NJsonSchema for .NET

NSwag | NJsonSchema | Apimundo | Namotion.Reflection

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 and Namotion.Reflection for additional .NET reflection APIs.

NuGet packages:

NJsonSchema : JSON Schema parsing, validation and generation classes
NJsonSchema.Annotations : JSON Schema annotations controlling serialization
NJsonSchema.Yaml : Read and write JSON Schemas from YAML
NJsonSchema.CodeGeneration : Base classes to generate code from a JSON Schema
NJsonSchema.CodeGeneration.CSharp : Generates CSharp classes
NJsonSchema.CodeGeneration.TypeScript : Generates TypeScript interfaces or classes

Preview NuGet Feed: https://www.myget.org/F/njsonschema/api/v3/index.json

Features:

Read existing JSON Schemas and validate JSON data (JsonSchema.FromJsonAsync())
Generate JSON Schema from .NET type via reflection (with support for many attributes/annotations) (JsonSchema.FromType<MyType>())
Generate JSON Schema from sample JSON data (JsonSchema.FromSampleJson())
Support for schema references ($ref) (relative, URL and file)
Generate C# and TypeScript code from JSON Schema
Supports .NET Standard 2.0, also see XML Documentation)
Supports JSON Schema, Swagger and OpenAPI DTO schemas

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.

Some code generators can directly be used via the Apimundo service.

NJsonSchema usage

The JsonSchema class can be used as follows:

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

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

schema = await JsonSchema.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:

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "title": "Person",
  "type": "object",
  "additionalProperties": false,
  "required": [
    "FirstName",
    "LastName"
  ],
  "properties": {
    "FirstName": {
      "type": "string",
      "minLength": 1
    },
    "MiddleName": {
      "type": [
        "null",
        "string"
      ]
    },
    "LastName": {
      "type": "string",
      "minLength": 1
    },
    "Gender": {
      "$ref": "#/definitions/Gender"
    },
    "NumberWithRange": {
      "type": "integer",
      "format": "int32",
      "maximum": 5.0,
      "minimum": 2.0
    },
    "Birthday": {
      "type": "string",
      "format": "date-time"
    },
    "Company": {
      "oneOf": [
        {
          "type": "null"
        },
        {
          "$ref": "#/definitions/Company"
        }
      ]
    },
    "Cars": {
      "type": [
        "array",
        "null"
      ],
      "items": {
        "$ref": "#/definitions/Car"
      }
    }
  },
  "definitions": {
    "Gender": {
      "type": "integer",
      "description": "",
      "x-enumNames": [
        "Male",
        "Female"
      ],
      "enum": [
        0,
        1
      ]
    },
    "Company": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "Name": {
          "type": [
            "null",
            "string"
          ]
        }
      }
    },
    "Car": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "Name": {
          "type": [
            "null",
            "string"
          ]
        },
        "Manufacturer": {
          "oneOf": [
            {
              "type": "null"
            },
            {
              "$ref": "#/definitions/Company"
            }
          ]
        }
      }
    }
  }
}

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.

TypeScript

The previously generated JSON Schema would generate the following TypeScript interfaces.

Settings:

new TypeScriptGeneratorSettings { TypeStyle = TypeScriptTypeStyle.Interface, TypeScriptVersion = 4.3m }

Output:

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

export interface Company {
    Name: string | undefined;
}

export interface Car {
    Name: string | undefined;
    Manufacturer: Company | undefined;
}

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

... and the following TypeScript classes.

Settings:

new TypeScriptGeneratorSettings { TypeStyle = TypeScriptTypeStyle.Class, TypeScriptVersion = 4.3m }

Output:

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

export class Company implements ICompany {
    name: string | undefined;

    constructor(data?: ICompany) {
        if (data) {
            for (var property in data) {
                if (data.hasOwnProperty(property))
                    (<any>this)[property] = (<any>data)[property];
            }
        }
    }

    init(data?: any) {
        if (data) {
            this.name = data["Name"];
        }
    }

    static fromJS(data: any): Company {
        let result = new Company();
        result.init(data);
        return result;
    }

    toJSON(data?: any) {
        data = typeof data === 'object' ? data : {};
        data["Name"] = this.name;
        return data; 
    }
}

export interface ICompany {
    name: string | undefined;
}

export class Car implements ICar {
    name: string | undefined;
    manufacturer: Company | undefined;

    constructor(data?: ICar) {
        if (data) {
            for (var property in data) {
                if (data.hasOwnProperty(property))
                    (<any>this)[property] = (<any>data)[property];
            }
        }
    }

    init(data?: any) {
        if (data) {
            this.name = data["Name"];
            this.manufacturer = data["Manufacturer"] ? Company.fromJS(data["Manufacturer"]) : <any>undefined;
        }
    }

    static fromJS(data: any): Car {
        let result = new Car();
        result.init(data);
        return result;
    }

    toJSON(data?: any) {
        data = typeof data === 'object' ? data : {};
        data["Name"] = this.name;
        data["Manufacturer"] = this.manufacturer ? this.manufacturer.toJSON() : <any>undefined;
        return data; 
    }
}

export interface ICar {
    name: string | undefined;
    manufacturer: Company | undefined;
}

export class Person implements IPerson {
    firstName: string;
    middleName: string | undefined;
    lastName: string;
    gender: Gender;
    numberWithRange: number;
    birthday: Date;
    company: Company | undefined;
    cars: Car[] | undefined;

    constructor(data?: IPerson) {
        if (data) {
            for (var property in data) {
                if (data.hasOwnProperty(property))
                    (<any>this)[property] = (<any>data)[property];
            }
        }
    }

    init(data?: any) {
        if (data) {
            this.firstName = data["FirstName"];
            this.middleName = data["MiddleName"];
            this.lastName = data["LastName"];
            this.gender = data["Gender"];
            this.numberWithRange = data["NumberWithRange"];
            this.birthday = data["Birthday"] ? new Date(data["Birthday"].toString()) : <any>undefined;
            this.company = data["Company"] ? Company.fromJS(data["Company"]) : <any>undefined;
            if (data["Cars"] && data["Cars"].constructor === Array) {
                this.cars = [];
                for (let item of data["Cars"])
                    this.cars.push(Car.fromJS(item));
            }
        }
    }

    static fromJS(data: any): Person {
        let result = new Person();
        result.init(data);
        return result;
    }

    toJSON(data?: any) {
        data = typeof data === 'object' ? data : {};
        data["FirstName"] = this.firstName;
        data["MiddleName"] = this.middleName;
        data["LastName"] = this.lastName;
        data["Gender"] = this.gender;
        data["NumberWithRange"] = this.numberWithRange;
        data["Birthday"] = this.birthday ? this.birthday.toISOString() : <any>undefined;
        data["Company"] = this.company ? this.company.toJSON() : <any>undefined;
        if (this.cars && this.cars.constructor === Array) {
            data["Cars"] = [];
            for (let item of this.cars)
                data["Cars"].push(item.toJSON());
        }
        return data; 
    }
}

export interface IPerson {
    firstName: string;
    middleName: string | undefined;
    lastName: string;
    gender: Gender;
    numberWithRange: number;
    birthday: Date;
    company: Company | undefined;
    cars: Car[] | undefined;
}

NJsonSchema.SampleJsonSchemaGenerator usage

The NJsonSchema.SampleJsonSchemaGenerator can be used to generate a JSON Schema from sample JSON data:

JSON Schema Specification

By default, the NJsonSchema.SampleJsonSchemaGenerator generates a JSON Schema based on the JSON Schema specification. See: JSON Schema Specification

var generator = new SampleJsonSchemaGenerator(new SampleJsonSchemaGeneratorSettings());

var schema = generator.Generate("{...}");

Input:

{
  "int": 1,
  "float": 340282346638528859811704183484516925440.0,
  "str": "abc",
  "bool": true,
  "date": "2012-07-19",
  "datetime": "2012-07-19 10:11:11",
  "timespan": "10:11:11"
}

Output:

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "type": "object",
  "properties": {
    "int": {
      "type": "integer"
    },
    "float": {
      "type": "number"
    },
    "str": {
      "type": "string"
    },
    "bool": {
      "type": "boolean"
    },
    "date": {
      "type": "string",
      "format": "date"
    },
    "datetime": {
      "type": "string",
      "format": "date-time"
    },
    "timespan": {
      "type": "string",
      "format": "duration"
    }
  }
}

OpenApi Specification

To generate a JSON Schema for OpenApi, provide the SchemaType.OpenApi3 in the settings. See: OpenApi Specification

var generator = new SampleJsonSchemaGenerator(new SampleJsonSchemaGeneratorSettings { SchemaType = SchemaType.OpenApi3 });

var schema = generator.Generate("{...}");

Input:

{
  "int": 12345,
  "long": 1736347656630,
  "float": 340282346638528859811704183484516925440.0,
  "double": 340282346638528859811704183484516925440123456.0,
}

Output:

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "type": "object",
  "properties": {
    "int": {
      "type": "integer",
      "format": "int32"
    },
    "long": {
      "type": "integer",
      "format": "int64"
    },
    "float": {
      "type": "number",
      "format": "float"
    },
    "double": {
      "type": "number",
      "format": "double"
    }
  }
}

Final notes

Applications which use the library:

VisualJsonEditor, a JSON schema based file editor for Windows.
NSwag: The Swagger API toolchain for .NET
SigSpec for SignalR Core: Specification and code generator for SignalR Core.

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NJsonSchema for .NET

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