EFCore 初始化配置

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EFCore基础配置与数据迁移cli

EFCore 初始化配置

EFCore官方教程

  1. ef-mvc 教程
  2. ef-mvc 教程 github 源码

基础配置

  1. 引入依赖包

    • MySql.Data.EntityFrameworkCore (官方，很多未完善)
    • Pomelo.EntityFrameworkCore.MySql (Pomelo，官方推荐)

  2. 添加上下文类和实体类

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    > public class SchoolContext : DbContext
    > {
    >     public SchoolContext(DbContextOptions<SchoolContext> options) : base(options)
    >     {
    > 
    >     }
    > 
    >     public DbSet<Course> Courses { get; set; }
    >     public DbSet<Enrollment> Enrollments { get; set; }
    >     public DbSet<Student> Students { get; set; }
    > 
    >     protected override void OnModelCreating(ModelBuilder modelBuilder)
    >     {
    >         modelBuilder.Entity<Course>().ToTable("Course");
    >         modelBuilder.Entity<Enrollment>().ToTable("Enrollment");
    >         modelBuilder.Entity<Student>().ToTable("Student");
    >     }
    > }
    >

  3. 上下文的依赖注入

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    > public void ConfigureServices(IServiceCollection services)
    > {
    >     services.AddDbContext<SchoolContext>(options =>
    >     {
    >         options.UseMySQL(Configuration.GetConnectionString("DefaultConnection"));
    >     });
    >     services.AddMvc();
    > }
    >

  4. 测试数据初始化

    EnsureCreated 这个方法确保数据库被创建

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    public static class DbInitializer
    {
        public static void Initialize(SchoolContext context)
        {
            context.Database.EnsureCreated();

            // Look for any students.
            if (context.Students.Any())
            {
                return;   // DB has been seeded
            }

            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")}
            };
            foreach (Student s in students)
            {
                context.Students.Add(s);
            }
            context.SaveChanges();

            var courses = new Course[]
            {
            new Course{CourseID=1050,Title="Chemistry",Credits=3},
            new Course{CourseID=4022,Title="Microeconomics",Credits=3},
            new Course{CourseID=4041,Title="Macroeconomics",Credits=3},
            new Course{CourseID=1045,Title="Calculus",Credits=4},
            new Course{CourseID=3141,Title="Trigonometry",Credits=4},
            new Course{CourseID=2021,Title="Composition",Credits=3},
            new Course{CourseID=2042,Title="Literature",Credits=4}
            };
            foreach (Course c in courses)
            {
                context.Courses.Add(c);
            }
            context.SaveChanges();

            var enrollments = new Enrollment[]
            {
            new Enrollment{StudentID=1,CourseID=1050,Grade=Grade.A},
            new Enrollment{StudentID=1,CourseID=4022,Grade=Grade.C},
            new Enrollment{StudentID=1,CourseID=4041,Grade=Grade.B},
            new Enrollment{StudentID=2,CourseID=1045,Grade=Grade.B},
            new Enrollment{StudentID=2,CourseID=3141,Grade=Grade.F},
            new Enrollment{StudentID=2,CourseID=2021,Grade=Grade.F},
            new Enrollment{StudentID=3,CourseID=1050},
            new Enrollment{StudentID=4,CourseID=1050},
            new Enrollment{StudentID=4,CourseID=4022,Grade=Grade.F},
            new Enrollment{StudentID=5,CourseID=4041,Grade=Grade.C},
            new Enrollment{StudentID=6,CourseID=1045},
            new Enrollment{StudentID=7,CourseID=3141,Grade=Grade.A},
            };
            foreach (Enrollment e in enrollments)
            {
                context.Enrollments.Add(e);
            }
            context.SaveChanges();
        }
    }

数据迁移

dotnet-ef命令行官方文档（.NET Core CLI）

  1. 添加命令行 Nuget 包

    Microsoft.EntityFrameworkCore.Tools.DotNet 用于 dotnet-ef 命令
    Microsoft.DotNet.Watcher.Tools 这里用于 donet watch run，开发时保存即编译，无需重新run，这里和数据迁移无关

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    <ItemGroup>
      <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="2.0.1"/>
      <DotNetCliToolReference Include="Microsoft.DotNet.Watcher.Tools" Version="2.0.0"/>
    </ItemGroup>

  2. 创建一个数据迁移类

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    dotnet ef migrations add InitialCreate

  3. 应用迁移到数据库

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    dotnet ef database update

  4. XXContextModelSnapshot

    这个类始终与所有迁移同步，如果要撤销迁移，使用 dotnet ef migrations remove 撤销最后一个迁移，而不能删除 <timestamp>_<migrationname>.cs 文件，否则会导致此类 XXContextModelSnapshot 与剩余迁移不同步。