Question

我在NHibernate 3.2和SQLite提供程序中有这个简单的linq查询：

var all = (from book in Session.Query<Book>() select book)
    .Skip(15)
    .Take(15)                
    .ToList();

此查询正确返回15个实体，但是当我尝试使用FetchMany等依赖加载依赖集合时：

var all = (from book in Session.Query<Book>() select book)
    .FetchMany(books => books.Authors)
    .Skip(15)
    .Take(15)                
    .ToList();

我只返回了11个实体。这是一个我还缺少的错误吗？

以下是生成的SQL查询

select
     book0_.Id as Id2_0_,
     author2_.Id as Id0_1_,
     book0_.Title as Title2_0_,
     book0_.Sort as Sort2_0_,
     book0_.TimeStamp as TimeStamp2_0_,
     book0_.PubDate as PubDate2_0_,
     book0_.Series_Index as Series6_2_0_,
     book0_.Author_Sort as Author7_2_0_,
     book0_.Isbn as Isbn2_0_,
     book0_.Lccn as Lccn2_0_,
     book0_.Path as Path2_0_,
     book0_.Flags as Flags2_0_,
     book0_.Uuid as Uuid2_0_,
     book0_.Has_Cover as Has13_2_0_,
     book0_.Last_Modified as Last14_2_0_,
     author2_.Name as Name0_1_,
     author2_.Sort as Sort0_1_,
     author2_.Link as Link0_1_,
     authors1_.book as book0__,
     authors1_.author as author0__
from 
    books book0_ 
  left outer join 
    books_authors_link authors1_ on book0_.Id=authors1_.book left outer join authors author2_ 
  on authors1_.author=author2_.Id
order by book0_.Id asc
limit 15 /* @p0 */ offset 0 /* @p1 */

这有效地将结果集限制为15行而不是我想要的15个实体。

Answer 1

skip和take被转换为sql中限制行的等价物，因为你很想用连接获取，所以你无能为力。

渴望获取您需要的前15本书：

var all = Session.Query<Book>()
    .Skip(15)
    .Take(15)                
    .ToList();

var ids = all.Select(b => b.Id).ToList();

// fetch all Authors of the books, now the books in all have initialized Authors
Session.Query<Book>()
    .Where(b => ids.Contains(b.Id))
    .FetchMany(books => books.Authors)
    .List();

这有2次往返

更新：使用QueryOver进行一次往返，也许您可以转换为Linq

var subquery = QueryOver.Of<Book>()
    .Skip(15)
    .Take(15)
    .Select(b => b.Id);

var all = Session.QueryOver<Book>()
    .WithSubquery.WhereProperty(b => b.Id).In(subquery)
    .Fetch(books => books.Authors).Eager
    .ToList();

Answer 2

var data = session.QueryOver<EmployeeDetails>()
                                  .Where(x => x.Salary > 2000)
                                  //.Take(2)
                                  .Skip(2)
                                  .Take(2)
                                  .List();
                //if take is before skip then it will skip the last (mentioned digits) rows
                //if take is after skip then it will skip the first (mentioned digits) rows

NHibernate Linq提供者和take（）skip（）以及渴望获取

2 个答案: