实体框架的子查询 [英] Subquery with Entity Framework
问题描述
我要将子系统从 NHibernate 移植到 Entity Framework ，并希望了解将以下查询移植到 EF 的最佳方法.
I'm porting a subsystem from NHibernate to Entity Framework and want to see the best way to port the following query to EF.
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();
帐户余额类别为:
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; }
}
表为:
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
)
)
样本数据是(使用数字ID以便更好地理解):
A sample data is (using numeric ids for better understanding):
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
AccountBalanceByDate 实体在特定日期保留帐户余额.如果某天没有交易，则该天将没有 AccountBalanceByDate ，我们应该查找前几天以查看该帐户的余额.
The AccountBalanceByDate entity hold the account balance in a specific day. If a day doesn't have a transaction, that day will not have an AccountBalanceByDate and we should look for the previous days to see the balance for that account.
如果我查询日期为 2014-02-01 ，我应该得到:
If I query with the date 2014-02-01 I should get:
No results
如果我查询日期为 2014-02-02 ，我应该得到:
If I query with the date 2014-02-02 I should get:
1 | 2014-02-01 | 101 | 1390.00000
2 | 2014-02-01 | 102 | 1360.00000
3 | 2014-02-01 | 103 | 1630.00000
如果我查询日期为 2014-02-03 ，我应该得到:
If I query with the date 2014-02-03 I should get:
1 | 2014-02-01 | 101 | 1390.00000
4 | 2014-02-02 | 102 | 1370.00000
5 | 2014-02-02 | 103 | 1700.00000
如果我查询日期为 2014-02-04 ，我应该得到:
If I query with the date 2014-02-04 I should get:
4 | 2014-02-02 | 102 | 1370.00000
6 | 2014-02-03 | 101 | 1490.00000
7 | 2014-02-03 | 103 | 1760.00000
如果我查询日期为 2014-02-05 ，我应该得到:
If I query with the date 2014-02-05 I should get:
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，但这并不理想.
I can do this in Entity Framework using raw SQL, but it is not the ideal.
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();
}
最好仅一次访问数据库，就像在 NHibernate 和原始SQL中一样，但是仅使用 linq ，有可能吗?
It is preferred to go to database just one time, like in NHibernate and raw SQL, but using just linq, is it possible?
更新:
修正问题后的结果.
SQL显示有关GIST的示例查询: https://gist.github.com/LawfulHacker/275ec363070f2513b887
SQL showing the sample query on GIST: https://gist.github.com/LawfulHacker/275ec363070f2513b887
GIST上的实体框架示例: https://gist.github.com/LawfulHacker/9f7bd31a21363ee0b646
Entity Framework sample on GIST: https://gist.github.com/LawfulHacker/9f7bd31a21363ee0b646
推荐答案
以下查询仅对数据库执行一次查询即可完全满足我的需要:
The following query do exactly what I need with just one query to the database:
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.
Thanks @AgentShark for the help.
代码在GIST上: https://gist.github.com/LawfulHacker/9f7bd31a21363ee0b646
这篇关于实体框架的子查询的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
