = jsonschema::make_schema(schema_document);
    jsonschema::json_validator validator(schema);
    std::cout << "Is valid: " << validator.is_valid(data) << "\n";
}

Output:

{
    "schema": "https://json-schema.org/draft/2020-12/schema",
    "id": "https://example.com/foo",
    "type": "object",
    "properties": {
        "foo": {
            "type": "object",
            "properties": {
                "bar": {
                    "type": "string"
                }
            }
        }
    }
}
Is valid: 1

[recsater]

thx so much ❤️