Скачать или смотреть Combining Two Rows into One DTO in Entity Framework Core

Learn how to efficiently retrieve multiple rows as a single DTO in `Entity Framework Core`, making your data comparison tasks easier.
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This video is based on the question https://stackoverflow.com/q/68750001/ asked by the user 'Lisum' ( https://stackoverflow.com/u/8156937/ ) and on the answer https://stackoverflow.com/a/68750063/ provided by the user 'Svyatoslav Danyliv' ( https://stackoverflow.com/u/10646316/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Combining Two Rows into One DTO in Entity Framework Core

When working with databases, particularly in Entity Framework Core, you may often find the need to retrieve multiple rows from a table and present them in a more concise format. This is especially useful in situations where you need to compare different versions of a document or any other entity. In this post, we'll explore how to select rows from a single table into a single Data Transfer Object (DTO) with multiple properties.

The Problem

Suppose you have a Document model defined as follows:

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

You are tasked with writing a method that compares two versions of a document. Specifically, you need to fetch the texts of these two documents based on their IDs and present them in a way that clearly distinguishes which text belongs to which version. Your current approach involves constructing a dictionary to achieve this, which can feel cumbersome and less intuitive.

Current Method

Your current implementation looks like this:

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

Afterward, you might access the texts like so:

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

While this works, it can quickly turn into a maintenance nightmare as your project grows.

The Solution: Using LINQ to Select into DTO

Instead of using a dictionary, you could utilize the powerful features of LINQ in Entity Framework Core to select both documents directly into a single anonymous object DTO. Here’s how you can do this more elegantly:

The Revised Query

To retrieve the two versions of your document text within a single DTO, you can use the following query structure using LINQ:

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

Breaking Down the Code

From Clause: The first part of your query selects the initial document based on the initialId.

Where Condition: This ensures you are retrieving the correct document using an equality check.

Select Clause: This allows you to define a new anonymous object with properties for the initial and final texts.

Query Execution: Finally, FirstOrDefaultAsync() retrieves the combined result.

This approach is not only cleaner but allows you to directly access the texts without the extra overhead of key-value pairs.

Accessing the Result

After executing this query, you can easily retrieve the texts like this:

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

Conclusion

By transforming your original query into one that uses LINQ, you achieve a more streamlined approach to fetching and comparing document versions. This method not only improves readability but also maintainability.

Using Entity Framework Core effectively allows you to structure your data access in a more natural way, making your application more efficient and easier to understand.

Feel free to experiment with this method and see how it can simplify your workflows in other areas of your application as well!