The Daily Parker

Politics, Weather, Photography, and the Dog

6,000

This month will see two important Daily Parker milestones. This is the first one: the 6,000th post since braverman.org launched as a pure blog in November 2005. The 5,000th post was back in March 2016, and the 4,000th in March 2014, so I'm trucking along at just about 500 a year, as this chart shows:

Almost exactly four years ago I predicted the 6,000th post would go up in September. I'm glad the rate has picked up a bit. (New predictions: 7,000 in May 2020 and 10,000 in April 2026.)

Once again, thanks for reading. And keep your eyes peeled for another significant Daily Parker milestone in a little less than two weeks.

All caught up

Two weeks ago I started writing my A-to-Z posts and got all the way to today's before my life became nuts—as I knew it would—with 4 chorus-related events and a huge increase in my work responsibilities. And with the Apollo After Hours benefit this coming Friday, this weekend will be pretty full as well.

I use my email inbox as a to-do list, and right now it has 35 messages, 30 of which relate to the benefit. I'm very glad the A-to-Z Challenge gives us Sundays off, because I don't know how I'm going to get another week ahead by tomorrow night.

The performances were worth it, though.

I is for Interface

Blogging A to ZDay 9 of the Blogging A-to-Z challenge brings up one of the key concepts in object-oriented design: the interface.

In object-oriented design, rule #1 is "program to interfaces, not to implementation." In other words, when interacting with an object in your system, you should care about what behaviors and data you need to use, not what the object actually does with them.

Going back to last week's room-and-window example: the original problem was that I want to close all the windows in the house with one method call. The solution on Saturday involved having a Room class that exposed a list of Window objects which you could iterate over and call the Close() method on each.

That's great, but what if I want to close all the windows, doors, fireplaces, and anything else that I can close, because of the zombie apocalypse? In Saturday's implementation, I need to know that rooms have windows, doors, fireplaces, and other things specifically. That is, I need to know how each room is implemented.

I really don't care whether the thing is a window, a door, or a squirrel's mouth; I want it closed now, before the zombies get in.

So let's do this instead: define the behavior of a thing that I can close, and operate on the behavior rather than the thing itself. In C#, I can define an interface, which would look like this (and refer back to Saturday or the code sample file for the rest of the implementation):

namespace InnerDrive.DailyParkerAtoZ.WeekOne
{
    public interface ICloseable
    {
	    void Close();
    }
}

That defines a single behavior that a class can do. (Interfaces can also define data and events, but that's beyond the scope of this post.)

Now I can add the interface to the Window class:

public class Window : ICloseable
{
	public void Close() { }
	public void Open() { }
}

And then refactor the Room class so that you can add and close all manner of closeable things:

public class Room
{
	public void Add(ICloseable closeable)
	{
		_closeableThings.Add(closeable);
	}

	public void CloseEverything()
	{
		foreach (var thing in _closeableThings)
		{
			thing.Close();
		}
	}

	public IEnumerable<ICloseable> Windows => 
		new List<ICloseable>(_closeableThings.Where(p => p is Window));

	private readonly List<ICloseable> _closeableThings = new List<ICloseable>();
}

Well, that looks different. Instead of adding windows to a room, I can now add anything that can be closed. And because of that, at lines 16 and 17, in order to make sure the Windows list still works, I have to change the code so it only returns windows.

It's still a dumb piece of code, but you can start to see how powerful interfaces are. If in the future I create some new class with a Close() method, I can apply the ICloseable interface to it and stick it in a room. (Books, maybe? Escrow accounts? People named Glenn?)

There are many, many implications to all of this. But this is one of the foundations of OO design. I don't care what the thing is, I care what it does or knows. Program to interfaces, not to implementations.

Parker doing much better

Yesterday Parker got fitted for a new E-collar after I discovered that his long nose and long tongue were just long enough to lick his sutures. Fortunately the incision doesn't seem irritated or infected, probably owing to the massive doses of antibiotics we've got him on.

As for the primary injury, that seems to have healed remarkably well in the few days since his surgery. He's putting more weight on the leg, and has less trouble standing up. He still seems a little shaky in some postures, particularly squatting.

So Parker's biggest problems right now are bumping into things with his Cone of Shame, and the abject boredom of a smart dog getting only 15 minutes of walkies a day.

He's really going to hate this coming week, too. I've got rehearsals or performances every single evening, so he'll be alone most of the time. Poor dude.

(There is no A-to-Z post today because it's Sunday.)

G is for Generics

Blogging A to ZFor day 7 of the Blogging A-to-Z challenge, I'm going totally generic.

A generic in C# allows your code to "defer the specification of one or more types until the class or method is declared and instantiated by client code." In other words, you can declare a class that takes a type to be named later.

Imagine you have a program that represents a house. Your house has rooms, and the rooms have windows, doors, and in some cases, fireplaces. They also have furniture. And sometimes headless corpses. (Don't ask.)

If you were using C# 1.0, you'd need to design structures to hold all of these things, and you'd probably wind up using arrays, like this:

#region Copyright ©2002 Inner Drive Technology

using System.Collections;

#endregion

namespace InnerDrive.DailyParkerAtoZ.WeekOne
{
	public class Window
	{
		public void Close() { }
		public void Open() { }
	}


	public class RoomV1
	{
		public void Add(Window window)
		{
			_windows.Add(window);
		}

		public IEnumerable Windows
		{
			get
			{
				return new ArrayList(_windows);
			}
		}

		private readonly ArrayList _windows = new ArrayList();
	}
}

The only problem is...you don't really know for sure whether the things going into or coming out of the _windows array list are actually windows. That's because the System.Collections.ArrayList class only stores objects, not specific kinds of objects.

Generics allow you to impose type safety on the collection of windows through the use of a type parameter. Now you can do this:

public class Room
{
	public void Add(Window window)
	{
		_windows.Add(window);
	}

	public IEnumerable<Window> Windows => new List<Window>(_windows);

	private readonly List<Window> _windows = new	List<Window>();
}

(Notice also the nifty shorthand on line 8 that eliminates the get method.)

This works because the List<T> class takes any object type for T, leaving it up to the compiler to work out what type it should contain. The prototype for the class looks something like this:

public class List<T>
{
	public void Add(T input) { }
}

The type parameter T can be anything. (You can restrict what T can contain, which I will leave as an exercise for the reader.)

Generics simplify a lot of programming tasks. But just wait until Tuesday when I show you how to make object-oriented designs really fly in C#.

Housekeeping note: The A-to-Z Challenge takes Sundays off. The next post in this series will be on Monday. Enjoy your weekend!

E is for Encapsulation

Blogging A to ZWelcome to day 5 of the Blogging A-to-Z challenge.

In object-oriented design, we talk about a number of basic concepts that make code easier for humans to read and maintain. Encapsulation is fundamental, by hiding the internal data of a class so that only the class can use it. To access data within the class, you can't just reach in and grab it; you need to use the public properties and methods of the class.

Here's a stupid class:

#region Copyright ©2018 Inner Drive Technology

using System;
using System.Collections.Generic;

#endregion

namespace InnerDrive.DailyParkerAtoZ.WeekOne
{
	public class Encapsulation
	{
		public string Name { get; private set; }

		public void ChangeName(string newName)
		{
			if (string.IsNullOrWhiteSpace(newName))
			{
				throw new ArgumentException("Name must have a value", nameof(newName));
			}
			Name = newName;
			_names.Add(newName);
		}

		internal void Clear()
		{
			Name = string.Empty;
		}

		public IEnumerable<string> NameList => new List<string>(_names);

		private readonly List<string> _names = new List<string>();
	}
}

Seriously, this is dumb. But it demonstrates some of the ways C# encapsulates data.

Line 12 creates a property called Name that any code anywhere can call, because it's public. But it also declares a setter method that is private, meaning only the Encapsulation class itself can set the value of Name.

Lines 14-22 show how this works. The ChangeName method first makes sure you are giving it a real value, then changes Name and adds the new name to a list of names that is itself private. So the only way to change Name is to use the ChangeName method. (There's another way to do this in the property setter, but I wanted to show how this works exactly.)

Lines 24-27 provide you a way of clearing Name, but the method is marked internal. That means only classes in the same assembly can use this method, which has consequences for our unit tests, below.

Line 29 does a nifty trick where, instead of actually giving outside code access to its private list of _names (line 31), it creates a copy of the list and sends that out. Otherwise, anyone would be able to change the contents of _names just by using the NameList property.

Now here's the unit test code:

#region Copyright ©2018 Inner Drive Technology

using System.Linq;
using InnerDrive.DailyParkerAtoZ.WeekOne;
using Microsoft.VisualStudio.TestTools.UnitTesting;

#endregion

namespace InnerDrive.DailyParkerAtoZ.UnitTests
{
	[TestClass]
	public class EncapsulationTests
	{
		[TestMethod]
		public void CanSetNameOfObject()
		{
			var thing = new Encapsulation();
			//thing.Name = "This won't compile";
			//thing._names.Add("This won't compile either");
			thing.ChangeName("Ernie");
			Assert.AreEqual("Ernie", thing.Name);
			Assert.AreEqual(1, thing.NameList.Count());
		}

		[TestMethod]
		public void CanClearNames()
		{
			var thing = new Encapsulation();
			thing.ChangeName("Ernie");
			Assert.AreEqual("Ernie", thing.Name);
			Assert.AreEqual(1, thing.NameList.Count());

			// thing.Clear(); // oops—won't compile!

			// Assertions fail!
			Assert.IsTrue(string.IsNullOrWhiteSpace(thing.Name));
			Assert.AreEqual(1, thing.NameList.Count());
		}
	}
}

The comments explain what's going on.

So how can we test the Encapsulation.Clear() method? By adding this line to the InnerDrive.DailyParkerAtoZ.WeekOne.AssemblyInfo.cs file:

[assembly: InternalsVisibleTo("InnerDrive.DailyParkerAtoZ.UnitTests")]

Now all of the objects, properties, and methods in the WeekOne assembly marked internal are visible to the unit test class, and the tests pass.

Cool, right?

As always, the growing Visual Studio solution is here. The ZIP file contains the complete Git log of the project, by the way. Enjoy.

Parker update: home but on drugs

Cone of shame, shaved leg, drugged out of his mind: that's my boy. But at least he's home:

As I've been saying, the next few weeks will be rough. But he's going to get lots of attention, especially between now and Monday.

And then there's this:

He has physical pain, I have psychic pain. All because he ran up some stairs too fast.

Again: ouch.

D is for Database

Blogging A to ZWelcome to day 4 of the Blogging A-to-Z challenge. After yesterday's more theoretical post on the CLR, today will have a practical example of how to connect to data sources from C# applications.

Almost every application ever written needs to store data somewhere. If you're deploying a .NET website into Microsoft Azure (like this blog), you will probably connect it to an Azure SQL Database. Naturally, Visual Studio and C# make this pretty easy.

Here's the code that opens up a database connection and prints out to the Trace window what it's opened:

#region Copyright ©2018 Inner Drive Technology

using System.Configuration;
using System.Data.SqlClient;
using System.Diagnostics;

#endregion

namespace InnerDrive.DailyParkerAtoZ.WeekOne
{
	public static class DataConnections
	{
		private static string ConnectionString => ConfigurationManager.ConnectionStrings["Database"].ConnectionString;

		public static void Connect()
		{
			using (var connection = new SqlConnection(ConnectionString))
			{
				connection.Open();
				Trace.WriteLine($"Connected to {connection.DataSource}");
			}
		}
	}
}

Let's take a look at that line by line.

Lines 3-6 tell the compiler that the objects referenced in the executable code come from those four namespaces (which I'll talk more about on April 16th). The SqlConnection class, for example, lives in the System.Data.SqlClient namespace. If I didn't have the using statement on line 5, I'd have to reference the class and its namespace as System.Data.SqlClient.SqlConnection, which is cumbersome.

Line 13 creates a ConnectionString property that gets its value from a configuration setting. More on that below.

Line 17 first sets up a different kind of using statement, which makes sure that whatever the expensive SqlConnection class does while its alive, it gets cleaned up when it finishes on line 21—even if it throws an exception. Then the same line creates a new SqlConnection object and assigns it to the variable connection.

Line 19 attempts to open the connection to the database. If it succeeds, line 20 prints out the name of the data source. If it fails, it throws an exception that whatever method called this one can catch.

The configuration file looks like this (but with a real database, user ID, and password):

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
	<connectionStrings>
		<add 
			name="Database" 
			connectionString="server={server name}.database.windows.net;initial catalog={database name};persist security info=True;user id={user ID};password={password};"
		/>
	</connectionStrings>
</configuration>

Notice that the name on line 5 corresponds to the configuration setting name on line 13 of the C# code. That's how the code knows which connection string to read from configuration.

Finally, there's also a unit test, which looks like this:

#region Copyright ©2018 Inner Drive Technology

using InnerDrive.DailyParkerAtoZ.WeekOne;
using Microsoft.VisualStudio.TestTools.UnitTesting;

#endregion

namespace InnerDrive.DailyParkerAtoZ.UnitTests
{
	[TestClass]
	public class DataConnectionsTests
	{
		[TestMethod]
		public void CanConnectToDataSource()
		{
			DataConnections.Connect();
		}
	}
}

If the call to DataConnections.Connect() succeeds, the test passes. If the call fails, the test fails and shows the exception that gets thrown.

You can download the code for all of these posts here. You'll have to change the configuration information in the unit test project's app.config file to make it work, of course.