EFCore 急切加载问题

Question

I'm a little bit stumped as to why this is not working in EF Core 3.1.8 and SQLite. I have a compound foreign key relationship between two entities with an int and Guid. When I try to eager load all stores with store sections, the StoreSection navigation property is not returning any results.

I've checked the created tables and the data is saving as expected. I've checked the optimized sql generated and when I run it directly, the results return what I expect. Below is a console application demonstrating the problem.

using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;

namespace TestEfcore
{
    class Program
    {
        static void Main()
        {
            Guid userId = Guid.NewGuid();

            using (var context = new GroceryManagerContext())
            {
                var newStore = new Store
                {
                    Name = "Grocery World",
                    GroceryManagerUserId = userId
                };

                newStore.StoreSections.Add(new StoreSection() { Name = "Deli", GroceryManagerUserId = userId });

                newStore.StoreSections.Add(new StoreSection() { Name = "Produce", GroceryManagerUserId = userId });

                context.Add(newStore);
                context.SaveChanges();
            }
            
            using (var context = new GroceryManagerContext())
            {
                // Attempting to eager load store sections.
                var stores = context.Stores
                   .Include(s => s.StoreSections)
                   .Where(s => s.GroceryManagerUserId == userId)
                   .ToList();

                Console.WriteLine($"The user guid is {userId}.");

                foreach (var store in stores)
                {
                    Console.WriteLine($"There are {store.StoreSections.Count} store sections in {store.Name}.");
                }
            }
        }

        public class Store
        {
            public int StoreId { get; set; }

            public string Name { get; set; } = string.Empty;

            public Guid GroceryManagerUserId { get; set; }

            public List<StoreSection> StoreSections { get; } = new List<StoreSection>();
        }

        public class StoreSection
        {
            public int StoreSectionId { get; set; }

            public string Name { get; set; } = string.Empty;

            public Guid GroceryManagerUserId { get; set; }

            public int StoreId { get; set; }
            public Store Store { get; set; } = new Store();
        }

        public class GroceryManagerContext : DbContext
        {
            public DbSet<Store>? Stores { get; set; }

            public DbSet<StoreSection>? StoreSections { get; set; }

            protected override void OnModelCreating(ModelBuilder builder)
            {
                if (builder == null)
                    throw new ArgumentNullException(nameof(builder));

                base.OnModelCreating(builder);

                builder.Entity<Store>()
                    .HasIndex(s => new { s.Name, s.GroceryManagerUserId })
                    .IsUnique();

                builder.Entity<StoreSection>()
                    .HasIndex(ss => new { ss.Name, ss.GroceryManagerUserId })
                    .IsUnique();

                builder.Entity<StoreSection>()
                    .HasOne(ss => ss.Store)
                    .WithMany(s => s.StoreSections)
                    .HasForeignKey(ss => new { ss.StoreId, ss.GroceryManagerUserId })
                    .HasPrincipalKey(s => new { s.StoreId, s.GroceryManagerUserId })
                    .IsRequired();
            }

            protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            {
                optionsBuilder.UseSqlite(@"Data Source=D:\src\TestEfcore\TestEfcore\GroceryManager.db");
            }
        }
    }
}

Answer 1

The StoreSections navigation property is not eager loading because you are initializing the Store property on StoreSection entity with the new operator.

This is causing the StoreSection.StoreId property to be saved with a 0 which prevents the association from being created

You'll want to change the StoreSection entity to remove the initialization to resolve the problem:

public class StoreSection
{
    public int StoreSectionId { get; set; }

    public string Name { get; set; } = string.Empty;

    public Guid GroceryManagerUserId { get; set; }

    public int StoreId { get; set; }
    public Store Store { get; set; } // initialization has been removed here
}