之前我们配置的实体都都在OnModelCreating方法中，如果有很多实体的话，OnModelCreating方法管理很麻烦

我们可以用单独的类来管理配置，继承EntityTypeConfiguration<TEntity>类实现

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public class StudentEntityConfiguration: EntityTypeConfiguration<Student>
{
    public StudentEntityConfiguration()
    {
        
            this.ToTable("StudentInfo");
                
            this.HasKey<int>(s => s.StudentKey);
                
                
            this.Property(p => p.DateOfBirth)
                    .HasColumnName("DoB")
                    .HasColumnOrder(3)
                    .HasColumnType("datetime2");

            this.Property(p => p.StudentName)
                    .HasMaxLength(50);
                        
            this.Property(p => p.StudentName)
                    .IsConcurrencyToken();
                
            this.HasMany<Course>(s => s.Courses)
                .WithMany(c => c.Students)
                .Map(cs =>
                        {
                            cs.MapLeftKey("StudentId");
                            cs.MapRightKey("CourseId");
                            cs.ToTable("StudentCourse");
                        });
    }
}
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public class SchoolDBContext: DbContext 
{
    public SchoolDBContext(): base() 
    {
    }

    public DbSet<Student> Students { get; set; }
    public DbSet<Standard> Standards { get; set; }
    public DbSet<StudentAddress> StudentAddress { get; set; }
        
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
            // Moved all Student related configuration to StudentEntityConfiguration class
            modelBuilder.Configurations.Add(new StudentEntityConfiguration());
               
    }
}