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

NJsonSchema for .NET

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NJsonSchema is a .NET library to read, generate and validate JSON Schema draft v4 schemas. The library can read a schema from a file or string and validate JSON data against it. A schema can also be generated from an existing .NET class. With the code generation APIs you can generate C# and TypeScript classes or interfaces from a schema.

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

NuGet packages:

The NuGet packages may require the Microsoft.NETCore.Portable.Compatibility package on .NET Core/UWP targets (if mscorlib is missing).

CI NuGet Feed: https://www.myget.org/gallery/njsonschema-ci

Features:

  • Read existing JSON Schemas and validate JSON data
  • Generate JSON Schema from .NET type via reflection (with support for many attributes/annotations)
  • Generate JSON Schema from sample JSON data
  • Support for schema references ($ref) (relative, URL and file)
  • Generate C# and TypeScript code from JSON Schema
  • Support for .NET Core (via PCL 259 / .NET Standard 1.0, also see XML Documentation)

NJsonSchema is heavily used in NSwag, a Swagger API toolchain for .NET which generates client code for Web API services. NSwag also provides command line tools to use the NJsonSchema's JSON Schema generator (command types2swagger).

The project is developed and maintained by Rico Suter and other contributors.

NJsonSchema usage

The JsonSchema4 class can be used as follows:

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

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

schema = await JsonSchema4.FromJsonAsync(schemaData);

The Person class:

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

    public string MiddleName { 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:

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "type": "object",
  "title": "Person",
  "additionalProperties": false,
  "required": [
    "FirstName",
    "LastName"
  ],
  "properties": {
    "FirstName": {
      "type": "string"
    },
    "MiddleName": {
      "type": [
        "null",
        "string"
      ]
    },
    "LastName": {
      "type": "string"
    },
    "Gender": {
      "oneOf": [
        {
          "$ref": "#/definitions/Gender"
        }
      ]
    },
    "NumberWithRange": {
      "type": "integer",
      "maximum": 5.0,
      "minimum": 2.0
    },
    "Birthday": {
      "type": "string",
      "format": "date-time"
    },
    "Company": {
      "oneOf": [
        {
          "$ref": "#/definitions/Company"
        },
        {
          "type": "null"
        }
      ]
    },
    "Cars": {
      "type": [
        "array",
        "null"
      ],
      "items": {
        "$ref": "#/definitions/Car"
      }
    }
  },
  "definitions": {
    "Gender": {
      "type": "integer",
      "x-enumNames": [
        "Male",
        "Female"
      ],
      "enum": [
        0,
        1
      ],
      "description": ""
    },
    "Company": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "Name": {
          "type": [
            "null",
            "string"
          ]
        }
      }
    },
    "Car": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "Name": {
          "type": [
            "null",
            "string"
          ]
        },
        "Manufacturer": {
          "oneOf": [
            {
              "$ref": "#/definitions/Company"
            },
            {
              "type": "null"
            }
          ]
        }
      }
    }
  }
}

NJsonSchema.CodeGeneration usage

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

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

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

The previously generated JSON Schema would generate the following TypeScript code:

export interface Person {
    FirstName: string;
    MiddleName?: string;
    LastName: string;
    Gender?: GenderAsInteger;
    NumberWithRange?: number;
    Birthday?: Date;
    Company?: Company;
    Cars?: Car[];
}

export enum GenderAsInteger
{
    Male = 0, 
    Female = 1, 
}

export interface Company {
    Name?: string;
}

export interface Car {
    Name?: string;
    Manufacturer?: Company;
}

Final notes

Applications which use the library:

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