Entity Framework Core树状结构增删改查

谁践踏了优雅 2021-07-26 16:50 311阅读 0赞

首先创建一个.net core控制台程序，添加实体类

## 实体类:Employee ##

using System.Collections.Generic;
    using System.ComponentModel.DataAnnotations.Schema;
    
    namespace TreeEntityDemo
    {
        /// <summary>
        /// 员工实体
        /// </summary>
        public class Employee
        {
            public int Id { get; set; }
            public string Name { get; set; }
    
            [ForeignKey(nameof(ManagerId))]
            public int? ManagerId { get; set; }
            public virtual Employee Manager { get; set; }
            public virtual ICollection<Employee> Employees { get; set; }
        }
    }

## 定义DbContext ##

using Microsoft.EntityFrameworkCore;
    using Microsoft.Extensions.Configuration;
    using System.IO;
    
    namespace TreeEntityDemo
    {
        public class AppDbContext:DbContext
        {
            public AppDbContext()
            {
    
            }
            public AppDbContext(DbContextOptions<AppDbContext> options):base(options)
            {
    
            }
            public DbSet<Employee> Employees { get; set; }
    
            protected override void OnModelCreating(ModelBuilder modelBuilder)
            {
                modelBuilder.Entity<Employee>()
                    .HasMany(x => x.Employees)
                    .WithOne(x => x.Manager)
                    .HasForeignKey(x => x.ManagerId)
                    .OnDelete(DeleteBehavior.ClientSetNull);
            }
    
            protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            {
                var builder = new ConfigurationBuilder()
                    .SetBasePath(Directory.GetCurrentDirectory())
                    .AddJsonFile("appsettings.json");
                var config = builder.Build();
                optionsBuilder.UseSqlServer(config.GetConnectionString("TreeDemoDb"));
    
            }
        }
    }

## 配置数据库链接:appsettings.json ##

{ 
      "ConnectionStrings": { 
        "TreeDemoDb": "Server=(localdb)\\MSSQLLocalDB;Database=TreeDemoDb;Trusted_Connection=True;MultipleActiveResultSets=true"
      }
    }

## 添加数据库迁移 Add-Migration ##

add-migration InitialCreate

## 在Program.cs中测试 ##

using Microsoft.EntityFrameworkCore;
    using System;
    using System.Linq;
    
    namespace TreeEntityDemo
    {
       class Program
       {
           static void Main(string[] args)
           {
               using (var context = new AppDbContext())
               {
                   context.Database.EnsureCreated();
                   if (!context.Employees.Any())
                   {
                       context.Employees.AddRange(
                           new Employee()
                           {
                               Name = "Manager1"
                           },
                           new Employee()
                           {
                               Name = "Employee1"
                           },
                           new Employee()
                           {
                               Name = "Employee2"
                           },
                           new Employee()
                           {
                               Name = "Employee3"
                           }
                       );
                   }
                   context.SaveChanges();
               }
               //GetParent();
               SetParent();
               GetChildren();
               Console.WriteLine("Done!");
           }
          
           public static void Find()
           {
               using (var context = new AppDbContext())
               {
                   var employees = context.Employees.FirstOrDefault(t => t.Name == "Employee1");
                   Console.WriteLine(employees.Name);
                   Console.WriteLine(employees.Manager.Name);
               }
           }
    
           /// <summary>
           /// 删除所有
           /// </summary>
           static void RemoveAll()
           {
               using (var context = new AppDbContext())
               {
                   var employees = context.Employees
                       .Where(t => !string.IsNullOrEmpty(t.Name));
                   context.RemoveRange(employees);
                   context.SaveChanges();
               }
           }
    
           /// <summary>
           /// 获取父类
           /// </summary>
           static void SetParent()
           {
               using (var context = new AppDbContext())
               {
                   var employee1 = context.Employees.FirstOrDefault(t => t.Name == "Employee1");
                   var employee2 = context.Employees.FirstOrDefault(t => t.Name == "Employee2");
                   var employee3 = context.Employees.FirstOrDefault(t => t.Name == "Employee3");
                   var manager1 = context.Employees.FirstOrDefault(t => t.Name == "Manager1");
                   employee1.Manager = manager1;
                   employee2.Manager = manager1;
                   employee3.Manager = manager1;
                   context.Update(employee1);
                   context.Update(employee2);
                   context.Update(employee3);
                   context.SaveChanges();
               }
           }
    
           /// <summary>
           /// 获取子类
           /// </summary>
           static void GetParent()
           {
               using (var context = new AppDbContext())
               {
                   var employee1 = context.Employees.Include(t=>t.Manager).FirstOrDefault(t => t.Name == "Employee1");
                   if (employee1.Manager==null)
                   {
                       Console.WriteLine("null");
                   }
                   else
                   {
                       Console.WriteLine(employee1.Manager.Name);
                   }
               }
           }
    
           static void GetChildren()
           {
               using (var context = new AppDbContext())
               {
                   var manager1 = context.Employees.FirstOrDefault(t => t.Name == "Manager1");
                   var children = context.Employees.Where(t => t.ManagerId == manager1.Id);
                   if (children!=null && children.Count()>0)
                   {
                       foreach (var item in children)
                       {
                           Console.WriteLine(item.Name);
                       }
                   }
                   
               }
           }
    
           static void DeleteParent()
           {
               using (var context = new AppDbContext())
               {
                   var manager1 = context.Employees.FirstOrDefault(t => t.Name == "Manager1");
    
                   context.Employees.Remove(manager1);
                   context.SaveChanges();
               }
           }
    
       }
    }