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【EF】EF框架 Code First Fluent API
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：
【EF】EF框架 Code First Fluent API
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