Skip to main content

Improving “Boiler Plate” Data-Reader Code – Part 4

In part 3 we created a SQL repository object that took a populated instance of IQuery to select/return an enumerable list of objects. A limitation of the repository was that the query had to be text based, it couldn't handle stored procedures and/or parameters. By incorporating an abstract factory pattern we can extend the functionality to handle different types of query.

The original code inside "SqlRepository.Get(...)" needs to be changed from:

using (var command = connection.CreateCommand())
{
command.CommandText = query.Text;
 
connection.Open();

To:

using (var command = connection.CreateCommand())
{
var handler = QueryHandlerFactory.Create(query);
handler.Assign(command, query);
 
connection.Open();

The static factory class takes an instance of IQuery and determines which "query handler" to return depending upon the additional interface that the "passed in" query implements. This is implemented via the following code:

public static class QueryHandlerFactory
{
public static IHandleAQuery Create(IQuery query)
{
if (query is IDefineCommmandTextQuery)
{
return new HandleCommandTextQuery();
}
 
var ex = new NotSupportedException();
ex.Data.Add("IQuery Type", query.GetType());
throw ex;
}
}

To finish off the implementation the following new interfaces and code are needed:

public interface IDefineCommmandTextQuery : IQuery
{
string Text { get; }
}
 
public interface IHandleAQuery
{
void Assign(SqlCommand command, IQuery query);
}
 
public class HandleCommandTextQuery : IHandleAQuery
{
public void Assign(SqlCommand command, IQuery query)
{
command.CommandType = CommandType.Text;
command.CommandText = ((IDefineCommmandTextQuery)query).Text;
}
}

Finally we simplify the IQuery interface as it's only property has now been moved up into IDefineCommandTextQuery and then update all concrete implementations of "IQuery" to "IDefineCommandTextQuery " as well, without these final changes the factory class will not be able to correctly determine the handler from the interface that is implemented.

public interface IQuery
{
}
 
public class GetAllCustomersQuery : IDefineCommmandTextQuery
{
public string Text
{
get
{
return "SELECT id, Firstname, Surname FROM Customer";
}
}
}

Now our code can be safely extended to handle different query types just be creating the new implementation of the query handler and modifying the factory to handle the identification and creation of the new type. Part 5 will show how this functionality can be extended to handle stored procedures with parameters.

Comments

Popular posts from this blog

Mocking HttpCookieCollection in HttpRequestBase

When unit testing ASP.NET MVC2 projects the issue of injecting HttpContext is quickly encountered.  There seem to be many different ways / recommendations for mocking HttpContextBase to improve the testability of controllers and their actions.  My investigations into that will probably be a separate blog post in the near future but for now I want to cover something that had me stuck for longer than it probably should have.  That is how to mock non abstract/interfaced classes within HttpRequestBase and HttpResponseBase – namely the HttpCookieCollection class.   The code sample below illustrates how it can be used within a mocked instance of HttpRequestBase.  Cookies can be added / modified within the unit test code prior to being passed into the code being tested.   After it’s been called, using a combination of MOQ’s Verify and NUnit’s Assert it is possible to check how many times the collection is accessed (but you have to include the set up calls) and that the relevant cookies have …

Do "Task Hours" add anything in Scrum (Agile)?

What do task hours add to the overall process in scrum?This was a question that has arisen from all team members in both instances that I've helped teams switch over to scrum. The benefits of artifacts like the comparative story point estimation, the 2 week sprints, stand-ups and the end of sprint demo have been self evident to the team, but as one I think every team member has expressed dismay when it comes to task planning and estimating each task in hours. Left unchecked there is a natural tendency for people to actually begin to dread the start of each sprint purely due to the task planning session.In my current role we've been lucky to investigate this further as a team.The team sat down to discuss the problems it was experiencing with estimating tasks in hours and the following common themes appeared:It is hard: Maybe it shouldn't be, but time estimation is hard! Story points are comparative and abstracted making them easier to determine, but time estimate is gen…

Why do my Android Notification only appear in the status bar?

I'm definitely getting back into Android development, I'm remembering that feeling of 'Surely this should be easier than this!'. All I wanted to do was to schedule a local notification which behaved similar to a push notification pop-up. That is, as well as showing the small icon in the status bar I wanted it to pop up on screen to notify the end user. All seems fairly easily, I found this code for how to schedule a notification. That all worked perfectly, apart from the notification would only appear in the status bar. Searching around I found loads of different answers / solutions, mostly all saying the same thing:It only worked if you used 'NotificationCompat.Builder' in place of 'Notification.Builder', orYou had to set the priority to 'NotificationCompat.PRIORITY_HIGH'As usually happens, none of these solutions worked for me until I added in the missing piece of the jigsaw:- '.setDefaults(Notification.DEFAULT_ALL)'. For me this…