Solve real coding problems
Articles about coding with C# in .NET projects.
When you’re using Moq to set up a mocked method, you can use Callback() to capture the parameters passed into the mocked method: There are two main use cases for capturing parameters in a test: In this article, I’ll show examples of using Callback() in those two scenarios, and then I’ll explain some problems to … Read more
Problem Optional parameters aren’t optional when you’re using Moq. When you’re setting up or verifying a method call on a mock object, and the method has an optional parameter that you didn’t specify a value for, you’ll get the following compiler error: Error CS0854 – An expression tree may not contain a call or invocation … Read more
In this article, I’ll explain how to solve the Mark and Toys algorithm problem on HackerRank. Problem statement: Given a fixed budget and a list of item prices. What is the max number of items you can purchase? You can only buy each item once. Note: This is the Mark and Toys problem from HackerRank. … Read more
Use the XElement class (from the Linq-to-Xml API) to search for XML elements by name. There are two main methods you can use to do this: These return the matching elements as an IEnumerable<XElement>. You can then use Linq methods (or a foreach loop) to do whatever you want with these elements (such as outputting … Read more
In an electrical system, a circuit breaker detects electrical problems and opens the circuit, which blocks electricity from flowing. To get electricity flowing again, you have to close the circuit. The same approach can be implemented in software when you’re sending requests to an external service. This is especially important when you’re sending lots of … Read more
You have to overwrite the appsettings.json file to be able to update values programmatically. You have to deal with the whole file, not individual parts of it. The process can be summarized in the following steps: There are two options for deserialization. You can either 1) Deserialize appsettings.json into a dynamic object or 2) Load … Read more
There are two global exception events available in all .NET applications: You wire up these event handlers in Main() (before anything else has executed), like this: Note: If you’re using top-level statements, put these statements at the top of the ‘entry point’ file. This outputs the following before crashing: Notice the FirstChanceException event fired first. … Read more
You can use Microsoft Extensibility Framework (MEF) to load assemblies at runtime. This is an alternative to implementing dynamic assembly loading with a more manual approach (like using AssemblyLoadContext). Here’s an example of using MEF to load an instance of IMessageProcessorPlugin from some assembly located in the C:\Plugins directory: MEF looks for exported types in … Read more
There are many different scenarios where you might want to check a string against a list of substrings. Perhaps you’re dealing with messy exception handling and have to compare the exception message against a list of known error messages to determine if the error is transient or not. When you need to check a string … Read more
Whenever you’re dealing with code that can run into transient errors, it’s a good idea to implement retries. Transient errors, by definition, are temporary and subsequent attempts should succeed. When you retry with a delay, it means you think the the transient error will go away by itself after a short period of time. When … Read more
EF Core has built-in retry functionality. To use it, you can call options.EnableRetryOnFailure(), like this: The retry logic is contained in execution strategy classes. The above code is using the default execution strategy class (SqlServerRetryingExecutionStrategy). When you execute a query, it goes through the execution strategy class. It executes the query and checks for transient … Read more
There’s two ways to unit test code that writes to the console (Console.WriteLine() / Console.Write()): In this article, I’ll show how to do both options. Option 1 – Capture the output with Console.SetOut() Let’s say you want to unit test the following code that outputs to the console with Console.WriteLine(): You can unit test this … Read more
You can get all types from an assembly by doing a reflection-only load. This allows you to read type info from metadata without running the typical errors associated with fully loading an assembly. The way to do a reflection-only load is different in .NET Framework and .NET Core. I’ll show examples of how to do … Read more
You can use the is operator to check if an object is a certain type. Here’s an example: You can also use the is operator to declare a variable of the target type, like this: Note: The employee object is only available in the if block, but IntelliSense shows it out of its scope. If … Read more
Padding a 2D array on all sides means adding new rows on the top and bottom, new columns on the left and right, and then copying the original elements to the center of the padded array. It looks like this: There are two approaches for copying the elements. You can either copy individual items in … Read more
Table-valued parameters (TVP) allow you to send multiple rows of data as a parameter into SQL queries. This is useful for SELECTs and INSERTs. In this article, I’ll show how to create a TVP in SQL Server and then use it in queries with Dapper. 1 – Create the TVP in SQL Server To be … 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
Problem You’ve configured user secrets properly, but the framework will not swap in the secret value at runtime. It appears to not be loading secrets.json at all. Check if you’re using GenerateAssemblyInfo=false in your .csproj file. When you add a user secrets file, it generates a user secrets guid and puts it in your .csproj … Read more
When a background service throws an unhandled exception in ExecuteAsync(), you have two options: You can change the behavior if the default isn’t what you want (notice the default behavior changed in .NET 6). In .NET 6+, you can configure the behavior in the initialization code. Here’s an example of making it ignore crashed background … Read more
The options pattern is an indirect way to dependency inject settings into a registered service. If you’re using code that implements the options pattern, then you’re required to supply an IOptions<T> object. For example, let’s say you’re using the MovieService class and it has the following constructor: This requires you to supply the IOptions<MovieSettings> parameter. … Read more
When you try to call BuildServiceProvider(), you get the following warning: Warning ASP0000 Calling ‘BuildServiceProvider’ from application code results in an additional copy of singleton services being created. Consider alternatives such as dependency injecting services as parameters to ‘Configure’. There are two scenarios where you may be calling BuildServiceProvider() because you want to resolve services … Read more
Let’s say you have a hosted BackgroundService called DatabaseLoggerService. It runs in the background and logs messages to the database. It has the following definition: You want your controllers to use this for logging. In other words, you want them to depend on ILoggerService, not the concrete DatabaseLoggerService class. First, constructor inject ILoggerService into your … Read more
In a consumer/producer scenario, there are many reasons why you might want the consumer to read a batch of items. Maybe you’re bulk inserting into the database, or sending a payload with HttpClient. Sending lots of individual items over the network can be costly, and waiting for a full batch of items before sending is … Read more
If you try to set a list control’s DataSource to a type it can’t handle, then you’ll get the following exception: System.ArgumentException: Complex DataBinding accepts as a data source either an IList or an IListSource. (Parameter ‘value’)at System.Windows.Forms.ListControl.set_DataSource(Object value) Note: This applies to all controls that subclass ListControl, such as ComboBox and ListBox. This is … Read more
When you want to use NLog in ASP.NET, the first step is to install and configure NLog. Then you can either use it directly or fully integrate it and ASP.NET. Use NLog directly if you prefer to have static ILogger properties, instead of using dependency injection. The downside of this approach is that you’ll have … Read more