# jsonapi [![Build Status](https://travis-ci.org/google/jsonapi.svg?branch=master)](https://travis-ci.org/google/jsonapi) [![GoDoc](https://godoc.org/github.com/google/jsonapi?status.svg)](http://godoc.org/github.com/google/jsonapi) A serializer/deserializer for JSON payloads that comply to the [JSON API - jsonapi.org](http://jsonapi.org) spec in go. ## Installation ``` go get -u github.com/google/jsonapi ``` Or, see [Alternative Installation](#alternative-installation). ## Background You are working in your Go web application and you have a struct that is organized similarly to your database schema. You need to send and receive json payloads that adhere to the JSON API spec. Once you realize that your json needed to take on this special form, you go down the path of creating more structs to be able to serialize and deserialize JSON API payloads. Then there are more models required with this additional structure. Ugh! With JSON API, you can keep your model structs as is and use [StructTags](http://golang.org/pkg/reflect/#StructTag) to indicate to JSON API how you want your response built or your request deserialized. What about your relationships? JSON API supports relationships out of the box and will even put them in your response into an `included` side-loaded slice--that contains associated records. ## Introduction JSON API uses [StructField](http://golang.org/pkg/reflect/#StructField) tags to annotate the structs fields that you already have and use in your app and then reads and writes [JSON API](http://jsonapi.org) output based on the instructions you give the library in your JSON API tags. Let's take an example. In your app, you most likely have structs that look similar to these: ```go type Blog struct { ID int `json:"id"` Title string `json:"title"` Posts []*Post `json:"posts"` CurrentPost *Post `json:"current_post"` CurrentPostId int `json:"current_post_id"` CreatedAt time.Time `json:"created_at"` ViewCount int `json:"view_count"` } type Post struct { ID int `json:"id"` BlogID int `json:"blog_id"` Title string `json:"title"` Body string `json:"body"` Comments []*Comment `json:"comments"` } type Comment struct { Id int `json:"id"` PostID int `json:"post_id"` Body string `json:"body"` Likes uint `json:"likes_count,omitempty"` } ``` These structs may or may not resemble the layout of your database. But these are the ones that you want to use right? You wouldn't want to use structs like those that JSON API sends because it is difficult to get at all of your data easily. ## Example App [examples/app.go](https://github.com/google/jsonapi/blob/master/examples/app.go) This runnable file demonstrates the implementation of a create, a show, and a list [http.Handler](http://golang.org/pkg/net/http#Handler). It outputs some example requests and responses as well as serialized examples of the source/target structs to json. That is to say, I show you that the library has successfully taken your JSON API request and turned it into your struct types. To run, * Make sure you have go installed * Create the following directories or similar: `~/go` * Set `GOPATH` to `PWD` in your shell session, `export GOPATH=$PWD` * `go get github.com/google/jsonapi`. (Append `-u` after `get` if you are updating.) * `go run $GOPATH/src/github.com/google/jsonapi/examples/app.go` or `cd $GOPATH/src/github.com/google/jsonapi/examples && go run app.go` ## `jsonapi` Tag Reference ### Example The `jsonapi` [StructTags](http://golang.org/pkg/reflect/#StructTag) tells this library how to marshal and unmarshal your structs into JSON API payloads and your JSON API payloads to structs, respectively. Then Use JSON API's Marshal and Unmarshal methods to construct and read your responses and replies. Here's an example of the structs above using JSON API tags: ```go type Blog struct { ID int `jsonapi:"primary,blogs"` Title string `jsonapi:"attr,title"` Posts []*Post `jsonapi:"relation,posts"` CurrentPost *Post `jsonapi:"relation,current_post"` CurrentPostID int `jsonapi:"attr,current_post_id"` CreatedAt time.Time `jsonapi:"attr,created_at"` ViewCount int `jsonapi:"attr,view_count"` } type Post struct { ID int `jsonapi:"primary,posts"` BlogID int `jsonapi:"attr,blog_id"` Title string `jsonapi:"attr,title"` Body string `jsonapi:"attr,body"` Comments []*Comment `jsonapi:"relation,comments"` } type Comment struct { ID int `jsonapi:"primary,comments"` PostID int `jsonapi:"attr,post_id"` Body string `jsonapi:"attr,body"` Likes uint `jsonapi:"attr,likes-count,omitempty"` } ``` ### Permitted Tag Values #### `primary` ``` `jsonapi:"primary,"` ``` This indicates this is the primary key field for this struct type. Tag value arguments are comma separated. The first argument must be, `primary`, and the second must be the name that should appear in the `type`\* field for all data objects that represent this type of model. \* According the [JSON API](http://jsonapi.org) spec, the plural record types are shown in the examples, but not required. #### `attr` ``` `jsonapi:"attr,,"` ``` These fields' values will end up in the `attributes`hash for a record. The first argument must be, `attr`, and the second should be the name for the key to display in the `attributes` hash for that record. The optional third argument is `omitempty` - if it is present the field will not be present in the `"attributes"` if the field's value is equivalent to the field types empty value (ie if the `count` field is of type `int`, `omitempty` will omit the field when `count` has a value of `0`). Lastly, the spec indicates that `attributes` key names should be dasherized for multiple word field names. #### `relation` ``` `jsonapi:"relation,,"` ``` Relations are struct fields that represent a one-to-one or one-to-many relationship with other structs. JSON API will traverse the graph of relationships and marshal or unmarshal records. The first argument must be, `relation`, and the second should be the name of the relationship, used as the key in the `relationships` hash for the record. The optional third argument is `omitempty` - if present will prevent non existent to-one and to-many from being serialized. ## Methods Reference **All `Marshal` and `Unmarshal` methods expect pointers to struct instance or slices of the same contained with the `interface{}`s** Now you have your structs prepared to be seralized or materialized, What about the rest? ### Create Record Example You can Unmarshal a JSON API payload using [jsonapi.UnmarshalPayload](http://godoc.org/github.com/google/jsonapi#UnmarshalPayload). It reads from an [io.Reader](https://golang.org/pkg/io/#Reader) containing a JSON API payload for one record (but can have related records). Then, it materializes a struct that you created and passed in (using new or &). Again, the method supports single records only, at the top level, in request payloads at the moment. Bulk creates and updates are not supported yet. After saving your record, you can use, [MarshalOnePayload](http://godoc.org/github.com/google/jsonapi#MarshalOnePayload), to write the JSON API response to an [io.Writer](https://golang.org/pkg/io/#Writer). #### `UnmarshalPayload` ```go UnmarshalPayload(in io.Reader, model interface{}) ``` Visit [godoc](http://godoc.org/github.com/google/jsonapi#UnmarshalPayload) #### `MarshalOnePayload` ```go MarshalOnePayload(w io.Writer, model interface{}) error ``` Visit [godoc](http://godoc.org/github.com/google/jsonapi#MarshalOnePayload) Writes a JSON API response, with related records sideloaded, into an `included` array. This method encodes a response for a single record only. If you want to serialize many records, see, [MarshalManyPayload](#marshalmanypayload). ##### Handler Example Code ```go func CreateBlog(w http.ResponseWriter, r *http.Request) { blog := new(Blog) if err := jsonapi.UnmarshalPayload(r.Body, blog); err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) return } // ...save your blog... w.WriteHeader(http.StatusCreated) w.Header().Set("Content-Type", jsonapi.MediaType) if err := jsonapi.MarshalOnePayload(w, blog); err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) } } ``` ### List Records Example #### `MarshalManyPayload` ```go MarshalManyPayload(w io.Writer, models []interface{}) error ``` Visit [godoc](http://godoc.org/github.com/google/jsonapi#MarshalManyPayload) Takes an `io.Writer` and an slice of `interface{}`. Note, if you have a type safe array of your structs, like, ```go var blogs []*Blog ``` you will need to iterate over the slice of `Blog` pointers and append them to an interface array, like, ```go blogInterface := make([]interface{}, len(blogs)) for i, blog := range blogs { blogInterface[i] = blog } ``` Alternatively, you can insert your `Blog`s into a slice of `interface{}` the first time. For example when you fetch the `Blog`s from the db `append` them to an `[]interface{}` rather than a `[]*Blog`. So your method signature to reach into your data store may look something like this, ```go func FetchBlogs() ([]interface{}, error) ``` ##### Handler Example Code ```go func ListBlogs(w http.ResponseWriter, r *http.Request) { // ...fetch your blogs, filter, offset, limit, etc... // but, for now blogs := testBlogsForList() w.WriteHeader(http.StatusOK) w.Header().Set("Content-Type", jsonapi.MediaType) if err := jsonapi.MarshalManyPayload(w, blogs); err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) } } ``` ### Create Records Example #### `UnmarshalManyPayload` ```go UnmarshalManyPayload(in io.Reader, t reflect.Type) ([]interface{}, error) ``` Visit [godoc](http://godoc.org/github.com/google/jsonapi#UnmarshalManyPayload) Takes an `io.Reader` and a `reflect.Type` representing the uniform type contained within the `"data"` JSON API member. ##### Handler Example Code ```go func CreateBlogs(w http.ResponseWriter, r *http.Request) { // ...create many blogs at once blogs, err := UnmarshalManyPayload(r.Body, reflect.TypeOf(new(Blog))) if err != nil { t.Fatal(err) } for _, blog := range blogs { b, ok := blog.(*Blog) // ...save each of your blogs } w.WriteHeader(http.StatusCreated) w.Header().Set("Content-Type", jsonapi.MediaType) if err := jsonapi.MarshalManyPayload(w, blogs); err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) } } ``` ### Links If you need to include [link objects](http://jsonapi.org/format/#document-links) along with response data, implement the `Linkable` interface for document-links, and `RelationshipLinkable` for relationship links: ```go func (post Post) JSONAPILinks() *Links { return &Links{ "self": "href": fmt.Sprintf("https://example.com/posts/%d", post.ID), "comments": Link{ Href: fmt.Sprintf("https://example.com/api/blogs/%d/comments", post.ID), Meta: map[string]interface{}{ "counts": map[string]uint{ "likes": 4, }, }, }, } } // Invoked for each relationship defined on the Post struct when marshaled func (post Post) JSONAPIRelationshipLinks(relation string) *Links { if relation == "comments" { return &Links{ "related": fmt.Sprintf("https://example.com/posts/%d/comments", post.ID), } } return nil } ``` ### Meta If you need to include [meta objects](http://jsonapi.org/format/#document-meta) along with response data, implement the `Metable` interface for document-meta, and `RelationshipMetable` for relationship meta: ```go func (post Post) JSONAPIMeta() *Meta { return &Meta{ "details": "sample details here", } } // Invoked for each relationship defined on the Post struct when marshaled func (post Post) JSONAPIRelationshipMeta(relation string) *Meta { if relation == "comments" { return &Meta{ "this": map[string]interface{}{ "can": map[string]interface{}{ "go": []interface{}{ "as", "deep", map[string]interface{}{ "as": "required", }, }, }, }, } } return nil } ``` ### Errors This package also implements support for JSON API compatible `errors` payloads using the following types. #### `MarshalErrors` ```go MarshalErrors(w io.Writer, errs []*ErrorObject) error ``` Writes a JSON API response using the given `[]error`. #### `ErrorsPayload` ```go type ErrorsPayload struct { Errors []*ErrorObject `json:"errors"` } ``` ErrorsPayload is a serializer struct for representing a valid JSON API errors payload. #### `ErrorObject` ```go type ErrorObject struct { ... } // Error implements the `Error` interface. func (e *ErrorObject) Error() string { return fmt.Sprintf("Error: %s %s\n", e.Title, e.Detail) } ``` ErrorObject is an `Error` implementation as well as an implementation of the JSON API error object. The main idea behind this struct is that you can use it directly in your code as an error type and pass it directly to `MarshalErrors` to get a valid JSON API errors payload. ##### Errors Example Code ```go // An error has come up in your code, so set an appropriate status, and serialize the error. if err := validate(&myStructToValidate); err != nil { context.SetStatusCode(http.StatusBadRequest) // Or however you need to set a status. jsonapi.MarshalErrors(w, []*ErrorObject{{ Title: "Validation Error", Detail: "Given request body was invalid.", Status: "400", Meta: map[string]interface{}{"field": "some_field", "error": "bad type", "expected": "string", "received": "float64"}, }}) return } ``` ## Testing ### `MarshalOnePayloadEmbedded` ```go MarshalOnePayloadEmbedded(w io.Writer, model interface{}) error ``` Visit [godoc](http://godoc.org/github.com/google/jsonapi#MarshalOnePayloadEmbedded) This method is not strictly meant to for use in implementation code, although feel free. It was mainly created for use in tests; in most cases, your request payloads for create will be embedded rather than sideloaded for related records. This method will serialize a single struct pointer into an embedded json response. In other words, there will be no, `included`, array in the json; all relationships will be serialized inline with the data. However, in tests, you may want to construct payloads to post to create methods that are embedded to most closely model the payloads that will be produced by the client. This method aims to enable that. ### Example ```go out := bytes.NewBuffer(nil) // testModel returns a pointer to a Blog jsonapi.MarshalOnePayloadEmbedded(out, testModel()) h := new(BlogsHandler) w := httptest.NewRecorder() r, _ := http.NewRequest(http.MethodPost, "/blogs", out) h.CreateBlog(w, r) blog := new(Blog) jsonapi.UnmarshalPayload(w.Body, blog) // ... assert stuff about blog here ... ``` ## Alternative Installation I use git subtrees to manage dependencies rather than `go get` so that the src is committed to my repo. ``` git subtree add --squash --prefix=src/github.com/google/jsonapi https://github.com/google/jsonapi.git master ``` To update, ``` git subtree pull --squash --prefix=src/github.com/google/jsonapi https://github.com/google/jsonapi.git master ``` This assumes that I have my repo structured with a `src` dir containing a collection of packages and `GOPATH` is set to the root folder--containing `src`. ## Contributing Fork, Change, Pull Request *with tests*.