FluentAPI

1、使用FluentAPI

1.1、在OnModelCreating方法下使用

    public class FluentApiDb:DbContext
    {
        public DbSet<Course> Courses { get; set; }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Course>().Property(o => o.Title).HasMaxLength(20);
        }
    }

1.1、新增一个类，在OnModelCreating中引用

     public class FluentApiDb:DbContext
    {
        public DbSet<Teacher> Teacher { get; set; }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Configurations.Add(new TeacherMap());
            modelBuilder.Configurations.Add(new StudentMap());
            base.OnModelCreating(modelBuilder);
        }
    }

通过反射动态加入。利：自动加入，无需人工反复加；弊：影响性能。

  public class FluentApiDb:DbContext
    {
        public DbSet<Teacher> Teacher { get; set; }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
             var typesToRegister = Assembly.GetExecutingAssembly().GetTypes()
               .Where(type => !String.IsNullOrEmpty(type.Namespace))
               .Where(type => type.BaseType != null && type.BaseType.IsGenericType
                    && type.BaseType.GetGenericTypeDefinition() == typeof(EntityTypeConfiguration<>));
                foreach (var type in typesToRegister)
                {
                    dynamic configurationInstance = Activator.CreateInstance(type);
                    modelBuilder.Configurations.Add(configurationInstance);
                }

            base.OnModelCreating(modelBuilder);
        }
    }

2、FluentAPI详细用法

• 设置主键
  modelBuilder.Entity<x>().HasKey(t => t.Name);
• 设置联合主键
  modelBuilder.Entity<x>().HasKey(t =>new{t.Name,t.ID} );
• 取消数据库字段标识（取消自动增长）
  modelBuilder.Entity<x>().Property(t=>t.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);
• 设置数据库字段标识（自动增长）
  modelBuilder.Entity<Teacher>().Property(t =>t.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
• 设置字段最大长度
  modelBuilder.Entity<ClassA>().Property(t => t.Name).HasMaxLength(100);
• 设置字段为必需
  modelBuilder.Entity<ClassA>().Property(t =>t.Id).IsRequired();
• 属性不映射到数据库
  modelBuilder.Entity<ClassA>().Ignore(t => t.A);
• 将属性指定数据库列名：
  modelBuilder.Entity<ClassA>() .Property(t => t.A) .HasColumnName("A_a");
• 级联删除（数据库默认是不级联删除的）
  modelBuilder.Entity<Course>().HasRequired(t => t.Department).WithMany(t => t.Courses).HasForeignKey(d => d.DepartmentID).WillCascadeOnDelete();
• 设置为Timestamp
  modelBuilder.Entity<OfficeAssignment>() .Property(t => t.Timestamp) .IsRowVersion();
• 表1对0..1(Instructor实体可以包含零个或一个OfficeAssignment)
  modelBuilder.Entity<OfficeAssignment>().HasRequired(t => t.Instructor).WithOptional(t => t.OfficeAssignment);
• 表1对1
  modelBuilder.Entity<Instructor>().HasRequired(t => t.OfficeAssignment).WithRequiredPrincipal(t => t.Instructor);
• 表1对n（Department为主表）
  modelBuilder.Entity<Staff>() .HasRequired(c => c.Department) .WithMany(t => t.Staffs)
• 指定外键名（指定表Staff中的字段DepartmentID为外键）
  modelBuilder.Entity<Staff>() .HasRequired(c => c.Department) .WithMany(t => t.Staffs) .Map(m => m.MapKey("DepartmentID"));
• 表n对n
  modelBuilder.Entity<Course>()
  .HasMany(t => t.Instructors)
  .WithMany(t => t.Courses)
• 表n对n指定连接表名及列名
  modelBuilder.Entity<Course>()
  .HasMany(t => t.Instructors)
  .WithMany(t => t.Courses)
  .Map(m =>
  {
  m.ToTable("CourseInstructor");
  m.MapLeftKey("CourseID");
  m.MapRightKey("InstructorID");
  });