gather: add transformKey function

README.md

@@ -168,10 +168,10 @@ function TodoList (sources) {
 And how do we process fetched data?
 ---
 
-It's a quite common use case when a collection is built from fetched data. Usually it comes in a form of items' state snapshot. `Collection.gather` takes a stream of those snapshots and turns into a stream of collections. It takes `Collection` and `sources` arguments, just as `Collection` does, plus `itemState$` and an optional `idAttribute` argument, which defaults to `'id'`.
+It's a quite common use case when a collection is built from fetched data. Usually it comes in a form of items' state snapshot. `Collection.gather` takes a stream of those snapshots and turns into a stream of collections. It takes `Collection` and `sources` arguments, just as `Collection` does, plus the snapshots stream `itemState$`, an optional `idAttribute` argument, which defaults to `'id'`, and an optional `transformKey` function for converting source keys.
 
 ```js
-const tasks$ = Collection.gather(Task, sources, fetchedTasks$, 'uid')
+const tasks$ = Collection.gather(Task, sources, fetchedTasks$, 'uid', key => `${key}$`) // converts 'props' in snapshots to 'props$' in sources
 ```
 
 It uses a set of rules:

examples/taskrunner/app.js

@@ -27,7 +27,7 @@ function taskView ([{status, text}, editing]) {
   );
 }
 
-function Task ({DOM, props}) {
+function Task ({DOM, props$}) {
   const delete$ = DOM
     .select('.delete')
     .events('click');
@@ -47,11 +47,11 @@ function Task ({DOM, props}) {
   const edit$ = editing$.map(editing => changeText$.filter(() => editing)).flatten();
 
   return {
-    DOM: xs.combine(props, editing$).map(taskView),
-    complete$: props.map(({status}) => status === 'complete'),
+    DOM: xs.combine(props$, editing$).map(taskView),
+    complete$: props$.map(({status}) => status === 'complete'),
     delete$,
     edit$,
-    HTTP: props.map(({id}) => ({
+    HTTP: props$.map(({id}) => ({
       url: `/tasks/${id}`
     }))
   };
@@ -131,7 +131,7 @@ export default function TaskRunner ({DOM, HTTP}) {
     )
     .startWith([]);
 
-  const tasks$ = Collection.gather(Task, {DOM}, tasksState$);
+  const tasks$ = Collection.gather(Task, {DOM}, tasksState$, 'id', key => `${key}$`);
 
   const addTaskClick$ = DOM
     .select('.add-task')

src/collection.js

@@ -143,7 +143,7 @@ function makeCollection (externalSA = xsAdapter) {
   };
 
   // convert a stream of items' sources snapshots into a stream of collections
-  Collection.gather = function gather (component, sources, sourceItems$, idAttribute = 'id') {
+  Collection.gather = function gather (component, sources, sourceItems$, idAttribute = 'id', transformKey = null) {
     function makeDestroyable (component) {
       return (sources) => ({
         ...component(sources),
@@ -196,9 +196,11 @@ function makeCollection (externalSA = xsAdapter) {
             .compose(dropRepeats(compareJSON))
             .remember();
 
+          const sourceKey = transformKey ? transformKey(key) : key;
+
           return {
             ...sources,
-            [key]: convert(stream$, xsAdapter, externalSA)
+            [sourceKey]: convert(stream$, xsAdapter, externalSA)
           };
         }, {
           _destroy$

test/gather-diversity-test.js

@@ -186,4 +186,22 @@ describe('Collection.gather with different stream libs', () => {
       }
     });
   });
+
+  it('uses transformKey function to transform source keys', (done) => {
+    const itemState$ = O.of([
+      {id: 0, props: {foo: 'bar'}}
+    ]);
+
+    function MockedComponent (sources) {
+      assert.ok(sources.props$);
+      done();
+    }
+
+    const collection$ = Collection.gather(MockedComponent, {}, itemState$, 'id', key => `${key}$`);
+    collection$.subscribe({
+      next () {},
+      error (err) { done(err); },
+      complete () {}
+    });
+  });
 });

test/gather-test.js

@@ -183,4 +183,22 @@ describe('Collection.gather', () => {
       }
     });
   });
+
+  it('uses transformKey function to transform source keys', (done) => {
+    const itemState$ = xs.of([
+      {id: 0, props: {foo: 'bar'}}
+    ]);
+
+    function MockedComponent (sources) {
+      assert.ok(sources.props$);
+      done();
+    }
+
+    const collection$ = Collection.gather(MockedComponent, {}, itemState$, 'id', key => `${key}$`);
+    collection$.addListener({
+      next () {},
+      error (err) { done(err); },
+      complete () {}
+    });
+  });
 });