Question

我使用Entity Framework Core 2.2和代码优先方法。在数据库中有一个表，我们将其简化为Department。

public class Department
{
    public int Id { get; set; }
    public int ? ParentId { get; set; }
    public string DepartmentName { get; set; }
    public ICollection<Department> InnerDepartments { get; set; }
}

我使用Fluent API定义了配置，并生成了我想要的结构。

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
        modelBuilder.Entity<Department>().HasKey(p => p.Id);
        modelBuilder.Entity<Department>().HasMany(p => p.InnerDepartments)
            .WithOne(p => p.TopDepartment)
            .HasForeignKey(p => p.TopDepartmentId);

        base.OnModelCreating(modelBuilder);
}

例如，我可能有以下数据。

Id  TopDepartmentId  DepartmentName
-----------------------------------------
1      NULL          Software Development
2       1            Mobile Development
3       1            Web Development
4       2            IOS Development
5       2            Android Development
6       4            Swift Development
7       4            Objective-C Development

我想将此表中的数据排列为以下结构：

public class DepartmentShortInfoModel
{
    public int DepartmentId { get; set; }
    public string DepartmentName { get; set; }
    public int DirectInnerDepartmentsCount { get; set; }
    public int IndirectInnerDepartmentsCount { get; set; }
}

这意味着对于每个部门客户来说，要获取直接内部部门的数量-（第一级深度子代数），例如，移动部门有2个直接子部门-IOS和Android部门。同时，客户想知道间接内部部门的数量，移动部门有4个间接子级-IOS，Android，Swift，Objective-C，因为Swift和Objective-C是移动部门子级的子级。

我尝试通过递归树遍历算法实现此功能。

private int GetChildrenDepartmentCount(
        Department department, 
        bool useRecursionForTraversal = false)
    {
        int numberOfChildrenInCurrentLevel = department.InnerDepartments?.Count() ?? 0;

        if (useRecursionForTraversal == false)
            return numberOfChildrenInCurrentLevel;

        if (folder.Children != null)
            return numberOfChildrenInCurrentLevel +
                folder.Children.Select(p => GetChildrenDepartmentCount(p, useRecursionForTraversal)).Sum();
        else return numberOfChildrenInCurrentLevel ;
    }

我通过热切的加载方式从DbContext加载数据。

using(var context = new DepartmentContext(options))
{
            var department = context.Departments.Include(p => p.InnerDepartments)
                                                .First(p => p.Id == 1);
}

但是，问题是EF仅加载1级子级（移动和Web），而对于以下级别，EF在InnerDepartments属性中返回NULL。

如何请求EF也加载内部级别？我在社区建议使用SelectMany的地方读过类似的问题，但是这里的问题出在InnerDepartments属性的NULL中，而不是在LINQ查询中获取内部值。

Answer 1

尝试以下操作：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;

namespace ConsoleApplication116
{
    class Program
    {
        static DataTable dt;
        static void Main(string[] args)
        {
            dt = new DataTable();
            dt.Columns.Add("Id", typeof(int));
            dt.Columns.Add("TopDepartmentId", typeof(int));
            dt.Columns.Add("DepartmentName", typeof(string));

            dt.Rows.Add(new object[] { 1, null, "Software Development" });
            dt.Rows.Add(new object[] { 2, 1, "Mobile Development" });
            dt.Rows.Add(new object[] { 3, 1, "Web Development" });
            dt.Rows.Add(new object[] { 4, 2, "IOS Development" });
            dt.Rows.Add(new object[] { 5, 2, "Android Development" });
            dt.Rows.Add(new object[] { 6, 4, "Swift Development" });
            dt.Rows.Add(new object[] { 7, 4, "Objective-C Development" });

            GetTree(null, 0);
            Console.ReadLine();
        }
        static void GetTree(int? parent, int level)
        {
            DataRow[] children = dt.AsEnumerable().Where(x => x.Field<int?>("TopDepartmentId") == parent).ToArray();
            foreach (DataRow child in children)
            {
                int childId = child.Field<int>("Id");
                Console.WriteLine("{0}ID : '{1}', TopDepartmentId : '{2}', DepartmentName : '{3}'", 
                    new string(' ', 5 * level), //ident each level
                    childId.ToString(), 
                    (child.Field<object>("TopDepartmentId") == null) ? "BOSS" : child.Field<int?>("TopDepartmentId").ToString(),
                    child.Field<string>("DepartmentName"));

                GetTree(childId, level + 1);
            }
        }

    }

}

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1 个答案: