SOLID principles in .NET revisited part 8: clean-up

May 18, 2015 2 Comments

Introduction

In the previous post we covered letter ‘D’, i.e. the Dependency Inversion Principle among the SOLID principles.
A class can have a number of dependencies in order to perform its functions properly. Applying DIP will open an entry point for the clients to supply their own implementations for those dependencies when they call upon that class. The class in turn can remove all responsibility of creating concrete implementations for its abstract dependencies. The result will be loosely coupled code where a class won’t be tightly coupled to concrete services.

In this post we’ll only clean up a couple of remaining issues in the code.

Remove “virtual”

In the post on OCP we mentioned that the “virtual” keyword provided an extensibility point for a class. However, since then we know that abstractions provide a much better alternative. Hence we don’t have to make our methods virtual any more:

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Using Amazon DynamoDb for IP and co-ordinate based geo-location services part 12: querying the geolocation range to DynamoDb

May 17, 2015 Leave a comment

Introduction

In the previous post we created the DynamoDb source file with a reduced set of geolocations from the full MaxMind data source. We saw how we could reuse the same process as before in the case of the IP and coordinate range tables.

In this final post of this series we’ll close the loop by actually extracting and geographic properties of a geoname ID. After all you’d like to know whether a visitor come from New York other than “geoname ID 3452334”.

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Using Amazon DynamoDb for IP and co-ordinate based geo-location services part 11: uploading the geolocation range to DynamoDb

May 16, 2015 Leave a comment

Introduction

In the previous post we successfully queried the coordinate range database in DynamoDb. We used the query endpoints that are built into the AWS geo-location library to find the data records within the radius around a centre point.

Where are we now?

We’ve got quite far with our project. We have the ability to query an IPv4 and coordinate range table in DynamoDb. We can extract a geoname ID that belongs to either an IP or a latitude-longitude pair. The next step is to dress up those IDs with real location data such as “Stockholm” or “Tehran”.

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How to declare natural ordering by overriding the comparison operators in C# .NET

May 15, 2015 1 Comment

In this post we saw one way to declare natural ordering for a custom class by implementing the generic IComparable of T interface. In this post we’ll look at how to achieve the same by overriding the 4 comparison operators: 

<
>
<=
>=

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SOLID principles in .NET revisited part 7: the Dependency Inversion Principle

May 14, 2015 5 Comments

Introduction

In the previous post we saw the definition of the Interface Segregation Principle. We applied it to a problematic case where a class could not fully implement the IAuthorizationService interface. We then broke up the interface into two parts so that they became more specialised. A consequence of ISP is often a large number of small, very specialised interfaces of 1 or maybe 2 methods. Large, monolithic interfaces are to be avoided as it will be more difficult to find concrete classes that can meaningfully implement all interface methods.

We’ve reached the last letter in the SOLID acronym, i.e. ‘D’ which stands for the Dependency Inversion Principle.

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Combinable enumerations in C# .NET: numeric values of large enums

May 13, 2015 2 Comments

In this post we saw how to build an enumeration that can be combined using the bitwise OR, i.e. | operator:

var frontEndProgrammer = SoftwarePositions.Programmer | SoftwarePositions.FrontEnd;

We saw that enumeration values must be set in powers of two:

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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.

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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.

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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.

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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.

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