Dojo, JsonRestStore and transaction referencing

Last weeks I need to work with a tree structure. Since I'm using Zend Framework, I decided to use the Dojo Toolkit to make it.

After a review of the consistent dojo.data.api, I was very impressed because it allow you to reuse your widget with different data stores (XML, JSON, etc.).

I decide to use the Zend_Rest component developed by Luke Crouch at the server side to make a RESTful web service, and dojox.data.JsonRestStore at the client side to communicate with this service.

The setup of the tree widget is trivial following the dojo documentation:

var store = new dojox.data.JsonRestStore({target: "http://example.org/restfulservice");
var model = new dijit.tree.TreeStoreModel({store: store, query:{id:"one"}});
var tree = new dijit.Tree({model: model}, "treeDivId");

How the JsonRestStore works.

The JsonRestStore object support transactions, so you can create and modify several nodes and then call the tree.save() method which fires two request for each dirty node:

1. A POST request to example.org/restfulservice to create the new node.
2. A PUT request to example.org/restfultservice/parentId to update the children attribute at the parent node.

The widget works like a charm, but I found a problem when I try to add a child to a recently created node.

An example.

Suppose we have a tree like this (id:label):

1:root
  6:one
    12:one.one
    15:one.two
      23:one.two.one
  9:two

You add a child to 12:one.one but you does not call the tree.save() method. Dojo assigns internally an auto-generated identifier to this node and the tree looks like this:

1:root
  6:one
    12:one.one
      fooID:one.one.one
    15:one.two
      23:one.two.one
  9:two

Now you add a child to this node:

1:root
  6:one
    12:one.one
       fooID:one.one.one
         barID:one.one.one.one
    15:one.two
       23:one.two.one
  9:two

Finally, you call tree.save() method and these requests are fired:

1. A POST request to http://example.org/restfulservice to save one.one.one (Suppose the server creates it with 25 as identifier)
2. A PUT request to http://example.org/restfulservice/12 to update one.one children
3. A POST request to http://example.org/restfulservice to save one.one.one.one
4. A PUT request to http://example.org/restfulservice/fooID to update one.one.one children

The problem.

The problem is that when the fourth request is sent to the server, the node has not been updated by the result of the first one, so it does not have the identifier assigned by the server (25), but the assigned by dojo at the client side (fooID) which is not going to be recognized by the server, so how can the server know which node to update?

The solution.

Well, the solution is very simple and you can find it at the sitepen blog:

JsonRestStore 1.3 solves this problem borrowing a referencing technique from RFC 2387 (multipart/related). When new items are created, the POST request will include a Content-ID header indicating a temporary id for the item. Other items being committed in the same transaction can then refer to the item by the cid: protocol with JSON referencing.

The server should save a temporary array which matches the temporary identifier assigned by dojo with the server one, so when a PUT request is sent to update a node, the server should look at this array for the client identifier and locate the real identifier of the node supposed to be updated.

I've checked that these requests are sent in synchronous mode, so the PUT request for a node is never sent before the POST request that creates it.

Simple, don't you think?

Any typo or problem? Edit this page on Github

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