Скачать или смотреть How to Select a Collection Based on Condition in EF Core

Learn how to effectively select collections based on conditions in EF Core by splitting queries for better performance and clarity.
---
This video is based on the question https://stackoverflow.com/q/67211296/ asked by the user 'Hubert Mijalski' ( https://stackoverflow.com/u/7314120/ ) and on the answer https://stackoverflow.com/a/67211576/ provided by the user 'StPaulis' ( https://stackoverflow.com/u/6442841/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to select a collection based on condition in EF Core?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Select a Collection Based on Condition in EF Core

Introduction

Entity Framework Core (EF Core) is a powerful tool for data access in .NET applications. As developers, we often need to work with collections and make decisions based on certain conditions. One common challenge arises when you have an object that contains multiple lists, and you need to select one of those lists based on a conditional statement. Let's explore how to achieve this efficiently.

The Problem

In this scenario, we have an object representing a Person, which includes two lists of employees: WorkerList1 and WorkerList2. Depending on whether the person is a manager (IsManager), we want to select one of the two lists. Here’s what the code for the initial attempt looks like:

[[See Video to Reveal this Text or Code Snippet]]

Both lists contain objects of the same type, but trying to union or concatenate the lists leads to errors due to translation issues in EF Core. Attempts to use an intermediate query for mapping the objects also fail to translate.

The Solution

Splitting Queries for Better Control

Instead of trying to select the collection in one go, a more efficient approach is to split your queries. This will allow you to handle each case independently, ensuring you can apply any necessary transformations or selections without running into translation issues.

Step-by-step Solution

Create separate queries for managers and non-managers. This will help you isolate the logic and avoid complications that arise when you attempt to combine both lists in a single query.

[[See Video to Reveal this Text or Code Snippet]]

Map the results independently. You can then apply your transformations on the results of each query, allowing you to create your desired outputs without translation failures.

[[See Video to Reveal this Text or Code Snippet]]

Combine the results if needed. If you need a single collection from both lists, consider using Concat to merge the results after transformation.

[[See Video to Reveal this Text or Code Snippet]]

Benefits of This Approach

Improved Clarity: Each query addresses a specific condition, making the code easier to read and maintain.

Effective Error Handling: By isolating the conditions, you can more easily handle potential errors or exceptions.

Better Performance: Executing separate queries can sometimes yield performance benefits, especially with larger datasets.

Conclusion

Selecting collections based on conditions in EF Core can seem daunting when faced with translation issues. However, by splitting your queries into clear and manageable components, you can efficiently handle the logic with clarity and performance in mind. Embrace this approach, and you’ll enhance both your code quality and your development process.

Should you encounter further questions or need examples of specific use cases, feel free to reach out. Happy coding!