直接从父实体删除实体时，不同的行为

Question

我正在使用EF核心，我想跟踪实体的删除。现在，当当时使用ChangEtracking删除任何实体时，我会记录该实体，也需要记录IT父实体。

在这种情况下，我以简单的例子为例。在这家公司和部门中，有一对一的关系。

using Microsoft.EntityFrameworkCore;

public class SimpleDbContext 
    : DbContext
{
    public DbSet<Company> Companies { get; set; }
    public DbSet<Department> Departments { get; set; }  

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Company>().HasMany(cc => cc.Departments).WithOne(cc => cc.Company);            
        base.OnModelCreating(modelBuilder);
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(@"Data Source=(LocalDb)\MSSQLLocalDB;Initial Catalog=sampletracking;Integrated Security=SSPI");
        base.OnConfiguring(optionsBuilder);
    }

    public override Task<int> SaveChangesAsync(bool acceptAllChangesOnSuccess, CancellationToken cancellationToken = default)
    {
        foreach(var item in this.ChangeTracker.Entries())
        {
            if(item.State == EntityState.Deleted)
            {
                foreach(var itemRef in item.References)
                {
                    if (!itemRef.IsLoaded)
                        itemRef.Load();
                }
            }
        }

        return base.SaveChangesAsync(acceptAllChangesOnSuccess, cancellationToken);
    }
}

恩典

public class Company
{
    public int Id { get; set; }
    public string CompanyName { get; set; }
    public List<Department> Departments { get; set; }
}

public class Department
{
    public int Id { get; set; }
    public string DepartmentName { get; set; }
    public Company Company { get; set; }
}

准备记录。

using (SimpleDbContext simpleDbContext = new SimpleDbContext())
{
    Company company = new Company();
    company.CompanyName = "Company-1";
    company.Departments = new List<Department>();
    company.Departments.Add(new Department() { DepartmentName = "Department-1" });
    company.Departments.Add(new Department() { DepartmentName = "Department-2" });
    simpleDbContext.Add(company);
    await simpleDbContext.SaveChangesAsync();
}

方案1：删除儿童实体直接。

using (SimpleDbContext simpleDbContext = new SimpleDbContext())
{
    var department = simpleDbContext.Departments.Where(cc => cc.Id == 1).FirstOrDefault();
    simpleDbContext.Remove(department);
    await simpleDbContext.SaveChangesAsync();
}

在这种情况下，当SaveChange调用时，更改跟踪器检测删除及其加载引用（SO parent实体）时，然后成功加载。

方案2：

using (SimpleDbContext simpleDbContext = new SimpleDbContext())
{
    var company = simpleDbContext.Companies
        .Include(cc => cc.Departments)
        .Where(cc => cc.Id == 1).FirstOrDefault();

    company.Departments.RemoveAll(cc => cc.Id == 2);
    
    await simpleDbContext.SaveChangesAsync();
}

正在检测到此方案实体删除中删除的情况下，但是当它尝试加载参考时，它始终是null。

为什么如果相同的实体从同一集合中删除它的行为不同？