Efcore tuning

Initialization data ：

using Microsoft.Extensions.Configuration;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFCoreDemon1
{
    
    internal class MyDbContext:DbContext
    {
    
        public DbSet<Article> Articles {
     get; set; } //API The name of 
        public DbSet<Comment> Comments {
     get; set; }
        public DbSet<Comment2> Comment2s {
     get; set; }
        public DbSet<Customers> Customers {
     get; set; } //API The name of 
        public DbSet<Orders> Orders {
     get; set; }

        private ConfigurationBuilder cfgBuilder = new ConfigurationBuilder();


        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
    
            base.OnConfiguring(optionsBuilder);
            //Microsoft.Extensions.Configuration.JsonConfigurationExtensions
            cfgBuilder.AddJsonFile("DbCfg.json", optional: true, reloadOnChange: true);
            IConfigurationRoot configRoot = cfgBuilder.Build();
            string connString = configRoot.GetSection("ConnectionStrings:SqliteConnectionString").Value;
            optionsBuilder.UseSqlite(connString);
        }
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
    
            base.OnModelCreating(modelBuilder);
            modelBuilder.Entity<Customers>()
                .HasData
                (
                new Customers {
     Id = 1, Name = "Joe" },
                new Customers {
     Id = 2, Name = "Henry" },
                new Customers {
     Id = 3, Name = "Sam" },
                new Customers {
     Id = 4, Name = "Max" }
                );
            modelBuilder.Entity<Orders>()
                .HasData
                (
                new Orders {
     Id = 1, Name = "DDD", CustomerId = 3, CustomerId2 = 3 },
                new Orders {
     Id = 2, Name = "EEE", CustomerId = 1, CustomerId2 = 1 },
                new Orders {
     Id = 3, Name = "FFF", CustomerId = 2 },
                new Orders {
     Id = 4, Name = "GGG", CustomerId = 4 }
                );
            modelBuilder.Entity<Comment2>()
                .HasData
                (
                new Comment2 {
     Id = 1, Message = "Orders1 The comments ", OrdersId = 1 },
                new Comment2 {
     Id = 2, Message = "Orders1 The comments ", OrdersId = 1 },
                new Comment2 {
     Id = 3, Message = "Orders2 The comments ", OrdersId = 2 },
                new Comment2 {
     Id = 4, Message = "Orders2 The comments ", OrdersId = 2 },
                new Comment2 {
     Id = 5, Message = "Orders3 The comments ", OrdersId = 3 },
                new Comment2 {
     Id = 6, Message = "Orders3 The comments ", OrdersId = 3 },
                new Comment2 {
     Id = 7, Message = "Orders3 The comments ", OrdersId = 3 },
                new Comment2 {
     Id = 8, Message = "Orders4 The comments ", OrdersId = 4 }
                );
            modelBuilder.ApplyConfigurationsFromAssembly(this.GetType().Assembly);
        }
    }
}

json To configure

{
    
  "ConnectionStrings": {
    
    "SqliteConnectionString": "Data Source=D:\\Db\\DbSqlite.db",
    "MySQLConnectionString": "server=127.0.0.1; database=OneToMany; uid=root; pwd=123456;"
  }
}

result ：

// See https://aka.ms/new-console-template for more information
global using EFCoreDemon1;
global using EFCoreDemon1.Entities;
global using Microsoft.EntityFrameworkCore;
global using Microsoft.EntityFrameworkCore.Metadata.Builders;
using System.Data.Common;


// A website contains two tables ,Customers  Table and  Orders  surface . Write a  SQL  Inquire about , Find all customers who never order anything .

using MyDbContext myDb = new MyDbContext();

var customers = myDb.Orders.Where(o=>o.CustomerId2 == null).Select(o=>o.Customers);

// for the first time Select  Point to a collection through a foreign key , From entering Orders The other table Customers, the second select  Use select Select the specified field 
var name = myDb.Orders.Where(o => o.CustomerId2 == null).Select(o => o.Customers).Select(c => c.Name);

// for the first time Select  Point to a collection through a foreign key , from Customers Enter another table Orders, the second select, from Orders Enter table Comment2
var test = myDb.Customers.Where(c => c.Id > 1).Select(c => c.Orders).Where(o => o.Name == "DDD").Select(o => o.Comment2s);
//var a = myDb.Customers.FromSqlInterpolated($"Select * from Orders").ToList();
//myDb.Orders.FromSqlInterpolated($"Select Name From Customers where Customers.Id not in ()")

foreach (var item in customers)
{
    
    Console.WriteLine(item.Name);
}
Console.WriteLine("=======================");
foreach (var item in name)
{
    
    Console.WriteLine(item);
}
Console.WriteLine("=======================");

// The relationship between the last two tables is one to many , Must be cycled twice 
foreach (var item in test)
{
    
    foreach (var i in item)
    {
    
        Console.WriteLine(i.Message);
    }
}

/*  result  Henry Max ======================= Henry Max ======================= Orders1 The comments  Orders1 The comments  */


// Write primitive  AdoNetCore
Console.WriteLine("=======================");
DbConnection conn = myDb.Database.GetDbConnection();

if (conn.State != System.Data.ConnectionState.Open)
{
    
    await conn.OpenAsync();
}

using (var cmd = conn.CreateCommand())
{
    
    cmd.CommandText = "select Customers.name from Customers where Customers.Id in (select CustomerId2 from Orders)";
    using(var reader = await cmd.ExecuteReaderAsync())
    {
    
        while (await reader.ReadAsync())
        {
    
            var test1 = reader.GetValue(0);
            Console.WriteLine(test1);
        }
    }
}

/*  result ： Joe Sam */

Entity class and configuration ：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFCoreDemon1.Entities
{
    
    public class Customers
    {
    
        public int Id {
     get; set; }
        public string Name {
     get; set; }
        public Orders Orders {
     get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFCoreDemon1.Entities
{
    
    public class Orders
    {
    
        public int Id {
     get; set; }
        public string Name {
     get; set; }
        public Customers Customers {
     get; set; }
        public int CustomerId {
     get; set; }
        public int? CustomerId2 {
     get; set; }
        public List<Comment2> Comment2s {
     get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFCoreDemon1.Entities
{
    
    public class Comment2
    {
    
        public int Id {
     get; set; }
        public Orders Orders {
     get; set; }
        public int OrdersId {
     get; set; } // Foreign keys 
        public string Message {
     get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFCoreDemon1.Db
{
    
    public class CustomersConfig : IEntityTypeConfiguration<Customers>
    {
    
        public void Configure(EntityTypeBuilder<Customers> builder)
        {
    
            builder.ToTable("Customers");
            builder.HasKey(c => c.Id); // Set primary key 
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFCoreDemon1.Db
{
    
    public class OrdersConfig : IEntityTypeConfiguration<Orders>
    {
    
        public void Configure(EntityTypeBuilder<Orders> builder)
        {
    
            builder.ToTable("Orders");
            builder.HasKey(a => a.Id); // Set primary key 
            builder.HasOne<Customers>(o => o.Customers)
                .WithOne(c => c.Orders).HasForeignKey<Orders>(o => o.CustomerId);
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFCoreDemon1.Db
{
    
    public class Comment2Config : IEntityTypeConfiguration<Comment2>
    {
    
        public void Configure(EntityTypeBuilder<Comment2> builder)
        {
    
            builder.ToTable("Comment2");
            builder.HasKey(a => a.Id); // Set primary key 
            builder.HasOne<Orders>(c => c.Orders)
                .WithMany(o => o.Comment2s)
                .HasForeignKey(o => o.OrdersId);
        }
    }
}