DOJO: Lazy loading nodes in LazyTreeGrid - looking

Question

I'm looking for an example of how to use QueryReadStore (or some other store) with dojox.grid.LazyTreeGrid ?

I want to be able to display big structures and load only necessary required data from server. Only children of open nodes should be loaded from dedicated server script.

I'm already using QueryReadStore with dojox.grid.DataGrid and it works great :)

Help, Thanks.

Answer 1

I think I have what you are looking for here. Some excellent example code on using QueryReadStore with dojox.grid.LazyTreeGrid, and it's fully explained step by step too.

Please see here: http://livedocs.dojotoolkit.org/dojox/grid/LazyTreeGrid

I hope this advances your work and you are able to accomplish your goals.

Regards

Frank.

Answer 2

Here is a long-winded explanation/sample based on some stuff I am currently doing. This assumes basic comfort with Dojo 1.7-style packages (for instance, we assume the default Dojo packages are correctly set-up).

Client-side (js file)

require(["dojo/ready",
    "dojox/grid/LazyTreeGridStoreModel",
    "dojox/data/QueryReadStore",
    "dojox/grid/LazyTreeGrid"], function(ready, LazyTreeGridStoreModel, QueryReadStore, LazyTreeGrid) {
        ready(function() {
            var cellLayout = [
                {name: 'Name of fruit', field: 'name', width: '300px', defaultValue: ""},
                {name: 'Color of fruit', field: 'color', width: '100px', defaultValue: ""},
                {name: 'Size of fruit', field: 'size', width: '100px', defaultValue: ""}
            ];

            // This is the url on which your server will listen for GET requests
            var dataStore = new QueryReadStore({url: "url/to/load/rows"});
            var treeModel = new LazyTreeGridStoreModel({store: dataStore, childrenAttrs: ['children'], serverStore: true});

            var grid = new LazyTreeGrid({
                treeModel: treeModel,
                structure: cellLayout,
                autoHeight: 20}, "gridContainerId"); // you need to have a DOM element by that id
            grid.startup();
        }
    });

Server-side:

You need a server-side handler that will listen to GET requests on url/to/load/rows. Those requests will have up to 3 parameters:

start    - 0-based index of the first item to return
count    - number of items to return
parentId - Id of the parent of the children items that are requested.
           Optional, not present for 1st call (because 1st-level objects have no parents).

That handler can be written in your favorite server-side language (i.e. C# with ASP.Net MVC, Ruby, etc.)

The job of your server handler will be to return a json structure containing the following 3 attributes:

items       - Array containing the items you want to display.
              Each item represents a row in the grid. Each item should
              have at least some of the fields you specified in your layout
              and must have the 2 following characteristics:
                - Must have a "children" attribute. That is a bool value.
                  If true, the row is assumed to have children and will have
                  an expando left of it. The grid query the server for children when you expand it.
                  If false, the row is considered terminal, no expando is shown.

                - Must have a unique id. This will be the id that will be set in the "parentId"
                  param when querying the server for the children of that row. It must be stored
                  in the field referred to by the "identifier" attribute (see below).

identifier  - The name of the attribute of each item that contains its unique id.
numRows     - The number of total items existing on this level (not just the number of items you sent back).
              This is used to set the grid & scrollbar size and other UI things.

Client/Server communication

To build upon my previous example, as soon as the grid is started-up (client-side), it will request something like:

GET url/to/load/rows?start=0&count=25

The server would return the following:

{
    "items":[
        {"name": "apple", "color": "red", "size": "small", "uniqueId":"a1", "children": true},
        {"name": "watermelon", "color": "green", "size": "big", "uniqueId":"b1", "children": false}
    ],
    "identifier": "uniqueId",
    "numRows":2
}

The grid will display the 2 fruits. apple will have an expando, but not watermelon (due to the children attribute). Assume the user clicked on the apple expando. The grid will request its children:

GET url/to/load/rows?parentId=a1&start=0&count=25

The server could return something like:

{
    "items":[
        {"name": "mcintosh", "color": "red-green", "size": "small", "uniqueId":"a2", "children": false}
    ],
    "identifier": "uniqueId",
    "numRows":1
}

The grid will then display a single child under the apple row.