Accept Data With A Webservice C# .NET 3.5

Question

I was curious as to how I would accomplish the following with webservices:

1. Authenticate a user.
2. Accept a CSV or XML file.
3. Process the file and put it into an SQL database.

Someone mentioned in a previous post that I should use a webservice. I can't seem to find any resources that explain how to begin something like this. All the simple examples seem to just show how you can serve XML given a query.

I want to know how to accept stuff and also, how this would differ from an upload control on an authenticated webpage. I don't think I really understand webservices and their benefits.

How would the user sending the XML file interface with my webservice?

Answer 1

If you want to do large file uploads, then a web service may cause some issues, because some web service platforms (including .NET) have default settings limiting the size of the data. The advantage of a web service is that it does all the mapping of the request to/from XML, so you can return a .NET type, and don't need to muck around with processing request parameters. However, you may have to put more effort into maintaining state, etc. For logins, what you can do is have a login function that returns some kind of identifier which can be used to verify the user as valid for that session - one way of doing this being to have columns in your user table for lastActive and sessionGUID, and when they log in you generate a new sessionGUID and return that, and on that and any other valid request they make you update the lastActive, and if there is a request too long after the lastActive time, then you refuse the request... there's any number of similar ways of doing that, but hopefully you get the general idea - you don't want to require the login details each time, but you can generate a temporary identifier and use that. For accepting an XML file, you'd want to use something like XDocument or XMLReader to read the data that you receive. Assuming you're not talking about the parsing of the XML format that the web service itself uses, you're most likely to be receiving a string and then pushing that into an XDocument and then using the standard XDocument functions to process the data. If the document would be large, then XMLReader should be more efficient. For reading a CSV file, there are some (free and non-free) CSV readers which help avoid some of the issues you can have, giving you a nice API for processing a string or strings of CSV data. If you know that the source data doesn't have non-structural commas, though, you can just take the string and split it by commas, and then strip any quotes around the values. That tends to get flaky quite fast if there might be addresses or other data that could have commas in, though. The XML should be able to be passed via the web service just fine - it should be encoded and decoded, so it's then compliant strings being passed out.

As for storing it in a database, there's any number of ways to do that - you can use ADO.NET to store things in a database without further libraries, you can create a database structure in Visual Studio or SQL Server Management Studio and then use SQLMetal or Linq to SQL to generate classes for saving the data, you can use a 3rd party database mapping tool (such as Castle ActiveRecord), or whatever. It depends what you know and how much you're willing to learn. That's really separate to the web service. When you define a web service in .NET you effectively define standard functions with attributes marking them as web services, so the database side is standard .NET database stuff that's not necessarily any different to what you'd do for an ASP.NET website, or even a desktop program.

Answer 2

A web service is not really appropriate for sending an arbitrary file. It can be done, but if that's your only reason for creating the web service, you might as well just stick to HTTP.

If the file has a specific format or specific contents then you might want to create a web service for that. The purpose of an ASMX or WCF web service is to provide discoverability and strong typing to the data (among other things, but I'm sticking to the basics for the moment). From the perspective of the client, instead of trying to create some ugly XML or CSV blob and chuck it over HTTP, you use an actual service proxy with POCO classes:

MyService service = new MyService();
MyData data = new MyData() { ID = 3, Name = "Test", Date = DateTime.Now };
service.Save(data);

Visual Studio (and equivalent tools in Java and some other platforms) will take care of generating the proxy for you, so really all you have to do is write the above code.

But if you're just trying to send any data, this won't get you anywhere, because you can't generate a proxy for raw XML. Well, you can, but it would just be an XmlDocument and that accomplishes nothing in terms of usability, type safety or discoverability.

Don't get confused by the "XML" in "XML Web Service". It's not a tool for sending around vanilla XML. Rather, XML refers to the format of the message, as it is transmitted over the wire, as opposed to a POST string (id=3&name=Test&date=2010-01-24) or a binary RPC call as used in .NET Remoting.

In terms of authentication, if you do decide to use WCF, you just have to use the right binding. A WCF proxy is normally configured by default to use wsHttpBinding, which uses integrated Windows authentication to secure the messages. Again, assuming you use Visual Studio, this is all done pretty much automatically for you unless you decide to change the defaults.