IQuerable与IEnumable的区别

namespace System.Linq
{
    public interface IQueryable : IEnumerable
    {
        Type ElementType { get; }
        Expression Expression { get; }
        IQueryProvider Provider { get; }
    }
}

            //linq 表达式的返回值的类型是IQueryable
            IQueryable<HKSJ_USERS> temp = from u in dbContext.HKSJ_USERS
                       where u.ID > 4
                       select u;
            //初始化了一下IQueryable接口里面的三个参数作用：
            // 1 linq表达式转成表达式树Expression
            // 2 给元素类型 Type ElementType赋值，这里指的是<HKSJ_USERS>
            // 3 给提供者IQueryProvider Provider赋值，这里是efProvider，若是XML那就是xmlProvider，若是string 就stringProvider
　　　　　　　　 所以理论上linq可以无限扩展。

            //当用到 IQueryable接口的集合的数据的时候，provider解析Expression然后获取相应的数据。进行遍历执行。
            //linq to ef:查询是在数据库端进行过滤。
            foreach (var hksjUsers in temp)
            {
                Console.WriteLine(hksjUsers.ID + " " + hksjUsers.UserName);
            }

            //IEnumable内存里面过滤：把数据库中的所有的数据都查询到程序里面来之后，再进行过滤。
         //linq  to object
            var demoList = from u in dbContext.HKSJ_USERS.AsIEnumable() //ToList()
                           where u.ID > 4
                           select u;
            foreach (var hksjUsers in demoList)
            {
                
            }
　　　　　　　

         //List集合、Arrary，Dictionary，....都继承与IEnumable接口。

namespace System.Collections
{
    //
    // 摘要:
    //     Exposes an enumerator, which supports a simple iteration over a non-generic collection.To
    //     browse the .NET Framework source code for this type, see the Reference Source.
    [ComVisible(true)]
    [Guid("496B0ABE-CDEE-11d3-88E8-00902754C43A")]
    public interface IEnumerable
    {
        //
        // 摘要:
        //     Returns an enumerator that iterates through a collection.
        //
        // 返回结果:
        //     An System.Collections.IEnumerator object that can be used to iterate through
        //     the collection.
        [DispId(-4)]
        IEnumerator GetEnumerator();
    }
}

namespace System.Collections
{
    //
    // 摘要:
    //     Supports a simple iteration over a non-generic collection.
    [ComVisible(true)]
    [Guid("496B0ABF-CDEE-11d3-88E8-00902754C43A")]
    public interface IEnumerator
    {
        //
        // 摘要:
        //     Gets the current element in the collection.
        //
        // 返回结果:
        //     The current element in the collection.
        object Current { get; }

        //
        // 摘要:
        //     Advances the enumerator to the next element of the collection.
        //
        // 返回结果:
        //     true if the enumerator was successfully advanced to the next element; false if
        //     the enumerator has passed the end of the collection.
        //
        // 异常:
        //   T:System.InvalidOperationException:
        //     The collection was modified after the enumerator was created.
        bool MoveNext();
        //
        // 摘要:
        //     Sets the enumerator to its initial position, which is before the first element
        //     in the collection.
        //
        // 异常:
        //   T:System.InvalidOperationException:
        //     The collection was modified after the enumerator was created.
        void Reset();
    }
}