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C# – How to use JsonNode to read, write, and modify JSON

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When you don’t want to create classes for JSON (de)serialization, one option is to use JsonNode. This allows you work with JSON as a mutable DOM that consists of JsonNode objects (JsonObject, JsonArray, JsonValue). You can use it to read, write, and modify JSON. Here’s an example. Let’s say you have the following JSON that … Read more

C# – TimeZoneInfo with current UTC offset

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TimeZoneInfo always shows the base UTC offset. This can be confusing because the UTC offset can change based on the date (due to daylight savings rules). Here’s an example showing DateTimeOffset and TimeZoneInfo with different offsets: You can get a date’s UTC offset from DateTimeOffset and combine it with TimeZoneInfo.DisplayName. This approach is implemented in … Read more

C# – How to use TimeZoneInfo

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Time zones are complicated and their rules can change, so it makes sense to use a library when you’re dealing with them. One option in .NET is to use the built-in TimeZoneInfo class. Here’s an example of using TimeZoneInfo to get the local system’s time zone: This outputs: Note: The display name always show the … Read more

C# – Get key with the max value in a dictionary

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The simplest way to get the key with the max value in a dictionary is to use the Linq MaxBy() method (added in .NET 6). This returns the key/value pair with the max value. Here’s an example: Note: All examples shown initialize the dictionary with a small number of key/value pairs for readability. This outputs … Read more

WinForms – Loop through a form’s controls

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Forms also have a collection of controls (Controls property) that you can loop through. This is useful for when you want to do something to multiple controls and don’t want to have to manually type out code to deal with individual controls. Here’s an example of looping through a form’s top-level controls: Note: In the … Read more

C# – Check if a property is an enum with reflection

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When you’re using reflection to look at a type’s properties, you can use PropertyInfo.PropertyType.IsEnum to check if the property is an enum. This is helpful when you want to be able to safely call an Enum API method (such as Enum.Parse()) on the reflected type, thus preventing an exception – ArgumentException: Type provided must be … Read more

ASP.NET Core – How to get request headers

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There are two ways to get request headers: When a request comes in, the framework loads request headers into the Request.Headers dictionary. You can use this just like any other dictionary. Here’s an example of using TryGetValue() to check if a request header exists and get its value: Note: To just check if a header … Read more

C# – How to read problem details JSON with HttpClient

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Problem details (RFC7807) is a standardized error response format that has a Content-Type of application/problem+json, an error response code (i.e. 400 – Bad Request), and has a response body that looks like this: This can be extended to include any number of properties. The example shown above comes from the default way ASP.NET Core returns … Read more

C# – How to unit test a model validation attribute

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You can unit test a validation attribute by creating an instance of it and then testing the two methods: In this article, I’ll show examples of unit testing these methods in a custom validation attribute and in a built-in validation attribute (i.e. [Range]). Unit testing a custom validation attribute Consider the following custom validation attribute … Read more

ASP.NET Core – Create a custom model validation attribute

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There are many built-in model validation attributes available – such as [Required] and [Range] – which you can use to handle most validation scenarios. When these aren’t sufficient, you can create a custom validation attribute with your own validation logic. I’ll show an example of how to do that. 1 – Subclass ValidationAttribute and implement … Read more

C# – How to read the Description attribute

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You can use the Description attribute to describe types and type members (properties, methods). One of the most common use cases is providing a user-friendly string for enum values. Here’s an example of using the Description attribute with an enum: To read the Description attribute, use reflection and do the following steps: This can be … Read more

C# – How to use JsonExtensionData

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Use the JsonExtensionData attribute (in System.Text.Json) to deserialize properties that aren’t part of the class. Without this, JSON fields that don’t match a property are simply ignored and the returned object will have null properties. Here’s an example of adding this attribute to a dictionary property: Now when you deserialize JSON to this Person class, … Read more

C# – How to use JsonConverterAttribute

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You can use JsonConverterAttribute (from System.Text.Json) to apply a specific JsonConverter to a property. Apply this attribute on a property and specify the JsonConverter type to use, like this: In this example, it’s applying ExpirationDateConverter (a custom JSON converter) to handle the ExpirationDate. For reference, here’s ExpirationDateConverter’s definition: Now serialize the object to JSON: Here’s … Read more

C# – Using top-level statements

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The top-level statements feature makes the Main() method implicit. This feature was added in C# 9 (.NET 5) with the purpose of decluttering a project’s entry point. Here’s what a console app looks like using a top-level statement: The compiler generates the Main() method implicitly from the top-level statements. The code above is functionally equivalent … Read more

C# – Map query results to multiple objects with Dapper

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When you’re querying joined tables, you can map each row to multiple objects by using the multi mapping feature in Dapper. To multi map, you have to provide Dapper with the following: In this article, I’ll show examples of multi mapping. Note: If you don’t specify the split column, it’ll use the default of “Id”. … Read more

C# – Round up to the nearest 30 minutes

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Here’s how to round a DateTime up to the nearest 30 minutes: When the time is 3:38 pm, it rounds to 4:00 pm. When it’s 5:03 pm, it rounds to 5:30 pm. When it’s exactly 2:00 pm, it’ll round up to 2:30 pm (note: see the What if you’re at the start of a 30 … Read more

C# – How to send a file with HttpClient

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In order to send a file in a request with HttpClient, add the file into a MultipartFormDataContent object, and send this object as the request content. Here’s an example: This sends the following multipart/form-data POST request: In this article, I’ll explain a few details about MultipartFormDataContent, and show a few other file-sending scenarios. MultipartFormDataContent Add() … 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

C# – Save a list of strings to a file

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The simplest way to save a list of strings to a file is to use File.WriteAllLines(). This creates (or overwrites) the file and writes each string on a new line. The resulting file looks like this: Note: Showing non-printable newline characters \r\n for clarity. Specifying the separator character What if you want to separate each … 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# – 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

C# – Trim a UTF-8 string to the specified number of bytes

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Here’s the simplest way to efficiently trim a UTF-8 string to the specified number of bytes: A UTF-8 string can have a mix of characters between 1 to 4 bytes. When you only take part of the byte array, you may end up cutting multi-byte chars in half, which then get replaced with the replacement … 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

Moq – Verifying parameters passed to a mocked method

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When you need to verify that the code under test called a method with the expected parameters, you can mock the method with Moq and use Verify() + It.Is<T>() to check the parameters passed in. Verify() asserts that the method call happened as expected with the specified parameters. Here’s an example. This is verifying that … Read more