Added isNew and also urlRoot

__tests__/Model.spec.js

@@ -15,13 +15,8 @@ class MyCollection extends Collection {
 }
 
 class MyModel extends Model {
-  url () {
-    const id = this.has('id') && this.get('id')
-    if (id) {
-      return `/resources/${id}`
-    } else {
-      return '/resources'
-    }
+  urlRoot () {
+    return '/resources'
   }
 }
 
@@ -46,16 +41,46 @@ describe('Model', () => {
     model = collection.at(0)
   })
 
+  describe('isNew', () => {
+    it('returns true if it does not have an id', () => {
+      const newModel = new MyModel({})
+      expect(newModel.isNew).toBe(true)
+    })
+
+    it('returns false if it does not have an id', () => {
+      const newModel = new MyModel({ id: 4 })
+      expect(newModel.isNew).toBe(false)
+    })
+  })
+
   describe('url', () => {
-    it('returns the collection one', () => {
-      expect(model.url()).toBe('/resources/1')
+    describe('when the model has a collection', () => {
+      it('returns the collection one', () => {
+        expect(model.url()).toBe('/resources/1')
+      })
     })
 
-    it('throws if the model does not have a collection', () => {
-      expect(() => {
-        const newModel = new Model({ id: 1 })
-        newModel.url()
-      }).toThrowError()
+    describe('when the model has no collection', () => {
+      describe('and no urlRoot', () => {
+        it('throws', () => {
+          expect(() => {
+            const newModel = new Model({ id: 1 })
+            newModel.url()
+          }).toThrowError()
+        })
+      })
+
+      describe('and urlRoot is defined', () => {
+        it('returns different urls depending whether is new or not', () => {
+          let newModel
+
+          newModel = new MyModel({})
+          expect(newModel.url()).toBe('/resources')
+
+          newModel = new MyModel({ id: 3 })
+          expect(newModel.url()).toBe('/resources/3')
+        })
+      })
     })
   })
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "mobx-rest",
-  "version": "1.0.2",
+  "version": "1.0.3",
   "description": "REST conventions for mobx.",
   "repository": {
     "type": "git",

src/Model.js

@@ -1,5 +1,14 @@
 // @flow
-import { observable, asMap, asFlat, action, asReference, ObservableMap, runInAction } from 'mobx'
+import {
+  observable,
+  asMap,
+  asFlat,
+  action,
+  asReference,
+  ObservableMap,
+  computed,
+  runInAction
+} from 'mobx'
 import Collection from './Collection'
 import { uniqueId, isString, debounce } from 'lodash'
 import apiClient from './apiClient'
@@ -27,16 +36,47 @@ export default class Model {
   }
 
   /**
-   * Return the url for this given REST resource
+   * Return the base url used in
+   * the `url` method
    *
    * @abstract
    */
+  urlRoot () {
+    throw new Error('`url` method not implemented')
+  }
+
+  /**
+   * Return the url for this given REST resource
+   */
   url (): string {
+    let urlRoot
+
     if (this.collection) {
-      return `${this.collection.url()}/${this.get('id')}`
+      urlRoot = this.collection.url()
+    } else {
+      urlRoot = this.urlRoot()
     }
 
-    throw new Error('`url` method not implemented')
+    if (!urlRoot) {
+      throw new Error('Either implement `urlRoot` or assign a collection')
+    }
+
+    if (this.isNew) {
+      return urlRoot
+    } else {
+      return `${urlRoot}/${this.get('id')}`
+    }
+  }
+
+  /**
+   * Wether the resource is new or not
+   *
+   * We determine this asking if it contains
+   * the `id` attribute (set by the server).
+   */
+  @computed
+  get isNew (): boolean {
+    return !this.has('id')
   }
 
   /**