灵感来自于此我做了这个:
ISortable
public interface ISortable<T>
{
IPageable<T> OrderBy<U>(Expression<Func<T, U>> orderBy);
IPageable<T> OrderByDescending<U>(Expression<Func<T, U>> orderBy);
}
IPageable
public interface IPageable<T> : ISortable<T>, IEnumerable<T>
{
IPageable<T> Page(int pageNumber, int pageSize);
List<T> ToList();
int TotalPages { get; }
int TotalItemCount { get; }
int PageNumber { get; }
int? PageSize { get; }
}
分页
public class Pageable<T> : IPageable<T>
{
private readonly IQueryable<T> _countQuery;
private IQueryable<T> _sourceQuery;
/// <summary>
/// A pageable result
/// </summary>
/// <param name="sourceQuery">Query which holdes all relevant items.</param>
public Pageable(IQueryable<T> sourceQuery)
{
_sourceQuery = sourceQuery;
_countQuery = sourceQuery;
PageNumber = 1;
}
/// <summary>
/// A pageable result
/// </summary>
/// <param name="sourceQuery">Query which holdes all relevant items.</param>
/// <param name="countQuery">
/// Alternative query optimized for counting.
/// <see cref="countQuery"/> is required to give the same count as <see cref="sourceQuery"/> else paging will break.
/// <remarks>No checks if <see cref="sourceQuery"/> and <see cref="countQuery"/> return the same count are appiled.</remarks>
/// </param>
public Pageable(IQueryable<T> sourceQuery, IQueryable<T> countQuery)
: this (sourceQuery)
{
_countQuery = countQuery;
}
#region Implementation of IEnumerable
/// <summary>
/// Returns an enumerator that iterates through the collection.
/// </summary>
/// <returns>
/// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
/// </returns>
/// <filterpriority>1</filterpriority>
public IEnumerator<T> GetEnumerator()
{
return _sourceQuery.GetEnumerator();
}
/// <summary>
/// Returns an enumerator that iterates through a collection.
/// </summary>
/// <returns>
/// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
/// </returns>
/// <filterpriority>2</filterpriority>
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
#endregion
#region Implementation of ISortable
public IPageable<T> OrderBy<U>(Expression<Func<T, U>> orderBy)
{
_sourceQuery = _sourceQuery.OrderBy(orderBy);
return this;
}
public IPageable<T> OrderByDescending<U>(Expression<Func<T, U>> orderBy)
{
_sourceQuery = _sourceQuery.OrderByDescending(orderBy);
return this;
}
#endregion
#region Implementation of IPageable
public int PageNumber { get; private set; }
public int? PageSize { get; private set; }
public int TotalItemCount
{
get { return _countQuery.Count(); }
}
public int TotalPages
{
get { return (int) (Math.Ceiling((double) TotalItemCount/PageSize ?? 1)); }
}
/// <summary>
/// Chop a query result into pages.
/// </summary>
/// <param name="pageNumber">Page number to fetch. Starting from 1.</param>
/// <param name="pageSize">Items per page.</param>
/// <returns></returns>
public IPageable<T> Page(int pageNumber, int pageSize)
{
PageNumber = pageNumber;
PageSize = pageSize;
_sourceQuery = _sourceQuery
.Skip((pageNumber - 1) * pageSize)
.Take(pageSize);
return this;
}
public List<T> ToList()
{
return _sourceQuery.ToList();
}
#endregion
}
以上工作.巨大的成功!:)
但是我遇到了实现该方法的问题.ThenBy().问题是.ThenBy()只有在.OrderBy()被调用时才能访问.
我注意到IQueryable.OrderBy返回一个IOrderedQueryable,这就是访问的.ThenBy()来源.但是为了使我当前的解决方案工作,我需要制作一个IOrderedPageable和一个新的OrderedPagable.OrderedPagable几乎就是Pageable的副本,这真的是非常糟糕的设计.
我非常怀疑它是如何在LINQ中完成的.所以我的问题是,他们是怎么做到的？我很好奇 :)
我注意到的一件事是,几乎所有LINQ方法都是扩展方法,是"技巧"的一部分:)？
听起来你的类OrderedPageable可能是一个子类,Pageable并另外实现IOrderedPageable接口.
继承方法似乎有意义,因为处理的任何东西都Pageable应该能够以OrderedPageable相同的方式处理.
通过稍微更改接口并使用类似于上面的接口继承方法,您可以使用不可变的可查询类和扩展方法来实现您正在寻找的功能.
在我看来,使用更清晰,更符合LINQ.
例子:
query.AsPageable(100).Page(1);
query.AsPageable(100).OrderBy(x => x.Name).ThenBy(x => x.Age).Page(1).ToList();
我没有测试过这个,但这个概念应该有效.注意:
SourceQuery属性,因为您的查询提供程序可能无法成功地针对此新类型转换查询.IPageableQueryPageableExtensionsPageableQuery接口:
public interface IPageableQuery<T> : IQueryable<T>
{
int TotalPages { get; }
int TotalItemCount { get; }
int PageSize { get; }
}
public interface IOrderedPageableQuery<T> : IPageableQuery<T>, IOrderedQueryable<T>
{
}
实现:
public class PageableQuery<T> : IPageableQuery<T>
{
readonly IQueryable<T> _sourceQuery;
readonly Lazy<int> _totalItemCount;
public int TotalPages { get { return (int)Math.Ceiling((double)TotalItemCount / PageSize); } }
public int TotalItemCount { get { return _totalItemCount.Value; } }
public int PageSize { get; private set; }
public PageableQuery(IQueryable<T> sourceQuery, int pageSize)
{
_sourceQuery = sourceQuery;
_totalItemCount = new Lazy<int>(() => _sourceQuery.Count());
PageSize = pageSize;
}
public IEnumerator<T> GetEnumerator() { return _sourceQuery.GetEnumerator();}
IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); }
public Expression Expression { get { return _sourceQuery.Expression; } }
public Type ElementType { get { return _sourceQuery.ElementType; } }
public IQueryProvider Provider { get { return _sourceQuery.Provider; } }
}
public class OrderedPageableQuery<T> : IOrderedPageableQuery<T>
{
readonly IPageableQuery<T> _sourcePageableQuery;
readonly IOrderedQueryable<T> _sourceQuery;
public int TotalPages { get { return (int)Math.Ceiling((double)TotalItemCount / PageSize); } }
public int TotalItemCount { get { return _sourcePageableQuery.TotalItemCount; } }
public int PageSize { get { return _sourcePageableQuery.PageSize; } }
public OrderedPageableQuery(IPageableQuery<T> sourcePageableQuery, IOrderedQueryable<T> newSourceQuery)
{
_sourcePageableQuery = sourcePageableQuery;
_sourceQuery = newSourceQuery;
}
public IEnumerator<T> GetEnumerator() { return _sourceQuery.GetEnumerator();}
IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); }
public Expression Expression { get { return _sourceQuery.Expression; } }
public Type ElementType { get { return _sourceQuery.ElementType; } }
public IQueryProvider Provider { get { return _sourceQuery.Provider; } }
}
扩展方法:
public static class PageableExtension
{
public static IPageableQuery<T> AsPageable<T>(this IQueryable<T> sourceQuery, int pageSize)
{
return new PageableQuery<T>(sourceQuery, pageSize);
}
public static IOrderedPageableQuery<T> OrderBy<T, U>(this IPageableQuery<T> sourcePageableQuery, Expression<Func<T, U>> orderBy)
{
return new OrderedPageableQuery<T>(sourcePageableQuery, Queryable.OrderBy(sourcePageableQuery, orderBy));
}
public static IOrderedPageableQuery<T> OrderByDescending<T, U>(this IPageableQuery<T> sourcePageableQuery, Expression<Func<T, U>> orderBy)
{
return new OrderedPageableQuery<T>(sourcePageableQuery, Queryable.OrderByDescending(sourcePageableQuery, orderBy));
}
public static IOrderedPageableQuery<T> ThenBy<T, U>(this IOrderedPageableQuery<T> sourcePageableQuery, Expression<Func<T, U>> orderBy)
{
return new OrderedPageableQuery<T>(sourcePageableQuery, Queryable.ThenBy(sourcePageableQuery, orderBy));
}
public static IOrderedPageableQuery<T> ThenByDescending<T, U>(this IOrderedPageableQuery<T> sourcePageableQuery, Expression<Func<T, U>> orderBy)
{
return new OrderedPageableQuery<T>(sourcePageableQuery, Queryable.ThenByDescending(sourcePageableQuery, orderBy));
}
public static IQueryable<T> Page<T>(this IPageableQuery<T> sourceQuery, int pageNumber)
{
return sourceQuery.Skip((pageNumber - 1) * sourceQuery.PageSize)
.Take(sourceQuery.PageSize);
}
}