Allow resources to specify meta using the new MarshalMeta interface (#320)

- Changed the Meta field to use json.RawMessage type to match which Attributes
- Added Basic test for New GetMeta Interface

Author: L-four

jsonapi/data_structs.go

@@ -120,6 +120,7 @@ type Data struct {
 	Attributes    json.RawMessage         `json:"attributes"`
 	Relationships map[string]Relationship `json:"relationships,omitempty"`
 	Links         Links                   `json:"links,omitempty"`
+	Meta          json.RawMessage         `json:"meta,omitempty"`
 }
 
 // Relationship contains reference IDs to the related structs

jsonapi/fixtures_test.go

@@ -500,6 +500,24 @@ func (n CustomLinksPost) GetCustomLinks(base string) Links {
 	}
 }
 
+type CustomResourceMetaPost struct{}
+
+func (n CustomResourceMetaPost) GetID() string {
+	return "someID"
+}
+
+func (n *CustomResourceMetaPost) SetID(ID string) error {
+	return nil
+}
+
+func (n CustomResourceMetaPost) GetName() string {
+	return "posts"
+}
+
+func (n CustomResourceMetaPost) Meta() Meta {
+	return Meta{"access_count": 15}
+}
+
 type CustomMetaPost struct{}
 
 func (n CustomMetaPost) GetID() string {

jsonapi/marshal.go

@@ -80,6 +80,13 @@ type MarshalCustomLinks interface {
 	GetCustomLinks(string) Links
 }
 
+// The MarshalMeta interface can be implemented if the struct should
+// want any meta.
+type MarshalMeta interface {
+	MarshalIdentifier
+	Meta() Meta
+}
+
 // The MarshalCustomRelationshipMeta interface can be implemented if the struct should
 // want a custom meta in a relationship.
 type MarshalCustomRelationshipMeta interface {
@@ -254,6 +261,14 @@ func marshalData(element MarshalIdentifier, data *Data, information ServerInform
 		}
 	}
 
+	if casteMetaTarget, ok := element.(MarshalMeta); ok {
+		meta := casteMetaTarget.Meta()
+		data.Meta, err = json.Marshal(meta)
+		if err != nil {
+			return err
+		}
+	}
+
 	if references, ok := element.(MarshalLinkedRelations); ok {
 		data.Relationships = getStructRelationships(references, information)
 	}

jsonapi/marshal_test.go

@@ -271,6 +271,22 @@ var _ = Describe("Marshalling", func() {
 		})
 	})
 
+	Context("When marshaling objects with data meta", func() {
+		It("contains the meta in the marshaled data object", func() {
+			post := CustomResourceMetaPost{}
+			i, err := Marshal(post)
+			Expect(err).To(BeNil())
+			Expect(i).To(MatchJSON(`{
+				"data": {
+					"type": "posts",
+					"id": "someID",
+					"attributes": {},
+					"meta": { "access_count": 15 }
+				}
+			}`))
+		})
+	})
+
 	Context("When marshaling compound objects", func() {
 		It("marshals nested objects", func() {
 			comment1 := Comment{ID: 1, Text: "First!", SubCommentsEmpty: true}