JsonApiNet

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An easy-to-use, extensible C# library for JSON API documents.

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JsonApiNet
---

An easy-to-use, extensible C# library for JSON API documents.

- Deserialization of complex attributes
- Compound document support for included resources
- Extensible `Type` and `Property` resolution with intelligent defaults
- Attribute and relationship mapping
- Full object graph for the JSON API document
- And more!

Written against **v1.0** of [the JSON API specification](http://jsonapi.org/format/)

Built on top of [Json.NET](https://github.com/JamesNK/Newtonsoft.Json) and also uses [Humanizer](https://github.com/MehdiK/Humanizer) for type and property inference.

> Note: This library doesn't provide a serializer (yet). There are a couple alternative serializers for JSON API out there, such as the [JsonApiMediaTypeFormatter](https://github.com/rmichela/JsonApiMediaTypeFormatter). I haven't done a ton of exploration in this area yet, but I would eventually like to extend this library to support both serialization and deserialization. If you're the author of one of these libraries and think it'd be a good fit to merge with this project, let me know.

Getting Started
---

`JsonApiNet` is available on `NuGet` ([See package details on nuget.org](https://www.nuget.org/packages/JsonApiNet/2.0.0))

Install-Package JsonApiNet

Single Resource
---

Here is a trivial, single-resource, JSON API document:

{
      "data": {
        "type": "articles",
        "id": "30cd428f-1a3b-459b-a9a8-0ca87c14dd31",
        "attributes": {
          "title": "JSON API paints my bikeshed!"
        }
      }
    }

And we want to parse this response into an `Article` class:

public class Article {
        public Guid Id { get; set; }
        public string Title { get; set; }
    }

We do so by calling `ResourceFromDocument<T>`:

var article = JsonApi.ResourceFromDocument<Article>(json);
    Assert.AreEqual("JSON API paints my bikeshed!", article.Title);

Multiple Resources
---
Consider this collection (it's the same as the previous example, except `"data"` is an array now).

{
      "data": [{
        "type": "articles",
        "id": "30cd428f-1a3b-459b-a9a8-0ca87c14dd31",
        "attributes": {
          "title": "JSON API paints my bikeshed!"
        }
      }]
    }

We can get a `List<Article>` from it:

var articles = JsonApi.ResourceFromDocument<List<Article>>(json);
    Assert.AreEqual("JSON API paints my bikeshed!", articles[0].Title);

Mixed Resource Types
---
If your document's collection has heterogenous resource types, you must ensure that the container given to `ResourceFromDocument<T>` can store them or else you will get exceptions at run-time.

For example, consider the following document:

{
      "data": [{
        "type": "articles",
        "id": "30cd428f-1a3b-459b-a9a8-0ca87c14dd31",
        "attributes": {
          "title": "JSON API paints my bikeshed!"
        }
      },{
        "type": "books",
        "id": "4062e824-544c-41c9-9ef0-f05d03476d1e",
        "attributes": {
          "title": "and I wrote a book about it..."
        }
      },{
        "type": "magazines",
        "id": "85b03dc1-8f43-4660-809d-b3869ca0935a",
        "attributes": {
          "title": "which was featured in a magazine!"
        }
      }]
    }

Let's say we wrote a common interface `ITitled`:

public interface ITitled {
        string Title { get; set; }
    }

And classes to hold the `Article`, `Book` and `Magazine` types, all of which implement `ITitled`

public class Article : ITitled {
        public Guid Id { get; set; }
        public string Title { get; set; }
    }

public class Book : ITitled {
        public string Title { get; set; }
    }

public class Magazine : ITitled {
        public string Title { get; set; }
    }

Then we can parse this into a `List<ITitled>`:

var titled = JsonApi.ResourceFromDocument<List<ITitled>>(json);
    Assert.AreEqual("JSON API paints my bikeshed!", titled[0].Title);
    Assert.AreEqual("and I wrote a book about it...", titled[1].Title);
    Assert.AreEqual("which was featured in a magazine!", titled[2].Title);

> If you forgot to make `Article` implement `ITitled`, you would see an exception like this:
>
>     System.ArgumentException: The value "JsonApiNet.Tests.Readme.MixedResources.Article" is
>     not of type "JsonApiNet.Tests.Readme.MixedResources.ITitled" and cannot be used in this
>     generic collection.

Compound Documents
---
Here is a compound document with a collection of resources that have relationships to included data, meta data, links, and more. This is a list of articles. Each article has a relationship to an author and a list of comments.

{
      "data": [{
        "type": "articles",
        "id": "30cd428f-1a3b-459b-a9a8-0ca87c14dd31",
        "attributes": {
          "title": "JSON API paints my bikeshed!"
        },
        "links": {
          "self": "http://example.com/articles/1"
        },
        "relationships": {
          "author": {
            "links": {
              "self": "http://example.com/articles/1/relationships/author",
              "related": "http://example.com/articles/1/author"
            },
            "data": { "type": "people", "id": "9" }
          },
          "comments": {
            "links": {
              "self": "http://example.com/articles/1/relationships/comments",
              "related": "http://example.com/articles/1/comments"
            },
            "data": [
              { "type": "comments", "id": "5" },
              { "type": "comments", "id": "12" }
            ]
          }
        }
      }],
      "included": [{
        "type": "people",
        "id": "9",
        "attributes": {
          "first-name": "Dan",
          "last-name": "Gebhardt",
          "twitter": "dgeb"
        },
        "links": {
          "self": "http://example.com/people/9"
        }
      }, {
        "type": "comments",
        "id": "5",
        "attributes": {
          "body": "First!"
        },
        "links": {
          "self": "http://example.com/comments/5"
        }
      }, {
        "type": "comments",
        "id": "12",
        "attributes": {
          "body": "I like XML better"
        },
        "links": {
          "self": "http://example.com/comments/12"
        }
      }]
    }

We already have an `Article` class from before, but let's extend it with some additional properties:

public class Article {
        public string Title { get; set; }
        public Person Author { get; set; }
        public List<Comment> Comments { get; set; }
    }

A `Person` class for the author:

public class Person {
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }

And a `Comment` class for the comments:

public class Comment {
        public string Body { get; set; }
    }

Nothing changes in how we retrieve the `List<Article>`:

var articles = JsonApi.ResourceFromDocument<List<Article>>(json);
    Assert.AreEqual("JSON API paints my bikeshed!", articles[0].Title);

The author and comments are available too!

var author = articles[0].Author;
    Assert.AreEqual("Gebhardt", author.LastName);

var comments = articles[0].Comments;
    Assert.AreEqual("I like XML better", comments[1].Body);

Property Resolution for Attributes
---
In the examples, you might have noticed that there is a case mismatch between the `"title"` attribute named in the document and the `Title` property on the `Article` class.

The `JsonApiPropertyResolver` is what's responsible for finding the correct property on your `Type`.

> The default resolution process is:
>
> 1. First look in the `Type` for properties with the `[JsonApiAttribute("name")]` attribute, where `"name"` matches the the key from the `"attributes"` object in the document. If a property is found, use that.
>
> 2. Next, look in the `Type` for a name that matches a normalized version of the key from the `"attributes"` object in the document. The normalization applies `Underscore()` and `PascalCase()` to the key, e.g. `"first-name"` becomes `FirstName`.

For example, we could map the `"title"` attribute into a property named `Subject`:

public class Article {
        [JsonApiAttribute("title")]
        public string Subject { get; set; }
    }

Then fetch it back out:

var article = JsonApi.ResourceFromDocument<Article>(json);
    Assert.AreEqual("JSON API paints my bikeshed!", article.Subject);

Customizing Property Resolution
---
If you have complex rules, or you can't annotate your mapped classes, then you will need to write a custom `IJsonApiPropertyResolver` and give it to the serializer when converting your document.

For example, here is an `Article` with a property named `ThingYouCallit`

public class Article {
        public string ThingYouCallIt { get; set; }
    }

We'll write a custom `NamingThingsIsHardResolver` that can map the `title` attribute from our JSON API document into the `ThingYouCallIt` property:

public class NamingThingsIsHardResolver : JsonApiPropertyResolver {
        public override PropertyInfo ResolveJsonApiAttribute(Type type, string attributeName) {
            if (type == typeof(Article) && attributeName == "title") {
                return type.GetProperty("ThingYouCallIt");
            }

return base.ResolveJsonApiAttribute(type, attributeName);
        }
    }

You can use it like this:

var article = JsonApi.ResourceFromDocument<Article>(
        json,
        null,
        new NamingThingsIsHardResolver());

Assert.AreEqual("JSON API paints my bikeshed!", article.ThingYouCallIt);

> Note: Returning `null` for the `ResolveFoo` calls will skip assignment of that property.

Type Resolution for Attributes
---
When parsing the values of an `"attributes"` object, `JsonApiNet` will attempt to deserialize each value into the `Type` associated with the property that the `JsonApiPropertyResolver` chose.

For example, if we have the following document:

{
      "data": {
        "type": "ghost_busters",
        "id": "Egon Spengler",
        "attributes": {
          "quotes": [
            "I collect spores, molds, and fungus."
          ],
        }
      }
    }

We can map it into a `GhostBuster` class like this:

public class GhostBuster {
       public string Id { get; set; }
       public List<string> Quotes { get; set; }
    }

In this example, the `JsonApiPropertyResolver` will resolve the `"quotes"` attribute into the `Quotes` property and then proceed to deserialize the quotes into a `List<string>`.

var ghostBuster = JsonApi.ResourceFromDocument<GhostBuster>(json);
    Assert.AreEqual("I collect spores, molds, and fungus.", ghostBuster.Quotes[0]);

> Note: This is using `Json.NET` under the hood, so you can map complex objects from your `"attributes"` values using `[JsonProperty]`, specify a custom `JsonConverter` on them, etc.!

Property Resolution for Relationships
---
This works exactly the same as Attribute resolution, only you need to use the `[JsonApiRelationship("name")]` attribute instead of `[JsonApiAttribute("name"}]` to map them.

For example, let's say we want to map the `"author"` relationship into a property named `WrittenBy`:

public class Article
    {
        [JsonApiRelationship("author")]
        public Person WrittenBy { get; set; }
    }

And then we can use it like this:

var articles = JsonApi.ResourceFromDocument<List<Article>>(json);
    Assert.AreEqual("Gebhardt", articles[0].WrittenBy.LastName);

Type Resolution for Relationships
---
This **does not** work the same way as attribute types. Resource types are resolved using the `JsonApiTypeResolver`, therefore, you must ensure that the `Type` of the property that your relationships resolve to can hold an instance of the `Type` resolved by the `JsonApiTypeResolver` for the relationship's resource.

Using the _Compound Document_ example from above, this **will not work**:

public class Article {
        [JsonApiRelationship("author")]
        public Comment Author { get; set; }
    }

This doesn't work because the `"type"` for the `"author"` relationship is `"people"`, and the `JsonApiTypeResolver` will resolve this to the `Person` class. The new `Person` instance will then be assigned to the `Author` property (which in this example we've incorrectly specified is a `Comment`), resulting in a run-time exception.

> You'll get an exception like:
>
>     System.ArgumentException: Object of type
>     'JsonApiNet.Tests.Readme.RelationshipPropertyResolution.Person'
>     cannot be converted to type
>     'JsonApiNet.Tests.Readme.RelationshipPropertyResolution.Comment'

Property Resolution for Id and Type
---
If you want to map the `"id"` and `"type"` fields of the resource into your class, you can use the `[JsonApiId]` or `[JsonApiType]` attributes respectively:

public class Article {
        [JsonApiId]
        public Guid Identifier { get; set; }

[JsonApiType]
        public string ResourceType { get; set; }
    }

For the `"id"` field, `JsonApiNet` supports any `Type` that implements a static `Parse(string)` method and will use it to coerce the value found in the document to the appropriate type.

Type Resolution for Resources
---
How does `JsonApiNet` know which class to instantiate for a given resource `"type"`? Enter the `JsonApiTypeResolver`.

When you call `ResourceFromDocument<T>`, you get back an instance of type `T`, but that doesn't mean `JsonApiNet` is instantiating an object of type `T` for your resource types. The type T is a reference point that identifies the default assembly within which the `JsonApiTypeResolver` will search for types.

The `JsonApiTypeResolver` is responsible for determining the correct class to instantiate based on the `"type"` attribute associated with the resource in the JSON API document.

The default `JsonApiTypeResolver` is the `ReflectingTypeResolver` and it works by interrogating all of the `Types` defined in the assembly that defines type `T` looking for classes with the `[JsonApiResourceType("name")]` attribute set.

If a `Type` with a `[JsonApiResourceType("name")]` attribute is found, where `"name"` matches the `typeName` then that type is used.

Otherwise, the first `Type` whose name matches the normalized form of the `typeName` is used. The normalization applies `Underscore()`, `Singularize()`, and `PascalCase()` to the `"type"`, e.g. `"crazy-cats"` becomes `CrazyCat`.

In cases where the definition of types in your object graph includes types defined in other assemblies, it is possible to pass in an array of assemblies to include in type resolution; for example:

Assembly[] additionalAssemblies = {
        typeof(Illustration).GetTypeInfo().Assembly
    };

var doc = JsonApi.ResourceFromDocument<Brochure>(
                json,
                additionalAssemblies: additionalAssemblies);

It turns out this is pretty useful for most common cases; however, if you want to explicitly specify the `Type` chosen for a given resource `"type"` in your document, then you can implement _Custom Type Resolution_ as described below.

> Note: If the `JsonApiTypeResolver` can't find a resource type for any reason, it will throw a `JsonApiTypeNotFoundException`

Custom Type Resolution
---
If for some reason you can't apply the `[JsonApiResourceType]` attribute to your classes, you can also write a custom `IJsonApiTypeResolver` that implements whatever mapping you deem fit:

public class BarneyTypeResolver : IJsonApiTypeResolver {
      public Type ResolveType(string typeName) {
        if (typeName == "rain_drops") {
          return typeof(LemonDrop);
        }

return null;
      }
    }

Then you can use it like so:

var lemonDrop = JsonApi.ResourceFromDocument<LemonDrop>(json, new BarneyTypeResolver())

This particular use-case is so common, that `JsonApiNet` provides a `StringToTypeResolver` which you can initialize with a `Dictionary<string,Type>` where the keys are the `"type"` members in your document and the values are the corresponding `Type` to instantiate:

var resolver = new StringToTypeResolver(
        new Dictionary<string,Type> {
            { "rain_drops", typeof(LemonDrop) }
        }
    );

var lemonDrop = JsonApi.ResourceFromDocument<LemonDrop>(json, resolver);

JsonApiDocument
---
In addition to providing lots of awesome ways to get concrete resource classes out of your JSON API documents, `JsonApiNet` can also get you an object graph that represents the entire JSON API document.

var document = JsonApi.Document(json);

This is an instance of `JsonApiDocument` and has all the good stuff like `Meta`, `Links`, `Errors`, etc parsed into it. For example, if there were `'links'` at the top-level of a document:

{
      "links": {
        "admin": "http://admin.to/articles"
      },
      "data": { ... }
    }

For example, we could fetch the `"admin"` link from the top-level document:

var links = document.Links;
    var adminUrl = links["admin"].Uri;

In this case, `links` would be a `JsonApiLinks` container instance, holding `JsonApiLink` members.

> Note: Each `JsonApiLink` stored in the `JsonApiLinks` container has `Href` and `Meta` properties for fetching the values parsed out of the document and an additional `Uri` helper that converts the `Href` value into a `System.Uri`. In the case of a "simple link" (i.e., a string containing the link's URL), the `Meta` property will be null.

You can get the parsed representation of the resource (a `JsonApiResource` instance) by calling `document.Data`. This instance will let you fetch the `Attributes`, `Relationships`, `Links`, `Id`, `Type`, and `Meta` that were parsed from the document.

All of the properties are named consistently with the specification, so it shouldn't be too hard to discover what you need to drill down to a specific part of the document.

There is a generic from of `Document<T>` that returns a `JsonApiDocument` instance which you can use to access the `Resource` property and get what you would have normally received calling `ResourceFromDocument<T>`.

For example:

var document = JsonApi.Document<Article>(json);
    var article = document.Resource;
    Assert.AreEqual("JSON API paints my bikeshed!", article.Title);

Errors
---
If you are calling `ResourceFromDocument<T>` then the presence of a top-level `"errors"` field will cause `JsonApiNet` to throw a `JsonApiErrorsException` and stop processing the document. You can get the parsed `JsonApiErrors` instance from the `JsonApiErrors` property on the exception.

Otherwise, a top-level `"errors"` field will be parsed into the `Errors` property of the `JsonApiDocument` and it would be up to you to check for the presence of these in your parsed document and handle them appropriately. There is a convenience property named `HasErrors` on the top level document for this purpose.

For example, consider the following response with errors:

{
      "errors": [{
        "id": "8c0f0cef-7141-4da4-ad4a-8bbfff2a81a6",
        "status": 500,
        "title": "Error Title",
        "detail": "Error details go here.",
        "meta": {
          "timestamp": "2015-07-23T07:04:32.987Z",
          "path": "/foo/b",
          "trace": [
            "pf_common_api (2.0.4) lib/pf_common_api/errors/helpers.rb:22:in `render_error'",
            "lib/compressed_requests_middleware.rb:23:in `call'"
          ]
        }
      }]
    }

If you were calling `ResourceFromDocument<T>` you might handle the error like this:

Article article;
    try {
        article = JsonApi.ResourceFromDocument<Article>(json);
    } catch (JsonApiErrorsException e) {
        Console.Error.WriteLine("Wat?! {0}", e.JsonApiErrors.Message);
        throw;
    }

Alternatively, if you were using `DeserializeDocument`, you might handle it like this:

var document = JsonApi.DeserializeDocument<Article>(json);

if (document.HasErrors) {
        Console.Error.WriteLine("Wat?! {0}", document.Errors.Message);
        return;
    }

Either of these would give you an output like:

Wat?! PF::Common::API::Errors::RoutingError: Invalid route

Errata
---

### Deserializing into a Type only known at run-time ###
If you want to deserialize into a container `Type` that is only known at run-time, you can use the non-generic form of `ResourceFromDocument` or `Document` and pass the `ResultType` to the `SerializerSettings`

var article = JsonApi.ResourceFromDocument(
        json,
        new SerializerSettings {
            CreateResource = true,
            ResultType = typeof(Article)
        }
    );

Assert.AreEqual("JSON API paints my bikeshed!", ((Article)article).Title);

### Dependency Injection ###
The static methods provided on `JsonApiNet` are convenience methods. You can also instantiate a `JsonApiNetSerializer` yourself and call the similarly-named methods on it. For example:

var serializer = new JsonApiNetSerializer();
    var article = serializer.ResourceFromDocument<Article>(json);
    Assert.AreEqual("JSON API paints my bikeshed!", article.Title);

The `JsonApinetSerializer` inherits from `IJsonApiNetSerializer` which can inject or mock as you see fit.

Contributing
---
Please fork and submit pull requests. If you aren't sure how to approach a fix, or you want some advice, please feel free to open an issue. No contribution is too small.

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