Using the StringComparer class for string equality with C# .NET

May 12, 2015 1 Comment

In this post we saw how to use the generic IEqualityComparer of T interface to indicate equality for our custom types. If you need a similar comparer for strings then there’s a ready-made static class called StringComparer which can construct string comparers for you.

The StringComparer class provides comparers for the common string comparison scenarios: ordinal, locale specific and invariant culture comparisons. This is a good MSDN article on the differences between these.

Read more of this post

Filed under .NET, C# language features Tagged with ,

SOLID principles in .NET revisited part 6: the Interface Segregation Principle

May 11, 2015 4 Comments

Introduction

In the previous post we continued to discuss the Liskov Substitution Principle. We saw a subtle example of breaking LSP by trying to force an object to implement an interface even though not all methods of the interface made sense for it. The client object, i.e. OnDemandAgentService cannot consume all implementations of IAuthorizationService without fully being able to carry out its tasks.

A possible solution comes in the form of letter ‘I’ in SOLID, which stands for the Interface Segregation Principle (ISP). ISP states that clients should not be forced to depend on interfaces and methods they do not use. Applying ISP correctly will result in a lot of small interfaces instead of handful of large ones with lots of methods. The more methods to an interface has the more likely it is that an implementation will not be able to fulfil all parts of the contract. The IAuthorizationService only has 2 methods and we immediately found an example where a class, the AuthorizationService only could implement one of them.

Read more of this post

Filed under .NET, Design patterns, Design principles Tagged with , , , ,

Using Amazon DynamoDb for IP and co-ordinate based geo-location services part 10: querying the coordinate range table

May 10, 2015 1 Comment

Introduction

In the previous post we loaded the limited lng/lat range records into DynamoDb. As we’re only talking about about 50 records we could have added them in code one by one. However, that strategy would never work for the full MaxMind data set even after discarding the duplicates. So instead we looked at the built-in Import/Export functionality in DynamoDb. You’ll be able to go through the same process when you’re ready to import the full data set.

In this post we’ll see how to query the lnglat range database to extract the ID of the nearest geolocation. We’ll get to use the AWS Java SDK.

Read more of this post

Filed under Amazon, Java Tagged with , , , , ,

Using Amazon DynamoDb for IP and co-ordinate based geo-location services part 9: uploading the co-ordinate range to DynamoDb

May 9, 2015 Leave a comment

Introduction

In the previous post we successfully created the lng/lat import file that DynamoDb can understand and process.

In this post we’ll upload this file to DynamoDb. The process will be the same to what we saw in this post where we inserted the demo data into the IPv4 range table. If necessary then re-read that post to refresh your memory about the process. We’ll follow the strategy we laid out in this post.

Read more of this post

Filed under Amazon, Java Tagged with , , , , ,

Implementing equality of reference types by overriding the == operator with C# .NET

May 8, 2015 1 Comment

In this post we saw how to implement the generic IEquatable interface to make two custom objects equatable using the static Equals method.

You’re probably aware of the equality operator ‘==’ in C#. Let’s see what happens if you try to use it for a custom object:

public class Person
{
	public int Id { get; set; }
	public string Name { get; set; }
	public int Age { get; set; }
}

Read more of this post

Filed under .NET, C# language features Tagged with ,

SOLID principles in .NET revisited part 5: the Liskov Substitution Principle 2

May 7, 2015 1 Comment

Introduction

In the previous post we looked at letter ‘L’ in SOLID, i.e. the Liskov Substitution Principle. We saw how adhering to the LSP helps remove implementation-specific details from a client class that consumes those implementations. The client class will be able to consume the services of an abstraction without worrying about the actual implementation of the abstraction. The goal of LSP is that any implementation of an abstraction will work seamlessly within the consuming class.

We looked at the following cases that can indicate a violation of LSP:

  • switch or if-else blocks checking for the value of an enumeration
  • Code blocks that check the actual type of an abstraction to branch logic. This can be coupled with downcasting the abstraction to a concrete implementation type
  • Blocks with magic strings that check for a value in some string parameter and branch logic accordingly

There’s at least one more indicator which we haven’t seen so far. I decided to devote a separate article to that case as it brings us closer to the next constituent of SOLID, i.e. the Interface Segregation Principle.

Read more of this post

Filed under .NET, Design patterns, Design principles Tagged with , , , ,

Implementing the IEqualityComparer of T interface for object equality with C# .NET

May 6, 2015 2 Comments

The generic IEqualityComparer of T provides you a way to indicate whether two custom objects are equal. We’ve looked at equality in a number of posts on this blog – see the link below if you’re curious – and IEqualityComparer fulfils a similar purpose though its usage is different.

Equality comparers are most often used to filter out duplicates from a collection.

Consider the following class:

Read more of this post

Filed under .NET, C# language features Tagged with ,

Implementing the IEquatable of T interface for object equality with C# .NET

May 5, 2015 5 Comments

In this short post we’ll see a way how to make two custom objects equatable using the generic IEquatable interface. Consider the following object:

public class Person
{
	public int Id { get; set; }
	public string Name { get; set; }
	public int Age { get; set; }
}

The object superclass has an Equals method that we can test as follows:

Read more of this post

Filed under .NET, C# language features Tagged with ,

SOLID principles in .NET revisited part 4: the Liskov Substitution Principle

May 4, 2015 1 Comment

Introduction

In the previous post we looked at the Open-Closed Principle, i.e. ‘O’ in the SOLID acronym. We saw how the OCP facilitated the flexibility and extensibility of a class. It also places a constraint on a class by making it “append-only”. In other words you can extend a class but you cannot change the implementation of existing parts of a class.

In this post we’ll take a look at letter ‘L’ which stands for the Liskov Substitution Principle LSP.

Definition of LSP

LSP stands for the interchangeability of different implementations of an abstraction. An abstraction in C#, and probably most other popular object-oriented programming languages, can either be an abstract base class or an interface. According to LSP it shouldn’t make any difference what implementation of an abstraction you call from a client. Any concrete implementation of the abstraction should behave in a way that doesn’t break the client and doesn’t produce any unexpected and/or incorrect results. The client shouldn’t ever be concerned with the implementation details of an abstraction. It should be able to consume any concrete implementation “without batting an eye”.

Read more of this post

Filed under .NET, Design patterns, Design principles Tagged with , , , ,

Using Amazon DynamoDb for IP and co-ordinate based geo-location services part 8: creating the lng/lat coordinates source file for DynamoDb

May 3, 2015 Leave a comment

Introduction

In the previous post we successfully queried the limited IPv4 range table in DynamoDb and found the geoname ID that belongs to a single IP. We used 3 available integer properties in the table to narrow down the number of records that had to be scanned to reduce the query execution time and the risk for exceptions.

In this post we’ll start the same process for the lng/lat coordinate range. More specifically we’ll prepare the raw data file that can be uploaded into DynamoDb through S3. The process will be very similar to what we saw in this post where we created the IPv4 range source file. It is good idea to quickly re-scan that post to remind you of the process.

Read more of this post

Filed under Amazon, Java Tagged with , , , , ,

← Older posts

Newer posts →

Elliot Balynn's Blog

A directory of wonderful thoughts

Software Engineering

Web development

Disparate Opinions

Various tidbits

chsakell's Blog

WEB APPLICATION DEVELOPMENT TUTORIALS WITH OPEN-SOURCE PROJECTS

Once Upon a Camayoc

ARCHIVED: Bite-size insight on Cyber Security for the not too technical.