.net core EF codefirst

前言

操作方法与Framework类似，使用前先下载EF依赖包

Install-Package Microsoft.EntityFrameworkCore.SqlServer -version 3.1.1

先定义数据表的类

   //例如有一张学生表
   public class Student
    {
        public int ID { get; set; }
        public string LastName { get; set; }
        public string FirstMidName { get; set; }
        public DateTime EnrollmentDate { get; set; }

        public ICollection<Enrollment> Enrollments { get; set; }
    }

在创建上下文对象的类

此类需要继承 Microsoft.EntityFrameworkCore.DbContext 类

 public class SchoolContext : DbContext
    {
        public SchoolContext(DbContextOptions<SchoolContext> options) : base(options)
        {
        }
        //上下文对象的类名就是数据库的名称
        //添加数据表Students为创建的表名
        public DbSet<Student> Students { get; set; }
    }

提供创建数据库的类

   public static class DbInitializer
    {
        public static void Initialize(SchoolContext context)
        {
        //创建数据库，返回布尔值
          var isscuess = context.Database.EnsureCreated();
                }
        }

启动文件中调用创建数据库的方法

//main函数中调用创建数据库
 public static void Main(string[] args)
        {
            //CreateHostBuilder(args).Build().Run();

            var host = CreateHostBuilder(args).Build();
            CreateDbIfNotExists(host);
            host.Run();

        }

 //如果数据库不存在就创建的方法
 private static void CreateDbIfNotExists(IHost host)
        {
            using (var scope = host.Services.CreateScope())
            {
                var services = scope.ServiceProvider;
                var context = services.GetRequiredService<SchoolContext>();
                DbInitializer.Initialize(context);
            }
        }

配置文件appsettings.json中配置连接数据库的字符串

"ConnectionStrings": {
    "SchoolContext": "Server=.;Database=SchoolContext;uid=sa;password=123456"
  },

首先添加上下文的依赖,GetConectionString中的参数是配置文件中的参数

services.AddDbContext<SchoolContext>(options => options.UseSqlServer(Configuration.GetConnectionString("SchoolContext")));

在控制器中添加依赖注入，构造函数添加

//定义一个私有只读的实例
 private readonly SchoolContext schoolContext;
 
 //构造函数注入
  public HomeController(SchoolContext _schoolContext)
        {
            schoolContext = _schoolContext;
        }

注入完成过后，往数据库添加数据

//定义一个数组
  var students = new Student[]
            {
                new Student{FirstMidName="Carson",LastName="Alexander",EnrollmentDate=DateTime.Parse("2005-09-01")},
                new Student{FirstMidName="Meredith",LastName="Alonso",EnrollmentDate=DateTime.Parse("2002-09-01")},
                new Student{FirstMidName="Arturo",LastName="Anand",EnrollmentDate=DateTime.Parse("2003-09-01")},
                new Student{FirstMidName="Gytis",LastName="Barzdukas",EnrollmentDate=DateTime.Parse("2002-09-01")},
                new Student{FirstMidName="Yan",LastName="Li",EnrollmentDate=DateTime.Parse("2002-09-01")},
                new Student{FirstMidName="Peggy",LastName="Justice",EnrollmentDate=DateTime.Parse("2001-09-01")},
                new Student{FirstMidName="Laura",LastName="Norman",EnrollmentDate=DateTime.Parse("2003-09-01")},
                new Student{FirstMidName="Nino",LastName="Olivetto",EnrollmentDate=DateTime.Parse("2005-09-01")}
            };
            //写入数据缓冲区
            foreach (Student s in students)
            {
                schoolContext .Students.Add(s);
            }
            //真正的写入数据库
            schoolContext .SaveChanges();

数据库显示

 var name = schoolContext.Students.Where(a => a.ID == 5).Select(a => a.FirstMidName).FirstOrDefault();