初识EFCore

谁践踏了优雅 2024-03-30 14:12 101阅读 0赞

## 一、开发环境的配置 ##

### 1、新建一个控制台项目，在其中创建一个book实体类 ###

using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    
    namespace EFCoreTest1
    {
        public class Book
        {
            public long Id { get; set; } //主键
    
            public string Title { get; set; }//标题
            
            public DateTime PubTime { get; set; }//发布日期
            public double Price { get; set; }//单价
    
            public string AuthorName { get; set; }//作者名字
        }
    }

### 2、在新建的项目中安装**NutGet**包**Microsoft.EntityFrameworkCore.SqlServer** ###

![e4a15c131c789d4a54aaeb215854b2d6.png][]

1.  、安装命令

Install-Package Microsoft.EntityFrameworkCore.SqlServer

![e552d1ac32787e5f14998c096af46804.png][]

### 3、创建实现了IEntityTypeConfiguration接口的实体类的配置类BookEntityConfig ###

*  **这个实体类的作用就是配置实体类和对应表的关系**

using Microsoft.EntityFrameworkCore.Metadata.Builders;
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    
    namespace EFCoreTest1
    {
        class BookConfig : IEntityTypeConfiguration<Book>
        {
            public void Configure(EntityTypeBuilder<Book> builder)
            {
                //
                builder.ToTable("T_Books");
                builder.Property(b => b.Title).HasMaxLength(50).IsRequired();
                builder.Property(b => b.AuthorName).HasMaxLength(50).IsRequired();
            }
        }
    }

只设置了一个表名T\_Books

*  约定大于配置：

可以不用对实体类做任何的配置，它会按照约定的规则把数据库建好

这里其实可以不用建这个类

### 4、创建一个继承自DbContext类的MyDbContext类 ###

using Microsoft.EntityFrameworkCore;
    using Microsoft.Extensions.Logging;
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    
    namespace EFCoreTest1
    {
        class MyDbContext:DbContext
        {
            //private static ILoggerFactory loggerFactory = LoggerFactory.Create(b=>b.AddConsole());
            public DbSet<Book> Books { get; set; }
            public DbSet<Person> Persons { get; set; }
    
            public DbSet<Dog> Dogs { get; set; }
    
            protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            {
                base.OnConfiguring(optionsBuilder);
                optionsBuilder.UseSqlServer("Server=.;Database=demo1;Trusted_Connection=True;MultipleActiveResultSets=true;Encrypt=True;TrustServerCertificate=True;");
    
                //optionsBuilder.UseLoggerFactory(loggerFactory);
                /*optionsBuilder.LogTo(msg =>
                {
                    if (!msg.Contains("CommandExecuting")) return;
                    Console.WriteLine(msg);
                });*/
            }
    
            protected override void OnModelCreating(ModelBuilder modelBuilder)
            {
                base.OnModelCreating(modelBuilder);
                //从当前程序集中加载所有的IEntityTypeConfiguration
                modelBuilder.ApplyConfigurationsFromAssembly(this.GetType().Assembly);
            }
        }
    }

*  OnConfiguring方法用于对程序要连接的数据库进行配置：

指定连接字符串以及连接那个数据库

optionsBuilder.UseSqlServer("Server=.;Database=demo1;Trusted_Connection=True;MultipleActiveResultSets=true;Encrypt=True;TrustServerCertificate=True;");

*  OnModelCreating方法:配置类所在的程序集

modelBuilder.ApplyConfigurationsFromAssembly(this.GetType().Assembly);

### 5、生成数据库 ###

*  通过NuGet为项目安装Microsoft.EnityFrameworkCore.Tools包，这是为了使用EF Core生成数据库工具

Install-Package Microsoft.EnityFrameworkCore.Tools

*  然后在执行**Add-Migration**命令会自动在项目的Migrations文件夹中生成C\#代码

![d2ad155151ee48abb0864f1f9bf221df.png][]

*  最后执行**Update-database**命令那些在Migrations 文件夹中用来创建数据库表的代码才会被应用到数据库中

![aa77a719fd103f81bb5019f319fd0470.png][]

结果最后是这样的

![2396e2ce1c83291e35718eb02a3ed64e.png][]

## 二、增删改查操作 ##

1.  插入数据

在program中操作

using Microsoft.EntityFrameworkCore;
    using System.Linq;
    namespace EFCoreTest1
    {
        internal class Program
        {
            static async Task Main(string[] args)
            {
                //创建逻辑上的数据库
                using (MyDbContext myDbContext = new MyDbContext())
                {
                   Dog d = new Dog();
                   d.Name = "Trump";
                   myDbContext.Dogs.Add(d);
                    //相当于update-Datebase 异步保存
                    await myDbContext.SaveChangesAsync();                                   
                }
            }
        }
    }

数据库结果

![21817b7ee620a6f9678604fd7a0ad283.png][]

在插入一部分数据，为查看数据做铺垫

Book b1 = new Book
                    {
                        AuthorName = "杨中科",
                        Title = "零基础学C语音",
                        Price = 59.8,
                        PubTime = new DateTime(2019, 3, 1)
                    };
                    Book b2 = new Book
                    {
                        AuthorName = "Robert Sedgewick",
                        Title = "算法（第四版）",
                        Price = 99,
                        PubTime = new DateTime(2012, 10, 1)
                    };
                    Book b3 = new Book
                    {
                        AuthorName = "吴军",
                        Title = "数学之美",
                        Price = 69,
                        PubTime = new DateTime(2020, 5, 1)
                    };
                    Book b4 = new Book
                    {
                        AuthorName = "杨中科",
                        Title = "程序员的SQL金典",
                        Price = 52,
                        PubTime = new DateTime(2008, 9, 1)
                    };
                    Book b5 = new Book
                    {
                        AuthorName = "吴军",
                        Title = "文明之光",
                        Price = 246,
                        PubTime = new DateTime(2017, 3, 1)
                    };
                    //把对象加入逻辑上的表上面
                    myDbContext.Books.Add(b1);
                    myDbContext.Books.Add(b2);
                    myDbContext.Books.Add(b3);
                    myDbContext.Books.Add(b4);
                    myDbContext.Books.Add(b5);
                    //相当于update-Datebase 异步保存
                    await myDbContext.SaveChangesAsync();

数据库结果

![00588d856ca27b935ee738652f263f6c.png][]

### 2、查询数据 ###

1、DbSet实现了IEnumerable<T>接口，因此可以对DbSet实施Linq操作来进行数据查询。EF Core会把Linq操作转换为SQL语句。面向对象，而不是面向数据库(SQL)。

2、ctx.Books.Wkere(b => b.Price > 80)

Book b1 = ctx.Books.Single(b => b.Title== "零基础趣学C语言");

Book b2 = ctx.Books.FirstOrDefault(b=>b.Id==9);

3、可以使用OrderBy操作进行数据的排序

IEnumerable <Book> books =ctx. Books. OrderByDescending(b => b.Price);

*  查询语句

IQueryable<Book> books = myDbContext.Books.Where(b => b.Price > 80);
                    foreach(var book in books)
                    {
                        Console.WriteLine(book.Title);
                    }

也可以写成

var books = myDbContext.Books.Where(b => b.Price > 80);
                    foreach(var book in books)
                    {
                        Console.WriteLine(book.Title);
                    }

查询结果为

![0a82b85d06c0764df02c8e92cd49eabc.png][]

**查询就不需要** **await myDbContext.SaveChangesAsync();****了**

*  查询单个

var Book = myDbContext.Books.Single(b => b.Title == "零基础学C语言");
                    Console.WriteLine(Book.AuthorName);

*  按照价格排序

var books = myDbContext.Books.OrderBy(b => b.Price).Where(b=>b.Price>60);
                    foreach(var book in books)
                    {
                        Console.WriteLine(book.Title+","+book.Price);
                    }

*  结果

![717b90fcdcfbcf19a0786beaa658c8c1.png][]

**这里有重复的是因为我添加数据添加了两次导致的**

### 三、修改、删除 ###

**要对数据进行修改，首先需要把要修改的数据查询出来，然后再对查询出来的对象进行操作，然后再执行SaveChangesAsync()**

var b = myDbContext.Books.Single(b => b.Title == "数学之美");
                    b.AuthorName = "junwu";
    
                    Dog dog = myDbContext.Dogs.Single(b => b.Id == 2);
    
                    myDbContext.Dogs.Remove(dog);
                    await myDbContext.SaveChangesAsync();

[e4a15c131c789d4a54aaeb215854b2d6.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/354344684fa3415e8525318c690f43dc.png
[e552d1ac32787e5f14998c096af46804.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/d1fbee320d654f1c9b57cd47fcd8513b.png
[d2ad155151ee48abb0864f1f9bf221df.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/89b73db7e409496981273c73092552d4.png
[aa77a719fd103f81bb5019f319fd0470.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/46204038f32345fabfadd9947f732d0d.png
[2396e2ce1c83291e35718eb02a3ed64e.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/614e974946b64e31b35b2c41d714094d.png
[21817b7ee620a6f9678604fd7a0ad283.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/74bb0f5e10f24a9b84d178005dbddf38.png
[00588d856ca27b935ee738652f263f6c.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/4732f72bd85a457fa128c2b24ac80e98.png
[0a82b85d06c0764df02c8e92cd49eabc.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/fc03186414a2467e8f659b0a3b7f09b4.png
[717b90fcdcfbcf19a0786beaa658c8c1.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/d6eec05f2cfa40b1b6b93e667fb56b00.png