How Does EF Core's Filtered Include Optimize Queries by Filtering Related Entities?

EF Core 5's Filtered Include: Streamlining Related Entity Filtering

Entity Framework Core (EF Core) frequently requires filtering data while including related entities. Prior to EF Core 5, this often involved cumbersome workarounds. The introduction of "Filtered Include" significantly simplifies this process.

Understanding Filtered Include Functionality

Filtered Include allows filtering included entities based on properties of their navigation properties. Supported operations include Where, OrderBy/ThenBy (ascending/descending), Skip, and Take.

Consider this example model:

<code>public class Blog
{
    public int BlogId { get; set; }
    public ICollection<Post> Posts { get; set; }
}

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public int AuthorId { get; set; }
    public Author Author { get; set; }
}

public class Author
{
    public int AuthorId { get; set; }
    public string Name { get; set; }
}</code>

To include posts filtered by author name:

<code>using (var context = new BloggingContext())
{
    var blogs = context.Blogs
        .Include(blog => blog.Posts.Where(post => post.Author.Name == "Alexander"))
        .ToList();
}</code>

Key Considerations

• Relationship fixup might include extra entities.
• Filter expressions should be self-contained predicates.
• Filtered Include doesn't impact overall query filtering.
• Projections generally ignore Includes (including filtered ones), with exceptions when projecting the included entity itself.

Benefits of Using Filtered Include

• Simplified query optimization.
• Improved performance through reduced data retrieval.
• Enhanced query control with related entity filtering.

In Summary

Filtered Include in EF Core 5 provides a powerful and efficient way to manage related entity filtering. This feature optimizes queries, improves performance, and offers more precise control over data retrieval in your EF Core applications.

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