具有实体框架的子查询

Question

我正在将子系统从NHibernate移植到Entity Framework,并希望看到将以下查询移植到EF的最佳方法.

var date = DateTime.Now; // It can be any day
AccountBalanceByDate abbd = null;
var lastBalanceDateByAccountQuery = QueryOver.Of<AccountBalanceByDate>()
    .Where(x => x.AccountId == abbd.AccountId && x.Date < date)
    .Select(Projections.Max<AccountBalanceByDate>(x => x.Date));

var lastBalances = session.QueryOver<AccountBalanceByDate>(() => abbd)
    .WithSubquery.WhereProperty(x => x.Date).Eq(lastBalanceDateByAccountQuery)
    .List();

帐户余额类是:

public class AccountBalanceByDate
{
    public virtual int Id { get; set; }
    public virtual int AccountId { get; set; }
    public virtual DateTime Date { get; set; }
    public virtual decimal Balance { get; set; }
}

该表是:

CREATE TABLE [dbo].[AccountBalanceByDate]
(
    [Id]        int NOT NULL,
    [AccountId] int NOT NULL,
    [Date]      [datetime] NOT NULL,
    [Balance]   [decimal](19, 5) NOT NULL,

    PRIMARY KEY CLUSTERED 
    (
        [Id] ASC
    )
)

示例数据是(使用数字ID以便更好地理解):

Id | Date        | Account | Balance
------------------------------------
 1 | 2014-02-01  | 101     | 1390.00000
 2 | 2014-02-01  | 102     | 1360.00000
 3 | 2014-02-01  | 103     | 1630.00000
 4 | 2014-02-02  | 102     | 1370.00000
 5 | 2014-02-02  | 103     | 1700.00000
 6 | 2014-02-03  | 101     | 1490.00000
 7 | 2014-02-03  | 103     | 1760.00000
 8 | 2014-02-04  | 101     | 1530.00000
 9 | 2014-02-04  | 102     | 1540.00000

该AccountBalanceByDate实体持有某一天的账户余额.如果一天没有交易,那一天将没有AccountBalanceByDate,我们应该查看前几天查看该帐户的余额.

如果我查询日期2014-02-01我应该得到:

 No results

如果我查询日期2014-02-02我应该得到:

 1 | 2014-02-01  | 101     | 1390.00000
 2 | 2014-02-01  | 102     | 1360.00000
 3 | 2014-02-01  | 103     | 1630.00000

如果我查询日期2014-02-03我应该得到:

 1 | 2014-02-01  | 101     | 1390.00000
 4 | 2014-02-02  | 102     | 1370.00000
 5 | 2014-02-02  | 103     | 1700.00000

如果我查询日期2014-02-04我应该得到:

 4 | 2014-02-02  | 102     | 1370.00000
 6 | 2014-02-03  | 101     | 1490.00000
 7 | 2014-02-03  | 103     | 1760.00000

如果我查询日期2014-02-05我应该得到:

 7 | 2014-02-03  | 103     | 1760.00000
 8 | 2014-02-04  | 101     | 1530.00000
 9 | 2014-02-04  | 102     | 1540.00000

我可以使用原始SQL在Entity Framework中执行此操作,但它不是理想的.

using (var context = new DbContext()) 
{ 
    var lastBalances = context.AccountBalanceByDate.SqlQuery(
        @"SELECT
            *
        FROM 
            [AccountBalanceByDate] AB
        WHERE
            DATE = (
                SELECT
                    MAX(Date) 
                FROM 
                    [AccountBalanceByDate]
                WHERE
                    AccountId = AB.AccountId AND DATE < @p0
            )", date).ToList(); 
}

最好只去一次数据库,比如NHibernate和原始SQL,但只使用linq,是否可能？

更新:

修复了问题的结果.

SQL在GIST上显示示例查询:https://gist.github.com/LawfulHacker/275ec363070f2513b887

GIST上的实体框架示例:https://gist.github.com/LawfulHacker/9f7bd31a21363ee0b646

Answer 1

以下查询只需要对数据库进行一次查询即可完成所需:

var accountBalance = context
    .AccountBalanceByDate
    .Where(a => 
        a.Date == context.AccountBalanceByDate
             .Where(b => b.AccountId == a.AccountId && b.Date < date).Max(b => b.Date));

感谢@AgentShark的帮助.

代码在GIST上:https://gist.github.com/LawfulHacker/9f7bd31a21363ee0b646