I recently made two contributions to
the Agatha Project by Davy Brion over on Google Code, and one of
the things I wanted to follow up with was a post showing examples and some, seemingly required tid bits.
The contributions which I made where: To support StructureMap To include REST (JSON and XML) support for
the service contract
The examples which I have made, I want to format them so they fit in with
the current format of examples over on Agatha and hopefully create and submit a third patch which will include these examples to help others who wish to use these additions. Whilst building these examples for both XML and JSON I have learnt a couple of things which I feel are not really well documented, but are extremely good practice and once known make perfect sense. I have chosen a real basic e-commerce context for my example Requests and Responses, and have also made use of
the excellent tool AutoMapper, again on Google Code. Setting
the scene I have followed
the Pipes and Filters Pattern with
the IQueryable interface on my Repository and exposed
the following methods to query Products: IQueryable<Product> GetProducts();
IQueryable<Product> ByCategoryName(this IQueryable<Product> products, string categoryName)
Product ByProductCode(this IQueryable<Product> products, String productCode)
I have an interface for
the IProductRepository but for
the concrete implementation I have simply created a protected getter which populates a private List<Product> with 100 test products with random data. Another good reason for following an interface based approach is that it will demonstrate usage of my first contribution which is
the StructureMap support. Finally
the two Domain Objects I have made are Product and Category as shown below:
public class Product
{
public String ProductCode { get; set; }
public String Name { get; set; }
public Decimal Price { get; set; }
public Decimal Rrp { get; set; }
public Category Category { get; set; }
}
public class Category
{
public String Name { get; set; }
}
Requirements for
the REST Support
One of
the things which you will notice with Agatha is that you do not have to decorate your Request and Response objects with
the WCF Service Model Attributes like DataContract, DataMember etc… Unfortunately from what I have seen, these are required if you want
the same types to work with your REST endpoint. I have not tried but I assume
the same result can be achieved by simply decorating
the same classes with
the Serializable Attribute. Without this
the operation will fail.
Another surprising
thing I have found is that it did not work until I used
the following Attribute parameters:
Name
Namespace
e.g.
[DataContract(Name = "GetProductsRequest", Namespace = "AgathaRestExample.Service.Requests")]
public class GetProductsRequest : Request
{
}
Although I was surprised by this, things kind of explained themselves when I got round to figuring out
the exact construct required for both
the XML and
the REST. One of
the things which you already know and are then reminded of is that each of your Requests and Responses ultimately inherit from an abstract base class respectively. This information needs to be represented in a way native to
the format being used. I have seen this in XML but I have not seen
the format which is required for
the JSON.
JSON Consumer Example
I have used JQuery to create
the example and I simply want to make two requests to
the server which as you will know with Agatha are transmitted inside an array to reduce
the service calls. I have also used a tool called json2 which is again over at Google Code simply to convert my JSON expression into its string format for transmission. You will notice that I specify
the type of Request I am using and
the relevant Namespace it belongs to. Also notice that
the second request has a parameter so each of these two object are representing an abstract Request and
the parameters of
the object describe it.
<script type="text/javascript">
var bodyContent = $.ajax({
url: "http://localhost:50348/service.svc/json/processjsonrequests",
global: false,
contentType: "application/json; charset=utf-8",
type: "POST",
processData: true,
data: JSON.stringify([
{ __type: "GetProductsRequest:AgathaRestExample.Service.Requests" },
{ __type: "GetProductsByCategoryRequest:AgathaRestExample.Service.Requests", CategoryName: "Category1" }
]),
dataType: "json",
success: function(msg) {
alert(msg);
}
}).responseText;
</script>
XML Consumer Example
For
the XML Consumer example I have chosen to use a simple Console Application and make a WebRequest to
the service using
the XML as a request. I have made a crude static method which simply reads from an XML File, replaces some value with a parameter and returns
the formatted XML. I say crude but it simply shows how XML Templates for each type of Request could be made and then have a wrapper utility in whatever language you use to combine
the requests which are required.
The following XML is
the same Request array as shown above but simply in
the XML Format.
<?xml version="1.0" encoding="utf-8" ?>
<ArrayOfRequest xmlns="http://schemas.datacontract.org/2004/07/Agatha.Common" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
<Request i:type="a:GetProductsRequest" xmlns:a="AgathaRestExample.Service.Requests"/>
<Request i:type="a:GetProductsByCategoryRequest" xmlns:a="AgathaRestExample.Service.Requests">
<a:CategoryName>{CategoryName}</a:CategoryName>
</Request>
</ArrayOfRequest>
It is funny because I remember submitting a question to StackOverflow asking whether there was a REST Client Generation tool similar to what Microsoft used for their RestStarterKit but which could be applied to existing services which have REST endpoints attached. I could not find any but this is now definitely something which I am going to build, as I think it is extremely useful to have but also it should not be too difficult based on
the information I now know about
the above. Finally I thought that
the Strategy Pattern would lend itself really well to this type of
thing so it can accommodate for different languages.
I think that is about it, I have included
the code for
the example Console app which I made below incase anyone wants to have a mooch at
the code. As I said above I want to reformat these to fit in with
the current examples over on
the Agatha project, but also now thinking about it, make a Documentation Web method…{brain ticking} :-)
Cheers for now and here is
the final bit of code:
static void Main(string[] args)
{
var request = WebRequest.Create("http://localhost:50348/service.svc/xml/processxmlrequests");
request.Method = "POST";
request.ContentType = "text/xml";
using(var writer = new StreamWriter(request.GetRequestStream()))
{
writer.WriteLine(GetExampleRequestsString("Category1"));
}
var response = request.GetResponse();
using(var reader = new StreamReader(response.GetResponseStream()))
{
Console.WriteLine(reader.ReadToEnd());
}
Console.ReadLine();
}
static string GetExampleRequestsString(string categoryName)
{
var data = File.ReadAllText(Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location), "ExampleRequests.xml"));
data = data.Replace("{CategoryName}", categoryName);
return data;
}
}
