JSON Schema - unique pattern properties

Question

I want to create a JSON Schema that allows properties with names that are arbitrary, but unique.

I have been trying to do this with patternProperties, but it seems to allow duplicate property names.

For example, the following schema:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "patternProperties": {
                "^.*$": {
                    "type": "string"
                }
            },
            "additionalProperties": false
}

Validates this JSON:

{
  "property1" : "value1",
  "property2" : "value2",
  "property1" : "value3"
}

But I want it to fail because the 1st and 3rd property have the same name. How can I do that?

Answer 1

IMHO...

JSON Schema doesn't have any validation to detect duplicate properties in a JSON object.

The JSON spec doesn't make any mention of duplicate properties so they are valid but not recommended.

to check on duplicated names:

void Main()
{
    try
    {
        JsonSchema schema = JsonSchema.Parse(@"{
  '$schema': 'https://json-schema.org/draft/2020-12/schema',
    'type': 'object',
    'patternProperties': {
                '^.*$': {
                    'type': 'string'
                }
            },
            'additionalProperties': false
    }");


        JObject o = JObject.Parse("{\"property1\":\"value1\",\"property2\":\"value2\",\"property1\":\"value3\"}", new JsonLoadSettings
        {
            DuplicatePropertyNameHandling = DuplicatePropertyNameHandling.Error
        });

        bool valid = o.IsValid(schema).Dump();
        // true
    }
    catch (JsonReaderException ex)
    {
        Console.Write($"Invalid json file, {ex.Message}.");
    }
}

the exception would be :

[Invalid json file, Property with the name 'property1' already exists in the current JSON object. Path 'property1', line 1, position 55..]