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### Custom Error Messages (since 1.2.0)
jsoncons optionally allows schema authors to provide custom error messages via an `errorMessage` keyword.
To enable this feature, you need to provide an `expression_options` argument with `enable_custom_error_message` set to `true` when preparing a JSON Schema document with `make_json_schema`.
The `errorMessage` keyword can be set to either
- A string that represents a custom message, or
- An object that maps message keys to custom messages
An example of an object that maps message keys to custom messages is
```json
{
"maxItems" : "At most 3 numbers are allowed in 'foo'",
"type" : "Only numbers are allowed in 'foo'",
"format.date": "Date format must be YYYY-MM-DD"
}
```
Maps are visible in the lexical scope of a schema. Message keys are JSON Schema keywords, except for `format`, where they have the form
format.<format value>
This implementation of key-message maps draws on the experience of [networknt json-schema-validator](https://github.com/networknt/json-schema-validator/blob/master/doc/cust-msg.md). We do not currently support parameterized messages.
### Example
```cpp
#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonschema/jsonschema.hpp>
#include <iostream>
namespace jsonschema = jsoncons::jsonschema;
int main()
{
std::string schema_str = R"(
{
"type": "object",
"properties": {
"date": {
"type": "string",
"format": "date"
},
"foo": {
"type": "array",
"maxItems": 3,
"items" : {
"type" : "number"
},
"errorMessage" : {
"maxItems" : "At most 3 numbers are allowed in 'foo'",
"type" : "Only numbers are allowed in 'foo'"
}
},
"bar": {
"type": "string",
"errorMessage" : "Type of `bar` must be string"
}
},
"errorMessage": {
"format.date": "Date format must be YYYY-MM-DD"
}
}
)";
auto options = jsonschema::evaluation_options{}
.enable_custom_error_message(true)
.require_format_validation(true);
auto schema = jsoncons::json::parse(schema_str);
auto compiled = jsonschema::make_json_schema<jsoncons::json>(schema, options);
std::string data_str = R"(
{
"foo": [1, 2, "three"],
"bar": 123,
"date": "05-13-1955"
}
)";
auto data = jsoncons::json::parse(data_str);
std::vector<std::string> messages;
auto reporter = [&](const jsonschema::validation_message& msg) -> jsonschema::walk_result
{
messages.push_back(msg.message());
return jsonschema::walk_result::advance;
};
compiled.validate(data, reporter);
for (const auto& msg : messages)
{
std::cout << msg << "\n";
}
}
```
Output:
```
Type of `bar` must be string
Date format must be YYYY-MM-DD
Only numbers are allowed in 'foo'
```
|
