8.Entity Framework Core数据库种子

在 Program.cs 中添加种子初始值设定项代码。

using ContosoUniversity.Models;

var app = builder.Build();

using (var scope = app.Services.CreateScope())
{
    var services = scope.ServiceProvider;

    SeedData.Initialize(services);
}

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

右键单击Data文件夹或Models文件夹-添加–类-名称SeedData.cs。SeedData静态类名和Initialize静态方法名可以是任意的名称。

如果数据库中有任何学生，则不会添加任何学生并返回到种子初始值设定项继续往下执行。

using ContosoUniversity.Data;
using Microsoft.EntityFrameworkCore;

namespace ContosoUniversity.Models
{
    public static class SeedData
    {
        public static void Initialize(IServiceProvider serviceProvider)
        {
            using (var context = new SchoolContext(
                serviceProvider.GetRequiredService<
                    DbContextOptions<SchoolContext>>()))
            {
                // 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();
            }
        }
    }
}