json_schema_validate.cpp

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#include <iostream>
#include <iomanip>
 
#include <nlohmann/json-schema.hpp>
 
using nlohmann::json;
using nlohmann::json_schema::json_validator;
 
// The schema is defined based upon a string literal
static json person_schema = R"(
{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "title": "A person",
    "properties": {
        "name": {
            "description": "Name",
            "type": "string"
        },
        "age": {
            "description": "Age of the person",
            "type": "number",
            "minimum": 2,
            "maximum": 200
        }
    },
    "required": [
                 "name",
                 "age"
                 ],
    "type": "object"
}
 
)"_json;
 
// The people are defined with brace initialization
static json bad_person = {{"age", 42}};
static json good_person = {{"name", "Albert"}, {"age", 42}};
 
int main()
{
    /* json-parse the schema */
 
    json_validator validator; // create validator
 
    try {
        validator.set_root_schema(person_schema); // insert root-schema
    } catch (const std::exception &e) {
        std::cerr << "Validation of schema failed, here is why: " << e.what() << "\n";
        return EXIT_FAILURE;
    }
 
    /* json-parse the people - API of 1.0.0, default throwing error handler */
 
    for (auto &person : {bad_person, good_person}) {
        std::cout << "About to validate this person:\n"
                  << std::setw(2) << person << std::endl;
        try {
            validator.validate(person); // validate the document - uses the default throwing error-handler
            std::cout << "Validation succeeded\n";
        } catch (const std::exception &e) {
            std::cerr << "Validation failed, here is why: " << e.what() << "\n";
        }
    }
 
    /* json-parse the people - with custom error handler */
    // class custom_error_handler : public nlohmann::json_schema::basic_error_handler
    // {
    //     void error(const nlohmann::json_pointer<nlohmann::basic_json<>> &pointer, const json &instance,
    //         const std::string &message) override
    //     {
    //         nlohmann::json_schema::basic_error_handler::error(pointer, instance, message);
    //         std::cerr << "ERROR: '" << pointer << "' - '" << instance << "': " << message << "\n";
    //     }
    // };
 
 
    // for (auto &person : {bad_person, good_person}) {
    //     std::cout << "About to validate this person:\n"
    //               << std::setw(2) << person << std::endl;
 
    //     custom_error_handler err;
    //     validator.validate(person, err); // validate the document
 
    //     if (err)
    //         std::cerr << "Validation failed\n";
    //     else
    //         std::cout << "Validation succeeded\n";
    // }
 
    return EXIT_SUCCESS;
}