Validate JSON against JSON Schema C#

Question

Is there a way to validate a JSON structure against a JSON schema for that structure? I have looked and found JSON.Net validate but this does not do what I want.

JSON.net does:

JsonSchema schema = JsonSchema.Parse(@"{
  'type': 'object',
  'properties': {
    'name': {'type':'string'},
    'hobbies': {'type': 'array'}
  }
}");

JObject person = JObject.Parse(@"{
  'name': 'James',
  'hobbies': ['.NET', 'LOLCATS']
}");

bool valid = person.IsValid(schema);
// true

This validates to true.

JsonSchema schema = JsonSchema.Parse(@"{
  'type': 'object',
  'properties': {
    'name': {'type':'string'},
    'hobbies': {'type': 'array'}
  }
}");

JObject person = JObject.Parse(@"{
  'surname': 2,
  'hobbies': ['.NET', 'LOLCATS']
}");

bool valid = person.IsValid(schema);

This also validates to true

JsonSchema schema = JsonSchema.Parse(@"{
  'type': 'object',
  'properties': {
    'name': {'type':'string'},
    'hobbies': {'type': 'array'}
  }
}");

JObject person = JObject.Parse(@"{
  'name': 2,
  'hobbies': ['.NET', 'LOLCATS']
}");

bool valid = person.IsValid(schema);

Only this validates to false.

Ideally I would like it to Validate that there are no fields aka name in there that shouldn't be in there aka surname.

Answer 1

I think that you just need to add

'additionalProperties': false

to your schema. This will stop unknown properties being provided.

So now your results will be:- True, False, False

test code....

void Main()
{
var schema = JsonSchema.Parse(
@"{
    'type': 'object',
    'properties': {
        'name': {'type':'string'},
        'hobbies': {'type': 'array'}
    },
    'additionalProperties': false
    }");

IsValid(JObject.Parse(
@"{
    'name': 'James',
    'hobbies': ['.NET', 'LOLCATS']
  }"), 
schema).Dump();

IsValid(JObject.Parse(
@"{
    'surname': 2,
    'hobbies': ['.NET', 'LOLCATS']
  }"), 
schema).Dump();

IsValid(JObject.Parse(
@"{
    'name': 2,
    'hobbies': ['.NET', 'LOLCATS']
  }"), 
schema).Dump();
}

public bool IsValid(JObject obj, JsonSchema schema)
{
    return obj.IsValid(schema);
}

output :-

True
False
False

You could also add "required":true to the fields that must be supplied that way you can return a message with details of missing/invalid fields:-

Property 'surname' has not been defined and the schema does not allow additional     properties. Line 2, position 19. 
Required properties are missing from object: name. 

Invalid type. Expected String but got Integer. Line 2, position 18. 

Answer 2

Ok i hope this will help.

This is your schema:

 public class test
{
    public string Name { get; set; }
    public string ID { get; set; }

}

This is your validator:

/// <summary>
    /// extension that validates if Json string is copmplient to TSchema.
    /// </summary>
    /// <typeparam name="TSchema">schema</typeparam>
    /// <param name="value">json string</param>
    /// <returns>is valid?</returns>
    public static bool IsJsonValid<TSchema>(this string value)
        where TSchema : new()
    {
        bool res = true;
        //this is a .net object look for it in msdn
        JavaScriptSerializer ser = new JavaScriptSerializer();
        //first serialize the string to object.
        var obj = ser.Deserialize<TSchema>(value);

        //get all properties of schema object
        var properties = typeof(TSchema).GetProperties();
        //iterate on all properties and test.
        foreach (PropertyInfo info in properties)
        {
            // i went on if null value then json string isnt schema complient but you can do what ever test you like her.
            var valueOfProp = obj.GetType().GetProperty(info.Name).GetValue(obj, null);
            if (valueOfProp == null)
                res = false;
        }

        return res;
    }

And how to use is:

string json = "{Name:'blabla',ID:'1'}";
        bool res = json.IsJsonValid<test>();

If you have any question please ask, hope this helps, please take into consideration that this isn't a complete code without exception handling and such...

Answer 3

I am just adding short answer, using JSchemaGenerator from Newtonsoft.Json.Schema

 public static bool IsJsonValid<TSchema>>(string value)
    {
        JSchemaGenerator generator = new JSchemaGenerator();
        JSchema schema = generator.Generate(typeof(TSchema));
        schema.AllowAdditionalProperties = false;           

        JObject obj = JObject.Parse(value);
        return obj.IsValid(schema);
    }

Answer 4

public static class RequestSchema
{ 
    public static bool Validate<T>(string requestBody)
    {
        JSchemaGenerator generator = new JSchemaGenerator();
        JSchema schema = generator.Generate(typeof(T));
        JObject jsonObject = JObject.Parse(requestBody);
        bool isValid = jsonObject.IsValid(schema);
        return isValid;
    }
}

And call Method
RequestSchema.Validate<Person>(requestBody)

Reference https://www.newtonsoft.com/jsonschema