Solve real coding problems
When you’ve created tables that are related, you’ll often need to get data from both tables at once, or filter records from one table based on values in another table. In this article, I’ll show examples of executing queries like this where more than one table is involved. You can do most queries using LINQ. … Read more
In this article, I’ll show examples of how to execute basic SELECT queries when using EF Core. You can execute queries using LINQ or by writing raw SQL. I’ll use SQL Profiler to show the queries generated by LINQ. Note: I’ll be using .AsNoTracking().ToListAsync() in all cases. You’ll need to decide if that’s the right … Read more
In this article, I’ll show how to add a foreign key using EF Core. Then I’ll show how foreign keys affect inserts and deletes. How to add a foreign key A Show has one or more Episodes. In this section, I’ll show how to link these two tables together to enforce the 1-to-many relationship. In … Read more
Normally the items in a CheckedListBox are hardcoded or added programmatically (from an enum or from binding a data source). But sometimes you may want to allow the user to add and remove items from a CheckedListItem. In this article I’ll show how to add items and remove them. I’ll be working with text, and … Read more
When you have a public method that isn’t null checking its parameters, then you’ll get the CA1062 code analysis warning. This is part of the Nullable Reference Types feature. For example, the following code isn’t null checking the movieRepository parameter: This results in the CA1062 code analysis warning: CA1062 In externally visible method ‘void StreamingService.LogMovies(MovieRepository … 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
When you need to insert multiple rows into the database, consider doing a Bulk Insert instead of inserting one row at a time. Bulk Insertions are up to 20x faster than executing SQL Insert repeatedly. The simplest way to do a SQL Bulk Insert is by using the built-in SqlBulkCopy (from System.Data.SqlClient) with a DataTable. … 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
Given an IP range as a starting IP address and an ending IP address (as strings, like from user input or a config file), you can check if the IP range is valid by doing the following steps: Here’s an example. Let’s say you’re given starting IP “192.168.0.1” and ending “192.168.0.11”. The following table shows … Read more
When you merge two dictionaries, you can either merge them in-place, or create a new dictionary and copy the values over to it. The following extension method does an in-place merge of two dictionaries. It loops through items in the right dictionary, adding them to the left dictionary. When duplicate keys exist, it’s keeping the … Read more
To sort a list, except for the first element, you need to: This can be accomplished in a single line using Linq methods: I’ll show a full example and explain how this works. Example – sorting a list of people Let’s say we have a list of people, such as the following: Here’s how to … Read more
Before .NET 5, the built-in JSON serializer (System.Text.Json) couldn’t handle serializing a dictionary unless it had a string key. Here’s an example running in .NET Core 3.1 to show the problem. This is initializing a dictionary with values and then attempting to serialize it. This results in exception: System.NotSupportedException: The collection type ‘System.Collections.Generic.Dictionary`2[System.Int32,System.String]’ is not … Read more
The simplest way to check if a directory is empty is by calling Directory.EnumerateFileSystemEntries(). If this doesn’t return anything, then the directory doesn’t have any files or subdirectories (folders), which means it’s empty. Here’s an example: Another situation to consider is when a directory has no files but might have empty subdirectories (folders). You can … Read more
The Channel class (from System.Threading.Channels) is a non-blocking async queue. It implements the producer-consumer pattern, which has two parts: Compare this with using BlockingCollection, which is a blocking concurrent queue. In this article, I’ll show how to use a Channel. 1 – Create the Channel The first step is to create the Channel object. Here’s … Read more
Problem You are trying to use a lambda expression on a dynamic object and get the following compiler error: Cannot use a lambda expression as an argument to a dynamically dispatched operation without first casting it to a delegate or expression tree type. As an example, the following code causes this error: Solution Cast the … 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
You can use reflection to get all classes in the current assembly that implement a specific interface. Here’s how: To create instances of these types, loop through them and use Activator.CreateInstance(), like so: Example – Auto-wire a command routing table Let’s say we want to build a command routing table. We have commands and want … 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
If you want to deserialize JSON without having to create a bunch of classes, you can either deserialize to a dictionary or deserialize to a dynamic object with Newtonsoft.Json. Here’s an example. Let’s say you want to deserialize the following JSON: To deserialize this to a dynamic object with Newtonsoft, use JsonConvert.DeserializeObject<dynamic>: This outputs the … Read more
If you’re working on a Windows Forms project and need to know which forms are open, use: This gives you an IEnumerable collection of form objects that are currently open. You can lookup a form by name, by type, or loop through the list. Example scenarios There are many scenarios where you’d want to know … Read more
In regex, capturing groups give you a way to save text and refer to it later. Capturing groups can be named, and referred to by their name. When they aren’t named, you refer to them by their index number. In this article, I’ll show how to use named capturing groups by solving the problem of … Read more
In this article, I’ll explain how to solve the Sock Merchant algorithm problem on HackerRank. Problem statement: You’re given an integer array and need to count the number of pairs of matching integers. The integers will be between 1 and 100. For example, [3,1,3] has one matching pair (the 3s match). Approach First, we know … Read more
A CheckedListBox is a list control with multiple checkboxes. This allows the user to check multiple boxes at once. You can also programmatically check items in the CheckedListBox and remove them. How can I can get all the values they selected? By looping through the CheckedListBox.CheckedItems collection. See the UI and Code examples below. UI … Read more
Imagine you’re in the middle of Millennium Park in Chicago. You want some coffee, but want a good deal on it. You open an app and see the nearest coffee shops offering deals to anyone with this app. How did this app know the distance from you to the coffee shops? This article will show … Read more
One day I decided to challenge myself by trying to implement multithreaded quicksort. I wanted to see how it would compare to the built-in Array.Sort() method. I came up with two algorithms that were 2-4x faster than Array.Sort(): After continuing to tinker, in attempts to further optimize, I came across the AsParallel().OrderBy() method (PLINQ). After … Read more