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C# – Use records as a shortcut for defining DTOs

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You can declare a record with a single line of code: Note: This feature was added in .NET 5 / C# 9. Records are basically classes (reference types) that work very well as simple data containers (i.e. DTOs). Here’s an example of using a record: This outputs the following: As shown, when you declare a … Read more

C# – Examples of using GroupBy() (Linq)

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Here’s an example of using the Linq GroupBy() method to group coders by language: This example outputs the following: GroupBy() produces groups that contain the grouping key (i.e. Language) and the list of objects in the group (i.e. the Coder objects). The GroupBy() syntax is complex because it supports many scenarios. You can select one … Read more

ASP.NET Core – How to receive a file in a web API request

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When the client posts a file in a multipart/form-data request, it’s loaded into an IFormFile object. This contains file information (such as the file name) and exposes the file content as a stream. This allows you to save the file content or process it however you want to. You can access the IFormFile object through … Read more

C# – How to read response headers with HttpClient

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When you send a request with HttpClient, it returns an HttpResponseMessage. You can read the response headers through the HttpResponseMessage.Headers property: This outputs the response headers: Raw response headers are really just key/value(s) pairs. When the response comes in, the headers are loaded into the Headers property (which is of type HttpResponseHeaders). This parses the … Read more

EF Core – Inheritance mapping

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There are two ways to do inheritance mapping in EF Core: Let’s say we have a database with employees. All employees have an id and a name. There are currently two types of employees: programmers and drivers. Programmers have a language (ex: C#), and drivers have a car (ex: Honda). We can model this with … Read more

C# – Use yield return to minimize memory usage

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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

ASP.NET Core – Getting query string values

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The ASP.NET Core framework automatically parses query strings (i.e. ?name=Dune&year=2021) into HttpContext.Request.Query and maps the query string values to parameters in the action method (if you’ve added them). You can get the mapped query string values by adding action parameters, like this: Or you can use HttpContext.Request.Query directly (which is useful in many scenarios): This … Read more

C# – Sending query strings with HttpClient

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Query strings start with ‘?’ and have one or more key-value pairs separated by ‘&’. All characters except a-z, A-Z, 0-9 have to be encoded, including Unicode characters. When you use HttpClient, it automatically encodes the URI for you (internally, it delegates this task to the Uri class). This means when you include a query … Read more

C# – Remove non-alphanumeric characters from a string

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The simplest way to remove non-alphanumeric characters from a string is to use regex: Note: Don’t pass in a null, otherwise you’ll get an exception. Regex is the simplest options for removing characters by “category” (as opposed to removing arbitrary lists of characters or removing characters by position). The downside is that regex is the … Read more

C# – Get all classes with a custom attribute

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To get all classes with a custom attribute, first get all types in the assembly, then use IsDefined(customAttributeType) to filter the types: This is looking for classes in the current assembly that have the [ApiController] attribute, such as this controller class: This is useful in several scenarios, such as when you want to log information … Read more

ASP.NET Core – Get posted form data in an API Controller

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To get posted form data in an API Controller (using the [ApiController] attribute) in ASP.NET Core, use parameters with the [FromForm] attribute. Now send a request with form data to this endpoint to see it work. The request would look like this: The form data is a string of key-value pairs (ex: location=United+States). The framework … Read more

C# – Convert a list to a dictionary

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The simplest way to convert a list to a dictionary is to use the Linq ToDictionary() method: This loops through the list and uses the key/element selector lambdas you passed in to build the dictionary. In this article, I’ll go into details about how to use ToDictionary() and show how to deal with duplicate keys. … Read more

C# – Unit testing code that does File IO

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If your code does File IO, such as reading text from a file, then it’s dependent on the file system. This is an external dependency. In order to make the unit tests fast and reliable, you can mock out the external dependencies. To mock out the file system dependency, you can wrap the File IO … Read more

C# – Select distinct objects based on a property with Linq

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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

C# – Using reflection to get properties

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You can get a list of a type’s properties using reflection, like this: Note: If you have an object, use movie.GetType().GetProperties() instead. This outputs the following: When you use GetProperties(), it returns a list of PropertyInfo objects. This gives you access the property’s definition (name, type, etc…) and allows you to get and modify its … Read more

C# – How to load assemblies at runtime using Microsoft Extensibility Framework (MEF)

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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

C# – Check if a string contains any substring from a list

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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

C# – Get types from assembly (reflection-only load)

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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

System.Text.Json – How to serialize non-public properties

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By default, System.Text.Json.JsonSerializer only serializes public properties. If you want to serialize non-public properties, you have two options: In this article, I’ll show examples of both approaches for handling non-public properties. Updated 2022-02-22 to explain the new JsonInclude attribute added in .NET 5. Write a custom JSON converter to serialize non-public properties When the built-in … Read more

WinForms – How to prompt the user for a file

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In a WinForms project, you can prompt the user to select a file by using the OpenFileDialog control: When you call ShowDialog(), it’ll prompt the user to select a file: When the user clicks Open, you’ll be able to get the file path they selected from the OpenFileDialog.FileName property. To use the OpenFileDialog control, drag … Read more

Collection was modified; enumeration operation may not execute

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If you try to add/remove items from a collection while it’s being looped over in a foreach loop (enumerated), then you’ll get the following exception: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.at System.Collections.Generic.List`1.Enumerator.MoveNext() This error can happen in two scenarios: The solution to this problem depends on which scenario you’re in. In this … Read more

C# – Remove a list of characters from a string

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When you want to remove a list of characters from a string, loop through the list and use string.Replace(): Note that string.Replace() returns a new string (because strings are immutable). Running this outputs the following: This is the fastest approach (in .NET 6+). Linq approach: Where() + ToArray() + new string() Another option for removing … Read more

C# – Get all loaded assemblies

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You can get all of the loaded assemblies with AppDomain.CurrentDomain.GetAssemblies(). Here’s an example of looping over all loaded assemblies and outputting their metadata: Note: This is outputting an interpolated string to the console. This outputs the following information: I’ll show more examples of how you can use the assembly information. Get custom assembly attributes Assembly … Read more

EF Core – Aggregate SELECT queries

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In this article, I’ll show how to use EF Core to aggregate data for the whole table, per group, and how to only include groups that meet a condition. I’ll show three different SQL aggregate functions – count, sum, and average. In each scenario, I’ll show the LINQ query, the SQL query it generated, and … Read more