Create an app to access a public OData source, Working with SharePoint 2013 REST service

http://msdn.microsoft.com/en-us/library/office/fp142380.aspx
vs2012->file->new->project c# ->office/sharepoint->apps->apps for sharepoint 2013-> "AppLevelECTB2"

AppLevelECTB2 -> right click -> add -> select "content types for external data source"

-> http://services.odata.org/Northwind/Northwind.svc

-> ODataWebNorthwindModel

click on "next" -> select "Customers" table [make sure select below check box] -> click on "finish"

go to AppLevelECTB2 -> Pages -> Default.aspx open 

add below div in place of "ContentPlaceHolderID"

  <div id="displayDiv"></div>

go to AppLevelECTB2 -> Scripts -> App.js open

add below javascript

$(document).ready(function () {

    //Namespace

    window.AppLevelECT = window.AppLevelECT || {};

    //Constructor

    AppLevelECT.Grid = function (hostElement, surlWeb) {

        this.hostElement = hostElement;

        if (surlWeb.length > 0 && surlWeb.substring(surlWeb.length - 1, surlWeb.length) != "/")

            surlWeb += "/";

        this.surlWeb = surlWeb;

    }

    //Prototype

    AppLevelECT.Grid.prototype = {

        init: function () {

            $.ajax({

                url: this.surlWeb + "_api/lists/getbytitle('Customers')/items?$select=BdcIdentity,CustomerID,ContactName",

                method: "GET",

                headers: { "Accept": "application/json; odata=verbose" },

                success: this.showItems

            });

        },

        showItems: function (data) {

            var items = [];

            items.push("<table>");

            items.push('<tr><td>Customer ID</td><td>Customer Name</td></tr>');

            $.each(data.d.results, function (key, val) {

                items.push('<tr id="' + val.BdcIdentity + '"><td>' +

                    val.CustomerID + '</td><td>' +

                    val.ContactName + '</td></tr>');

            });

            items.push("</table>");

            $("#displayDiv").html(items.join(''));

        }

    }

    ExecuteOrDelayUntilScriptLoaded(getCustomers, "sp.js");

});

function getCustomers() {

    var grid = new AppLevelECT.Grid($("#displayDiv"), _spPageContextInfo.webServerRelativeUrl);

    grid.init();

}

AppLevelECTB2 -> Right Click -> Deploy

Thank You.