How Can EF Core Efficiently Map a Self-Referencing Category Table for Hierarchical Data Retrieval?

Mapping Self-Referencing Category Table Structure to EF Core

The problem arises from the complexity of retrieving a hierarchical structure, such as the category table with its ParentId column, within the limitations of EF Core and LINQ. To address this, a recursive function was employed to manually traverse the categories and populate the ChildCategories property.

However, a more efficient solution leveraging EF Core's full capabilities has emerged:

Using a Single Include

Unlike previous attempts to load a portion of the tree with Include(), this approach involves a single Include() on the ChildCategories property. This, combined with the materialization of the query into a LINQ to Objects context, allows EF Core's navigation property fixup to handle the mapping.

Optimized Retrieval with Filtering

To retrieve only the root nodes of the category tree, as required by the repository's GetAll() method, a filter is applied after the query has been materialized:

return Table
       .AsEnumerable()
       .Where(x => x.ParentId == null)
       .ToList();

By materializing the query into a LINQ to Objects context using AsEnumerable(), the navigation properties are fixed before filtering is applied. This results in a single SQL query that effectively retrieves the desired hierarchical structure without the need for recursive functions.

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