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Core EF Code First-黑色主题效果
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2020/12/18 16:27
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[TOC] <br/> ####创建好实体 Student类: ```c# 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; } } ``` Course类: ```c public class Course { [DatabaseGenerated(DatabaseGeneratedOption.None)] public int CourseID { get; set; } public string Title { get; set; } public int Credits { get; set; } public ICollection<Enrollment> Enrollments { get; set; } } ``` Enrollment类: ``` public enum Grade { A, B, C, D, F } public class Enrollment { public int EnrollmentID { get; set; } public int CourseID { get; set; } public int StudentID { get; set; } public Grade? Grade { get; set; } public Course Course { get; set; } public Student Student { get; set; } } ``` ####创建数据库上下文 使得给定的数据模型与 Entity Framework 功能相协调的主类是数据库上下文类。 可以通过继承 Microsoft.EntityFrameworkCore.DbContext 类的方式创建此类。 在该类中你可以指定数据模型中包含哪些实体 ``` 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; } } ``` 当数据库创建完成后, EF 创建一系列数据表,表名默认和 DbSet 属性名相同。 集合属性的名称一般使用复数形式,但不同的开发人员的命名习惯可能不一样,开发人员根据自己的情况确定是否使用复数形式 ``` 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"); } } ``` ####注册 SchoolContext ASP.NET Core 默认实现 依赖注入。 在应用程序启动过程通过依赖注入注册相关服务 (例如 EF 数据库上下文) ``` services.AddDbContext<SchoolContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"))); ``` 打开 appsettings.json 文件,并按以下所示添加连接字符串。 ``` { "ConnectionStrings": { "SchoolContext": "Server=.;Database=SchoolContext;uid=sa;password=123456", "SchoolContext2": "Server=(localdb)\\mssqllocaldb;Database=SchoolContext;Trusted_Connection=True; MultipleActiveResultSets=true" } } ``` 数据库连接字符串可以使用指定使用 SQL Server LocalDB 数据库。 LocalDB 是 SQL Server Express 数据库引擎的轻量级版本,用于应用程序开发,不在生产环境中使用。 LocalDB 作为按需启动并在用户模式下运行的轻量级数据库没有复杂的配置。 默认情况下, LocalDB 在 C:/Users/目录下创建 .mdf 数据库文件。 ####初始化数据库 ``` public static class DbInitializer { public static void Initialize(SchoolContext context) { var isscuess = 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(); } } ``` 在 Program.cs,修改 Main 方法,使得在应用程序启动时能执行以下操作: ``` using ContosoUniversity.Data; using Microsoft.Extensions.DependencyInjection; using Microsoft.AspNetCore.Hosting; using Microsoft.Extensions.Hosting; using Microsoft.Extensions.Logging; using System; namespace ContosoUniversity { public class Program { public static void Main(string[] args) { var host = CreateHostBuilder(args).Build(); CreateDbIfNotExists(host); host.Run(); } private static void CreateDbIfNotExists(IHost host) { using (var scope = host.Services.CreateScope()) { var services = scope.ServiceProvider; try { var context = services.GetRequiredService<SchoolContext>(); DbInitializer.Initialize(context); } catch (Exception ex) { var logger = services.GetRequiredService<ILogger<Program>>(); logger.LogError(ex, "An error occurred creating the DB."); } } } public static IHostBuilder CreateHostBuilder(string[] args) => Host.CreateDefaultBuilder(args) .ConfigureWebHostDefaults(webBuilder => { webBuilder.UseStartup<Startup>(); }); } } ``` ####EF CORE读取数据 我们这里可以使用异步的方式来读取与返回数据 ``` public async Task<IActionResult> Index() { return View(await _context.Students.ToListAsync()); } ``` view页面中razor解析数据 ``` @model IEnumerable<Learn.Models.Student> @{ ViewData["Title"] = "Index"; } <h1>Index</h1> <form> <p> <a asp-action="Create">Create New</a> <input type="text" name="firstMidName" value="@ViewBag.firstMidName" /> <input type="submit" value="查询" /> </p> </form> <table class="table"> <thead> <tr> <th> @Html.DisplayNameFor(model => model.LastName) </th> <th> @Html.DisplayNameFor(model => model.FirstMidName) </th> <th> @Html.DisplayNameFor(model => model.EnrollmentDate) </th> <th></th> </tr> </thead> <tbody> @foreach (var item in Model) { <tr> <td> @Html.DisplayFor(modelItem => item.LastName) </td> <td> @Html.DisplayFor(modelItem => item.FirstMidName) </td> <td> @Html.DisplayFor(modelItem => item.EnrollmentDate) </td> <td> <a asp-action="Edit" asp-route-id="@item.ID">Edit</a> | <a asp-action="Details" asp-route-id="@item.ID">Details</a> | <a asp-action="Delete" asp-route-id="@item.ID">Delete</a> </td> </tr> } </tbody> </table> ```
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