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ctx.Configuration.LazyLoadingEnabled=false;

using (var ctx = new SchoolDBEntities())
    {
        //Loading students only
        IList<Student> studList = ctx.Students.ToList<Student>();

        Student std = studList[0];

        //Loads Student address for particular Student only (seperate SQL query)
        StudentAddress add = std.StudentAddress;
    }

using (var context = new SchoolDBEntities())
{
    //Disable Lazy loading
    context.Configuration.LazyLoadingEnabled = false;
                
    var student = (from s in context.Students
                        where s.StudentName == "Bill"
                        select s).FirstOrDefault<Student>();

    context.Entry(student).Reference(s => s.Standard).Load();
}     

// Loading Method Lazy Loading的意思就是不加在关联数据，ToList过的表就不用延迟加载了，
// 因为已经全部在内存中了ExplicitLoading就是当Lazy Loading关闭了，还是可以再加载关联的数据，
// 不过是需要显示的声明Eager Loading使用Include方法关联预先加载的实体Include()，两表必须含有外键关系，
// 只需要指定键名对应的类属性名即可，不需指定结果字段（即全部映射）。默认搜索某表时，不会顺带查询外键表，
// 直到真正使用时才会再读取数据库查询；若是使用 Include()，则会在读取本表时把指定的外键表信息也读出来。

using (var ctx = new SchoolDBEntities())
        {
            stud = ctx.Students.Include("Standard")
                               .Where(s => s.StudentName == "Student1").FirstOrDefault<Student>();
           
        }
        
//////////////////////////////////////////////////////////////////////////////////
using System;
using System.Data.Entity; 
   
class Program
{
    static void Main(string[] args)
    {
    
        using (var ctx = new SchoolDBEntities())
        {
            stud = ctx.Students.Include(s => s.Standard)
                                .Where(s => s.StudentName == "Student1")
                                .FirstOrDefault<Student>();
           
        }
    }
}

/////////////////////////////////////////////////////////////////////
using (var ctx = new SchoolDBEntities())
    {
        stud = ctx.Students.Include(s => s.Standard.Teachers)
                            .Where(s => s.StudentName == "Student1")
                            .FirstOrDefault<Student>();
    }