Скачать или смотреть How to Parameterize a LINQ Select Distinct Query in C#

Discover how to effectively parameterize your LINQ queries using C# for better code reusability and maintainability.
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This video is based on the question https://stackoverflow.com/q/64707111/ asked by the user 'pamianthe' ( https://stackoverflow.com/u/14586985/ ) and on the answer https://stackoverflow.com/a/64709434/ provided by the user 'Jeremy Lakeman' ( https://stackoverflow.com/u/4139809/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Parameterize a LINQ Select Distinct Query in C#

Working with LINQ (Language-Integrated Query) can be exhilarating, especially when you need to extract distinct values from your data collections. However, parameterizing a Select with Distinct query can sometimes pose challenges. Let's delve into this common problem and provide a practical solution that will enhance your code's reusability and maintainability.

The Problem: Parameterizing Select Distinct Queries

Imagine you’re tasked with retrieving a distinct list of customer codes and family names from an ObservableCollection<Model>. This typically involves using the LINQ methods Select, Distinct, and OrderBy, as illustrated in the provided code snippet:

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While this works perfectly for its intended function, you seek to convert your approach into a more flexible method that allows for passing parameters for the Select and OrderBy clauses.

The Initial Attempt: Challenges Faced

Upon your first attempt to create a parameterized method getDistinct, you found that while it worked with a single property, passing a second property resulted in errors. Here’s a snippet of what you tried:

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This method correctly executed when called with a simple property but failed when trying to pass multiple properties. The error indicated that the method wasn’t able to recognize the OrderBy extension method on the generated distinct elements.

The Solution: Refactoring the Method

To address these issues and effectively parameterize the method, we can adjust the way distinct values are selected and how they are sorted. Below is an updated version of your getDistinct method, which constructs new Model objects directly:

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This method takes two parameters: one for selecting distinct items and another for sorting. The Distinct() method utilizes the overridden equality comparisons in the Model class to ensure the uniqueness of the returned items.

Example of Invoking the Method:

Now you can call this parameterized method like so:

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Conclusion: Embracing Flexibility in Your LINQ Queries

By restructuring your method as shown above, you’ll harness the power of LINQ more efficiently—allowing for a more versatile querying capability while maintaining clean and manageable code. This method not only limits redundancy but also provides easy adjustments for future needs.

With just a few modifications, you can seamlessly retrieve distinct values with a variety of properties, strengthening your C# programming skills.

Should you run into any other challenges or have questions regarding LINQ or data manipulation in C# , feel free to reach out for assistance. Happy coding!