Tips and tricks in C# .NET
April 7, 2015 1 Comment
Indexers are used extensively when accessing items in an array or List:
Friend f = friends[2];
It’s fairly easy to implement your own indexer. Imagine a table with guests sitting around. We could implement an indexer to easily access guest #n.
The Guest object is simple with only one property:
public class Guest
{
public string Name { get; set; }
}
April 5, 2015 1 Comment
Introduction
In the previous post we dived into Postgresql statement execution on a RedShift cluster using C# and ODBC. We saw how to execute a single statement or many of them at once. We also tested a parameterised query which can protect us from SQL injections.
In this post we’ll deviate from .NET a little and concentrate on the basics of data warehousing and data mining in RedShift. In particular we’ll learn about a popular schema type often used in conjunction with data mining: the star schema.
Star and snowflake schemas
I went through the basic characteristics of star and snowflake schemas elsewhere on this blog, I’ll copy the relevant parts here.
April 3, 2015 3 Comments
It’s trivial to create a temporary file using the Path class in .NET. Let’s first see how to find the path to the current user’s temp folder:
string tempFolderPath = Path.GetTempPath();
In my case it returns C:\Users\andras.nemes\AppData\Local\Temp\ which is the same as the value of the TEMP environment variable at the user level on my PC.
April 2, 2015 3 Comments
Introduction
In the previous post we tested how to connect to the master node in code using the .NET AWS SDK and ODBC. We also executed our first simple Postgresql remotely. In this post we’ll continue in those tracks and execute some more Postgresql statements on our master node.
Preparation
We’ll execute most of the scripts we saw in this blog post. Prepare a text file called postgresscript.txt with the following content and save it somewhere on your harddrive:
April 1, 2015 2 Comments
As you know primitive numeric types in C# – and other modern programming languages – have maximum and minimum values that can be stored in memory. If you’re trying to store a larger number in the variable then you’ll get an overflow with unexpected results.
Let’s see an example with the “byte” type. It is actually not one of the primitive types, like int or long, but simply a keyword for an integral type to store the numbers 0-255. Why 255? 1 byte consists of 8 bits and 8 bits in the computer’s memory allows us to store 255 as the highest number. 255 in binary is all 1’s for all 8 bits:
11111111
What happens if we add 1 to that? On paper we can easily solve it by some basic binary maths:
11111111
+ 00000001
===========
100000000
March 31, 2015 1 Comment
.NET has a fairly large number of built-in string formatters that you can pass into the string.Format method. Here are some examples from the MSDN page about formatting:
String.Format("{0,-12}{1,8:yyyy}{2,12:N0}{3,8:yyyy}{4,12:N0}{5,14:P1}",
city.Item1, city.Item2, city.Item3, city.Item4, city.Item5,
(city.Item5 - city.Item3)/ (double)city.Item3);
String.Format("{0,-12}{1,8}{2,12}{1,8}{2,12}{3,14}\n",
"City", "Year", "Population", "Change (%)");
String.Format("{0,-10:C}", 126347.89m);
The IFormatProvider and ICustomFormatter interfaces will provide you with the methods required to create your own formats.
March 30, 2015 5 Comments
Introduction
In the previous post we went through some basic C# code to communicate with Amazon RedShift. We saw how to get a list of clusters, start a new cluster and terminate one using the .NET AWS SDK.
We haven’t yet seen how to execute Postgresql commands on RedShift remotely from code. That is the main goal of this post.
Installing the ODBC driver
In this section we’ll prepare our Windows environment to be able to connect to RedShift using ODBC. At times this can be a frustrating experience so I’ll try to give you as much detail as I can.
March 27, 2015 1 Comment
The largest integer that can be stored in a long, i.e. a 64-bit integer is 9,223,372,036,854,775,807 in .NET. That is a very large number that will be enough for most applications out there.
However, sometimes it’s not enough and you need to handle something larger. This article on Wikipedia shows several use cases where this can occur. .NET also provides the float and double numeric types that provide much larger ranges. They won’t be integers exactly but they may suit your needs anyhow.
The .NET framework has an object called BigInteger that lets you construct arbitrarily large integers. This object resides in the System.Numerics namespace so you’ll need to reference the System.Numerics.dll library.
March 26, 2015 Leave a comment
Introduction
In the previous post we looked into how to connect to the Amazon RedShift master node using a tool called WorkBenchJ. We also went through some very basic Postgresql statements and tested an equally basic aggregation script.
In this post we’ll install the .NET SDK and start building some test code.
Note that we’ll be concentrating on showing and explaining the technical code examples related to AWS. We’ll ignore software principles like SOLID and layering so that we can stay focused. It’s your responsibility to organise your code properly. There are numerous posts on this blog that take up topics related to software architecture.
Installing the SDK
March 25, 2015 1 Comment
In this post we saw how to extract the byte array representation of primitive types in C#. Here we’ll look at how to do the same with DateTime objects.
DateTimes are not primitive types so the BitConverter.GetBytes method has no overload for it. Therefore we’ll need to go through some more steps. We’ll convert the date into its 64-bit (long) representation. The long can then be supplied to the GetBytes method:
DateTime utcNow = DateTime.UtcNow; long utcNowAsLong = utcNow.ToBinary(); byte[] utcNowBytes = BitConverter.GetBytes(utcNowAsLong);
utcNowAsLong is a very large integer. It was 5247234542978972986 at time of running the code example. Then we get the bytes using GetBytes which will return a byte of 8 elements as a long is a 64-bit / 8-byte integer.
The reverse operation mirrors what we did above:
long utcNowLongBack = BitConverter.ToInt64(utcNowBytes, 0); DateTime utcNowBack = DateTime.FromBinary(utcNowLongBack);
“utcNowBack” and the original “utcNow” will be set to the same time.
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