Initial path templates proposal

active/0000-path-templates.md

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+- Start Date: 2014-08-20
+- RFC PR:
+- Ember Issue:
+
+## Summary
+
+`pathTemplate` improves the extesibility of API endpoint urls in `RESTAdapter`.
+
+## Motivation
+
+I think that Ember Data has a reputation for being hard to configure. I've often
+heard it recommended to design the server API around what Ember Data expects.
+Considering a lot of thought has gone in to the default RESTAdapter API, this
+is sound advice. However, this is a false and damaging reputation. The adapter
+and serializer pattern that Ember Data uses makes it incredibly extensible. The
+barrier of entry is high though, and it's not obvious how to get the url you need
+unless it's [a namespace](http://emberjs.com/guides/models/connecting-to-an-http-server/#toc_url-prefix)
+or something [pathForType](http://emberjs.com/guides/models/customizing-adapters/#toc_path-customization)
+can handle. Otherwise it's "override `buildURL`". `RESTSerializer` was recently
+improved to make handling various JSON structures easier; it's time for url
+configuration to be easy too.
+
+## Detailed Design
+
+`buildURL` and associated methods and properties will be moved to a mixin design
+to handle url generation only. `buildURL` will use templates to generate a URL
+instead of manually assembling parts. Simple usage example:
+
+```javascript
+export default DS.RESTAdapter.extend({
+  namespace: 'api/v1',
+  pathTemplate: '/:namespace/posts/:id'
+});
+```
+
+### Resolving template segments
+
+Each dynamic path segment will be resolved on a singleton object based on a `pathSegments`
+object provided in the adapter. This `pathSegments` object will feel similar to defining
+actions on routes and controllers.
+
+```javascript
+// adapter
+export default DS.RESTAdapter.extend({
+  namespace: 'api/v1',
+  pathTemplate: '/:namespace/posts/:post_id/:category_name/:id',
+
+  pathSegments: {
+    category_name: function(record) {
+      return _pathForCategory(record.get('category'));
+    }
+
+    post_id: function(record) {
+      return record.get('post.id');
+    };
+  }
+});
+```
+
+#### Psuedo implementation
+
+```javascript
+RESTAdapter = Adapter.extend({
+  buildURL: function(type, id, record) {
+    var urlResolver = _lookupURLResolver(type);
+    var template = this.get('urlTemplate')
+    var urlParts = _parseURLTemplate(template, function(name) {
+      var fn = urlResolver.get(name);
+      return fn(record);
+    });
+
+    return this.urlPrefix(urlParts.compact().join('/'));
+  }
+});
+
+function _lookupURLResolver(type) {
+  // a singleton object will be created using pathSegments that includes important
+  // adapter attributes (such as namespace and host) and delegates unknown
+  // properties to the record, with something like:
+  //
+  //  unknownProperty: function(key) {
+  //    return function(record) { return record.get(key); };
+  //  }
+};
+
+// This is the simplest
+function _parseURLTemplate(template, fn) {
+  var parts = template.split('/');
+  return parts.map(function(part) {
+    if (_isDynamicSegment(part)) { // if segment starts with a `:`
+      return fn(_segmentName(part)); // strip off the `:`
+    } else {
+      return part;
+    }
+  });
+};
+```
+
+### Different URL templates per action
+
+Configuring different urls for different actions becomes fairly trivial with this
+system in place:
+
+#### Usage
+
+```javascript
+// adapter
+export default DS.RESTAdapter.extend({
+  namespace: 'api/v1',
+  pathTemplate: '/:namespace/posts/:post_id/:id',
+  createPathTemplate: '/:namespace/comments',
+  hasManyTemplate: '/:namespace/posts/:post_id/comments',
+
+  pathSegments: {
+    post_id: function(record) {
+      return record.get('post.id');
+    };
+  }
+});
+```
+
+#### Psuedo implementation
+
+```javascript
+RESTAdapter = Adapter.extend({
+  createRecord: function(store, type, payload) {
+    // ...
+    var url = this.buildURL(type.typeKey, null, record, 'create');
+    return this.ajax(url, "POST", { data: data });
+  },
+
+  buildURL: function(type, id, record, action) {
+    var template = this.get(action + 'UrlTemplate') || this.get('urlTemplate);
+    // ...
+  }
+});
+```
+
+## Drawbacks
+
+* Building URLs in this way is likely to be less performant. If this proposal is
+  generally accepted, I will run benchmarks.
+
+## Alternatives
+
+The main alternative that comes to mind, that would make it easier to configure
+urls in the adapter, would be to generally simplify `buildURL` and create more
+hooks.
+
+## Unresolved Questions
+
+* How many templates are reasonable? There could be templates for different
+  operations such as `createRecord`, `updateRecord`, but also `findQuery`, etc.
+* How do we handle generating urls for actions that do not have a single
+  record? This includes `findAll` and `findQuery`, which have no record, and
+  `findMany` and `findHasMany` which have a collection of records.
+