在Code First方法中，还可以通过Fluent API的方式来处理实体与数据表之间的映射关系。
要使用Fluent API必须在构造自定义的DbContext时，重写OnModelCreating方法，在此方法体内调用Fluent API。
如下面代码所示：
public class BlogDbContext : DbContext
{
public BlogDbContext()
: base("name=BlogDB2005")
{
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
//do something
base.OnModelCreating(modelBuilder);
}
}
下面来看一些简单的例子
主键
modelBuilder.Entity<BlogUser>().HasKey(user => user.UserId);
联合主键
//联合主键
modelBuilder.Entity<BlogUser>().HasKey(user => new { user.UserId, user.BlogName });
字段非空
//要求属性必填 modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).IsRequired();
设定字段最大长度
modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).HasMaxLength(20);
设置复杂属性，相当数据特性中的ComplexType
modelBuilder.ComplexType<Address>();
属性字段不映射到数据表字段，相当于数据特性中的NotMapped
modelBuilder.Entity<BlogUser>().Ignore(user => user.MyProperty);
设置字段是否自动增长
//设置自动增长，如不需要自动增长，则设为 DatabaseGeneratedOption.None
modelBuilder.Entity<BlogUser>().Property(user => user.UserId)
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
设置外键
///产生一对多的关系
modelBuilder.Entity<Post>()
.HasRequired(p =>p.BlogUser)
.WithMany(user => user.Posts)
.HasForeignKey(p => p.UserId);
///与上面等效
//modelBuilder.Entity<BlogUser>()
// .HasMany(user => user.Posts)
// .WithRequired(p => p.BlogUser)
// .HasForeignKey(p => p.UserId);
设定实体映射到数据库中的表名
modelBuilder.Entity<BlogUser>().ToTable("MyUser");
设置实体属性映射到数据库中的列名
modelBuilder.Entity<BlogUser>()
.Property(user => user.Description)
.HasColumnName("userDescription")
.HasColumnType("ntext");
下面给出完整代码，方便测试：
1 class FluentAPISample
2 {
3
4 static void Main(string[] args)
5 {
6 using (var db = new BlogDbContext())
7 {
8 db.Database.Create();
9 }
10 }
11 }
12
13 public class BlogDbContext : DbContext
14 {
15 public BlogDbContext()
16 : base("name=BlogDB2005")
17 {
18 Database.SetInitializer<BlogDbContext>(
19 new DropCreateDatabaseIfModelChanges<BlogDbContext>()
20 );
21 }
22 protected override void OnModelCreating(DbModelBuilder modelBuilder)
23 {
24 modelBuilder.Entity<BlogUser>().HasKey(user => user.UserId);
25 //联合主键
26 //modelBuilder.Entity<BlogUser>().HasKey(user => new { user.UserId, user.BlogName });
27
28 //设置自动增长，如不需要自动增长，则设为 DatabaseGeneratedOption.None
29 modelBuilder.Entity<BlogUser>().Property(user => user.UserId)
30 .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
31
32 //要求属性必填
33 modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).IsRequired();
34 modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).HasMaxLength(20);
35 modelBuilder.Entity<BlogUser>().Ignore(user => user.MyProperty);
36
37 modelBuilder.ComplexType<Address>();
38
39 ///产生一对多的关系
40 modelBuilder.Entity<Post>()
41 .HasRequired(p =>p.BlogUser)
42 .WithMany(user => user.Posts)
43 .HasForeignKey(p => p.UserId);
44
45 ///与上面等效
46 //modelBuilder.Entity<BlogUser>()
47 // .HasMany(user => user.Posts)
48 // .WithRequired(p => p.BlogUser)
49 // .HasForeignKey(p => p.UserId);
50
51 modelBuilder.Entity<BlogUser>().ToTable("MyUser");
52
53 modelBuilder.Entity<BlogUser>()
54 .Property(user => user.Description)
55 .HasColumnName("userDescription")
56 .HasColumnType("ntext");
57
58 base.OnModelCreating(modelBuilder);
59 }
60 }
61
62 public partial class BlogUser
63 {
64 public int UserId { get; set; }
65 public string BlogName { get; set; }
66 public int MyProperty { get; set; }
67 public Address Address { get; set; }
68 public string Description { get; set; }
69 public virtual ICollection<Post> Posts { get; set; }
70 }
71 public partial class Post
72 {
73 public int PostId { get; set; }
74 public string PostTitle { get; set; }
75 public int UserId { get; set; }
76 public BlogUser BlogUser { get; set; }
77 }
78 public partial class Address
79 {
80 public string Province { get; set; }
81 public string City { get; set; }
82 }
1 class FluentAPISample
2 {
3
4 static void Main(string[] args)
5 {
6 using (var db = new BlogDbContext())
7 {
8 db.Database.Create();
9 }
10 }
11 }
12
13 public class BlogDbContext : DbContext
14 {
15 public BlogDbContext()
16 : base("name=BlogDB2005")
17 {
18 Database.SetInitializer<BlogDbContext>(
19 new DropCreateDatabaseIfModelChanges<BlogDbContext>()
20 );
21 }
22 protected override void OnModelCreating(DbModelBuilder modelBuilder)
23 {
24 modelBuilder.Entity<BlogUser>().HasKey(user => user.UserId);
25 //联合主键
26 //modelBuilder.Entity<BlogUser>().HasKey(user => new { user.UserId, user.BlogName });
27
28 //设置自动增长，如不需要自动增长，则设为 DatabaseGeneratedOption.None
29 modelBuilder.Entity<BlogUser>().Property(user => user.UserId)
30 .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
31
32 //要求属性必填
33 modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).IsRequired();
34 modelBuilder.Entity<BlogUser>().Property(user => user.BlogName).HasMaxLength(20);
35 modelBuilder.Entity<BlogUser>().Ignore(user => user.MyProperty);
36
37 modelBuilder.ComplexType<Address>();
38
39 ///产生一对多的关系
40 modelBuilder.Entity<Post>()
41 .HasRequired(p =>p.BlogUser)
42 .WithMany(user => user.Posts)
43 .HasForeignKey(p => p.UserId);
44
45 ///与上面等效
46 //modelBuilder.Entity<BlogUser>()
47 // .HasMany(user => user.Posts)
48 // .WithRequired(p => p.BlogUser)
49 // .HasForeignKey(p => p.UserId);
50
51 modelBuilder.Entity<BlogUser>().ToTable("MyUser");
52
53 modelBuilder.Entity<BlogUser>()
54 .Property(user => user.Description)
55 .HasColumnName("userDescription")
56 .HasColumnType("ntext");
57
58 base.OnModelCreating(modelBuilder);
59 }
60 }
61
62 public partial class BlogUser
63 {
64 public int UserId { get; set; }
65 public string BlogName { get; set; }
66 public int MyProperty { get; set; }
67 public Address Address { get; set; }
68 public string Description { get; set; }
69 public virtual ICollection<Post> Posts { get; set; }
70 }
71 public partial class Post
72 {
73 public int PostId { get; set; }
74 public string PostTitle { get; set; }
75 public int UserId { get; set; }
76 public BlogUser BlogUser { get; set; }
77 }
78 public partial class Address
79 {
80 public string Province { get; set; }
81 public string City { get; set; }
82 }
运行结果如下图示：
时间： 2025-01-06 18:42:25