Solve real coding problems
The simplest (and most efficient) way to remove duplicates from a list is by iterating, keeping track of items you’ve seen with a HashSet, and discarding items you’ve already seen. I’ll show four ways to implement this O(n) algorithm. At the end, I’ll explain a few inefficient approaches to avoid. Remove duplicates with ToHashSet() and … Read more
Let’s say you want to parse a comma-separated string into a list of integers. For example, you have “1,2,3” and you want to parse it into [1,2,3]. This is different from parsing CSV with rows of comma-separated values. This is more straightforward. You can use string.Split(“,”) to get the individual string values and then convert … Read more
You can use the Validator utility class to do manual attribute-based validation on any object, in any project type (as opposed to doing automatic model validation in ASP.NET). To do this, add model validation attributes to your class properties, then create an object and populate it (aka binding), and finally execute manual validation with the … Read more
Mapping classes to WinForm controls manually is probably the most tedious thing you can do in coding. In order to minimize this coding effort, you can bind your controls to an object data source. In this article, I’ll show how to do this in a WinForms App (.NET Core+) project. First, I’ll show step-by-step how … Read more
When you have a collection of elements that you’re continuing to add to, and need to keep the objects in sorted order at all times, you can use SortedSet. Internally, it uses a tree data structure to keep elements in sorted order (O(log n) insertion). This is far more efficient than repeatedly sorting a list … Read more
Normally when you’re working with JSON, you deserialize it to a target type and get back an initialized and fully populated object. How about if you need to initialize an object yourself, and then populate it with JSON later? For example, let’s say you want to load the following JSON array into a case-insensitive HashSet: … Read more
The simplest way to implement GetHashCode() is to use the built-in System.HashCode.Combine() method and pick the properties you want to include. Let it do the work for you. Furthermore, the simplest way to implement Equals() is to use the is operator and compare all the properties. Here’s an example: Note: Use (Title, Year).GetHashCode() in versions … Read more
Let’s say you want to search for specific characters in a large text file and return a list of context objects to the calling code for further processing (such as showing the results in the UI). One way to do that is to build the entire list at once and return it. If you don’t … Read more
There are three ways to select distinct objects based on a property using Linq methods: These select one movie per year: The simplest option is using GroupBy() because it doesn’t require any additional code. Distinct() is faster but it’s more complicated. DistinctBy() is the fastest and simplest, but requires the most code (it requires .NET … Read more
I was reading about logging in ASP.NET when I came across this statement about logging to the database: When logging to SQL Server, don’t do so directly. Instead, add log messages to an in-memory queue and have a background worker dequeue and insert data to SQL Server. Paraphrased from Microsoft – No asynchronous logger methods … Read more
Here’s how you can use Enum as a generic constraint: Note: Microsoft added this feature in C# 7.3. Whenever you have a generic method, it’s a good idea to use generic type constraints. Without constraints, you would have to implement type checking in the generic method and throw exceptions if an invalid type was used. … Read more
Let’s say you have a list of HTTP status codes that you read in when the service starts up (perhaps from appsettings.json or from the database). Whenever you send an HTTP request, you want to check if the returned status code is in this list of status code. To make things more efficient, you want … Read more
In this article, I’ll explain how to solve the Two Strings algorithm problem on HackerRank. Problem statement: Given two strings, determine if they have a substring in common. The strings can have up to 100k characters. Example: Given “hello world” and “world”, do they have a substring in common? Yes, they many substrings in common. … Read more
Most of the time System.Text.Json will get you want you want. You can pass in options to control JSON serialization and deserialization to a certain extent. But sometimes you’ll run into scenarios where you need to customize how it handles a specific type. This is where JsonConverter comes in. You can customize serialization / deserialization … Read more
In this article, I’ll explain four set operations – intersection, union, difference, and symmetric difference – and how to perform these operations using Linq methods (such as Intersect()). These methods work on any type that implements IEnumerable – such as lists, arrays, and sets. Set intersection with Intersect() The intersection of set A {1,2} and … Read more
You can use exception filtering to conditionally catch exceptions, like this: Note: This feature was added in C# 6. Any SqlException that doesn’t meet the condition specified in the when clause will not be caught. Previously, without exception filtering, you’d have to handle that scenario in the catch block and rethrow, like this: Exception filtering … Read more
A default constructor is a constructor that doesn’t have parameters. Therefore, to check if a type has a default constructor, you can use reflection to loop through the constructors and see if there are any with no parameters, like this: In this article I’ll show an example of loading types that implement a specific interface … Read more
Let’s say you have the following async method you want to test: Here’s how to unit test this: This is awaiting the method you’re testing. To await it, you must make the unit test method return async Task. This example is a bit simplistic. In the real world when you are working with async methods, … Read more
In this article, I’ll explain how to implement the plugin pattern. This approach uses a generic plugin loader that solves many real world problems when loading plugins in .NET. Besides being generic, this plugin loader also solves the following real world problems when working with plugins: If you find that this generic plugin loader doesn’t … Read more
I’ll show how to parse comma-separated integer values from app.config and load them into a HashSet for efficient lookups. First, take a look at the setting (retryStatusCodes) in app.config: To load and parse this setting from app.config, do the following: The following code shows how to do this: Note: You have to add a reference … Read more