How Can I Filter Included Navigation Properties in Entity Framework Core?

Filtering Included Navigation Properties in EF Core: A Comprehensive Guide

Challenge: Filtering a primary query based on a property within a nested navigation property when using Include in Entity Framework Core can be tricky. This guide provides a solution.

Solution: Leveraging Filtered Include

Entity Framework Core 5 introduced Filtered Include, a powerful feature enabling filtering of included navigation properties. Supported operators include Where, OrderBy/OrderByDescending, Skip, and Take.

Implementing Filtered Include:

Let's illustrate with an example:

<code class="language-csharp">var blogs = context.Blogs
    .Include(blog => blog.Posts.Where(post => post.Author == "me"))
    .ThenInclude(post => post.Author)
    .ToList();</code>

This query retrieves blogs and their associated posts, but only includes posts where the author's name is "me". Note the Where clause within the Include method.

Key Considerations:

• Single Filter per Navigation: Only one filter is permitted per navigation property.
• Independent Predicates: Filters within Include are treated as independent predicates.
• Lazy Loading Override: Filtered includes are applied regardless of lazy loading configuration.
• Cumulative Results: Subsequent filtered includes accumulate their results.

Relationship Fixup and Filtered Include:

Be mindful of relationship fixup. It might add extra entries to the navigation property's collection, potentially leading to unexpected results.

Filtered Include vs. Direct Query Filtering:

Filtered Include impacts only the included navigation properties, not the main query. To filter the main query based on a navigation property, use the Where method directly on the DbSet or IQueryable.

Filtered Include and Projections:

Projections generally ignore Include statements, even filtered ones. However, if the Include can be applied to an entity within the projection, it will still be applied.

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