Solve real coding problems
Each dictionary key maps to exactly one value. When you want multiple values per key, you can use a dictionary of lists. Here’s an example of creating a dictionary of lists, where each key maps to multiple ints: Notice that you can add to the dictionary like normal. The difference with a dictionary of lists … Read more
The simplest way to convert a dictionary to a list is by using the Linq ToList() method, like this: When used on a dictionary, ToList() returns a list of KeyValuePair objects. This example outputs the following: Dictionary keys to list If you want a list of the dictionary’s keys, use ToList() on Dictionary.Keys, like this: … Read more
Problem Dictionaries require keys to be unique. When you try to add a key/value to a dictionary and the key already exists, you get the following exception: System.ArgumentException: An item with the same key has already been added. This can happen when you use Dictionary.Add() or when you initialize a dictionary using the “curly brace” … Read more
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
There are four ways to add items to a list: I’ll show examples of all of these methods for adding to a list. Append items with List.Add() You can use List.Add() to append an item to the end of the list. Here’s an example: This outputs the list’s contents: Initialize a list with items You … Read more
You can convert a list of strings to a list of integers by using int.Parse() on all of the strings. There are two simple ways to do this: I’ll show examples of these using these methods and then explain how to handle parsing exceptions. Option 1 – Use List.ConvertAll() Here’s an example of how to … Read more
Here’s an example of how to initialize a list of named tuples: This creates a list of named value tuples (ValueTuple<string, int>) using list initializer syntax and then loops through the tuples. I suggest always using named value tuples (not System.Tuple). This outputs the following: I’ll now show how to add to the list of … Read more
There are two ways to receive CSV data in a web API: In this article, I’ll show examples of both of these approaches. I’ll be using the CsvHelper library to parse CSV data into model objects and then do model validation. Note: To use CsvHelper, install the CsvHelper package (Install-Package CsvHelper). Or use whichever parser … 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
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
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
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
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 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
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
In this article I’ll show how to use the SqlDataReader ADO.NET class in two scenarios involving multiple result sets: I have a StreamingService database that has Movies, Shows, and Episodes tables (linked to the shows). First I’ll show the model classes I’m mapping the data into. Then I’ll show the two scenarios where I’m using … 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’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
I want to log method calls, including their parameter names and values, and what called the method. I want to minimize the amount of coding involved. For example: What options are available? In this article I’ll explain how to use the simple built-in approach. 1 – Create LogMethodCall() utility method The System.Diagnostics.StackFrame class gives us … Read more
The Large Class code smells refers to a class that has too many responsibilities. It’s doing too much. Ideally a class should only have one responsibility (Single Responsibility Principle). Code Smell: Large Class Definition: A class has too many responsibilities. Solution: Large Class code smell example Here’s an example of the Large Class code smell … 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
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
I often need to be able to run multiple threads and update the UI based on the results. For example, I may need to execute GET requests to 10 different endpoints concurrently, and then report their results in a datagrid as they come back. The problem is you can’t just update the UI from any … Read more