《ASP.NET Core技术内幕与项目实战》精简集-EFCore2.2：基本使用（DbContext和迁移）

 1 //第一步：创建实体类
 2 //Book.cs
 3 public class Book
 4 {
 5     public long Id { get; set; }
 6     public string? Title { get; set; }
 7     public DateTime PubTime { get; set; }
 8     public double Price { get; set; }
 9     public string? AuthorName { get; set; }
10 }
11 
12 
13 //第二步：创建实体配置类，配置实体与数据表的映射关系
14 //BookConfig.cs
15 public class BookConfig : IEntityTypeConfiguration<Book>
16 {
17     public void Configure(EntityTypeBuilder<Book> builder)
18     {
19         builder.ToTable("T_Books");
20         builder.Property(x => x.Title).HasMaxLength(50).IsRequired();
21         builder.Property(x => x.AuthorName).HasMaxLength(20).IsRequired();
22     }
23 }
24 
25 
26 //第三步：创建DbContext的子类
27 public class TestDbContext: DbContext
28 {
29     public DbSet<Book> Books { get; set; }
30 
31     protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
32     {
33         string connStr = "Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=EFCoreDemo;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False;ApplicationIntent=ReadWrite;MultiSubnetFailover=False";
34         optionsBuilder.UseSqlServer(connStr);
35     }
36 
37     protected override void OnModelCreating(ModelBuilder modelBuilder)
38     {
39         base.OnModelCreating(modelBuilder);
40         modelBuilder.ApplyConfigurationsFromAssembly(this.GetType().Assembly);
41     }
42 }
43 
44 
45 //第四步：创建DbContext对象，通过ORM操作数据库，进行增删改查。Program.cs
46 using var ctx = new TestDbContext();
47 
48 //新增
49 var b1 = new Book
50 {
51     Title = "书名1",
52     AuthorName = "作者1",
53     Price = 59.8,
54     PubTime = new DateTime(2019, 3, 1)
55 };
56 var b2 = new Book
57 {
58     Title = "书名2",
59     AuthorName = "作者2",
60     Price = 49.8,
61     PubTime = new DateTime(2005, 3, 1)
62 };
63 var b3 = new Book
64 {
65     Title = "书名3",
66     AuthorName = "作者3",
67     Price = 39.8,
68     PubTime = new DateTime(2010, 3, 1)
69 };
70 ctx.Books.Add(b1);
71 ctx.Books.Add(b2);
72 ctx.Books.Add(b3);
73 await ctx.SaveChangesAsync();
74 
75 //查询
76 foreach (var b1 in ctx.Books.Where(b => b.Price > 40))
77 {
78     Console.WriteLine($"ID = {b1.Id}, Title = {b1.Title}, author = {b1.AuthorName}, price = {b1.Price}");
79 }
80 
81 //修改
82 var b2 = ctx.Books.Single(b => b.Id == 2);
83 b2.AuthorName = "作者XX";
84 await ctx.SaveChangesAsync();
85 
86 //删除
87 var b3 = ctx.Books.Single(b => b.Id == 3);
88 ctx.Books.Remove(b3); //也可以写成ctx.Remove(b3)
89 await ctx.SaveChangesAsync();

 1 //创建简单的三层应用：启动层（WebApi）、Domain层（类库）、EFCore层（类库）
 2 //三层引用关系：启动层引用Domain层和EFCore层、EFCore层引用Domain层
 3 
 4 
 5 //第一步：在Domain层创建Book实体
 6 //Book.cs
 7 public class Book
 8 {
 9     public long Id { get; set; }
10     public string? Title { get; set; }
11     public DateTime PubTime { get; set; }
12     public double Price { get; set; }
13     public string? AuthorName { get; set; }
14 }
15 
16 
17 //第二步：在EFCore层创建DbContext，配置映射关系
18 //BookStoreDbContext.cs
19 public class BookStoreDbContext: DbContext
20 {
21     public DbSet<Book> Books { get; set; }
22 
23     public BookStoreDbContext(DbContextOptions<BookStoreDbContext> options):base(options)
24     {
25 
26     }
27 
28     protected override void OnModelCreating(ModelBuilder builder)
29     {
30         base.OnModelCreating(builder);
31         builder.Entity<Book>(b => {
32             b.ToTable("T_Books");
33             b.Property(b => b.Title).HasMaxLength(50).IsRequired();
34             b.Property(b => b.AuthorName).HasMaxLength(20).IsRequired();
35         });
36     }
37 }
38 
39 
40 //第三步：启动层注册DbContext服务，并配置数据库连接字符串
41 //Program.cs
42 builder.Services.AddDbContext<BookStoreDbContext>(opt =>
43         {
44             string connStr = builder.Configuration.GetConnectionString("Default");
45             opt.UseSqlServer(connStr);
46         });
47 
48 
49 //第四步：在EFCore层创建IDesignTimeDbContextFactory<T>的实现类
50 //MyDesignTimeDbContextFactory.cs
51 public class MyDesignTimeDbContextFactory : IDesignTimeDbContextFactory<BookStoreDbContext>
52 {
53     public BookStoreDbContext CreateDbContext(string[] args)
54     {
55         DbContextOptionsBuilder<BookStoreDbContext> builder = new();
56         string connStr = "Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=BookStore;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False;ApplicationIntent=ReadWrite;MultiSubnetFailover=False";
57         builder.UseSqlServer(connStr);
58         return new BookStoreDbContext(builder.Options);
59     }
60 }
61 
62 
63 //第五步：在EFCore层，执行数据迁移，初始化数据库
64 Add-Migration initBookStore
65 Update-database
66 
67 
68 //第六步：在控制器中，以依赖注入的方式使用
69 ......
70 private readonly BookStoreDbContext ctx;
71 public TestController(BookStoreDbContext  ctx)
72 {
73     this.ctx = ctx;
74 }