NJsonSchema for .NET

JSON Schema draft v4 reader, generator and validator for .NET

NuGet packages:

• NJsonSchema: JSON Schema 4 validation and parsing classes
• NJsonSchema.CodeGeneration: Classes to generate code from a JSON Schema 4 (C# and TypeScript)

The library uses Json.NET to read and write JSON data.

Features:

• Read existing JSON Schemas and validate JSON data
• Generate JSON Schema from .NET type via reflection (with support for many attributes/annotations)
• Support for schema references ($ref) (relative, URL and file)
• Generate C# and TypeScript code from JSON Schema

NJsonSchema is heavily used in NSwag, a Swagger API toolchain for .NET which generates client code for Web API services.

NJsonSchema usage

The JsonSchema4 class can be used as follows:

var schema = JsonSchema4.FromType<Person>();
var schemaData = schema.ToJson();
var errors = schema.Validate("{...}");

foreach (var error in errors)
    Console.WriteLine(error.Path + ": " + error.Kind);

schema = JsonSchema4.FromJson(schemaData);

The Person class:

public class Person
{
    [Required]
    public string FirstName { get; set; }

    [Required]
    public string LastName { get; set; }

    public Gender Gender { get; set; }

    [Range(2, 5)]
    public int NumberWithRange { get; set; }

    public DateTime Birthday { get; set; }

    public Company Company { get; set; }

    public Collection<Car> Cars { get; set; }
}

public enum Gender
{
    Male,
    Female
}

public class Car
{
    public string Name { get; set; }

    public Company Manufacturer { get; set; }
}

public class Company
{
    public string Name { get; set; }
}

The generated JSON schema data stored in the schemaData variable:

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "typeName": "Person",
  "type": "object",
  "required": [
    "FirstName",
    "LastName",
    "Gender",
    "NumberWithRange",
    "Birthday"
  ],
  "properties": {
    "FirstName": {
      "type": "string"
    },
    "LastName": {
      "type": "string"
    },
    "Gender": {
      "type": "string",
      "enum": [
        "Male",
        "Female"
      ]
    },
    "NumberWithRange": {
      "type": "integer",
      "maximum": 5.0,
      "minimum": 2.0
    },
    "Birthday": {
      "type": "string",
      "format": "date-time"
    },
    "Company": {
      "typeName": "Company",
      "type": "object",
      "properties": {
        "Name": {
          "type": "string"
        }
      }
    },
    "Cars": {
      "items": {
        "typeName": "Car",
        "type": "object",
        "properties": {
          "Name": {
            "type": "string"
          },
          "Manufacturer": {
            "typeName": "Company",
            "type": "object",
            "$ref": "#/properties/Company"
          }
        }
      },
      "type": "array"
    }
  }
}

NJsonSchema.CodeGeneration usage

The NJsonSchema.CodeGeneration can be used to generate C# or TypeScript code from a JSON schema:

var generator new CSharpClassGenerator(schema);
var file = generator.GenerateFile();

The file variable now contains the C# code for all the classes defined in the JSON schema.

Final notes

Applications which use the library:

• VisualJsonEditor, a JSON schema based file editor for Windows.
• NSwag: The Swagger API toolchain for .NET