我正在使用 EntityFramework Core 2.0 参与 Asp.NET Core 2.0 项目。
我正在尝试将现有的旧版 SQL 存储过程转换为 EntityFramework Core 中的 Linq，但我在处理 T-SQL 的这个特定部分时遇到了困难；
SET @Target = (SELECT MIN(A.[Serial])
FROM (SELECT [HighSerial] + 1 AS 'Serial'
FROM [Efn]
WHERE [Mid] = @Mid
AND ([HighSerial] + 1) BETWEEN @MinSerial AND @MaxSerial
AND ([HighSerial] + 1) NOT IN (SELECT [LowSerial]
FROM [Efn]
WHERE [Mid] = @Mid)) A)
我尝试通过 Linqer v4.6 运行它，但它基本上只是将相同的内容从 SQL 窗口传递到 Linq 窗口。
我在 Linqer 中将存储过程代码缩减为这样；
SELECT [HighSerial] + 1 AS 'Serial'
FROM [Efn]
WHERE [Mid] = @Mid
AND ([HighSerial] + 1) BETWEEN @MinSerial AND @MaxSerial
AND ([HighSerial] + 1) NOT IN (SELECT [LowSerial]
FROM [Efn]
WHERE [Mid] = @Mid)
Linqer 生成了我项目中的 Linq 代码，如下所示；
var query = from Efn in _serialNumberContext.Efns
where
Efn.Mid == mid &&
(Efn.HighSerial + 1) >= minSerial && (Efn.HighSerial + 1) <= maxSerial &&
!
(from Efn0 in _serialNumberContext.Efns
where
Efn0.Mid == mid
select new
{
Efn0.LowSerial
}).Contains(new { LowSerial = (Int64)(Efn.HighSerial + 1) })
select new
{
Serial = (Efn.HighSerial + 1)
};
但我无法弄清楚包装 T-SQL 代码的 Linq 翻译；
SET @Target = (SELECT MIN(A.[Serial])
FROM (
...
...
...) A)
如果有帮助，我提供了有关该项目的一些进一步详细信息；
Efn SQL Server Efn 表具有以下字段；
[Mid] INT NOT NULL,
[Date] DATE NOT NULL,
[LowSerial] BIGINT NOT NULL,
[HighSerial] BIGINT NOT NULL
在我的项目中，我有一个 Efn 实体类，如下所示；
public class Efn
{
[Required]
[Column(TypeName = "int")]
public int Mid { get; set; }
[Required]
[Column(TypeName="date")]
public DateTime Date { get; set; }
[Required]
[Column(TypeName = "bigint")]
public long LowSerial { get; set; }
[Required]
[Column(TypeName = "bigint")]
public long HighSerial { get; set; }
}
这是我的 dbcontext 类
公共(public)类 SerialNumberContext :DbContext {
public DbSet<Efn> Efns { get; set; }
public SerialNumberContext(DbContextOptions<SerialNumberContext> options) : base(options)
{
}
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Efn>()
.HasIndex(e => new { e.Mid, e.HighSerial, e.Date, e.LowSerial })
.IsUnique()
.HasName("IX_Efn_Mid_HighSerial_Date_LowSerial")
.ForSqlServerIsClustered();
modelBuilder.Entity<Efn>()
.HasIndex(e => new { e.Mid, e.LowSerial })
.HasName("IX_Efn_Mid_LowSerial");
base.OnModelCreating(modelBuilder);
}
}
这是完整的旧存储过程
USE [SerialNumberDB]
GO
IF EXISTS (SELECT 1 FROM sys.objects WHERE name = N'fetchEfnSerial' AND [type]=N'P')
BEGIN
DROP PROCEDURE [dbo].[fetchEfnSerial]
END
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER OFF
GO
CREATE PROCEDURE [dbo].[fetchEfnSerial]
(
@Mid INT,
@MinSerial BIGINT = NULL,
@MaxSerial BIGINT = NULL
)
AS
DECLARE @Date DATE = CONVERT(DATE, GETDATE())
DECLARE @Target BIGINT;
DECLARE @MAX_BIG_INT BIGINT = 9223372036854775807;
IF (@MinSerial IS NULL) BEGIN SET @MinSerial = 1 END
IF (@MaxSerial IS NULL) BEGIN SET @MaxSerial = @MAX_BIG_INT END
SET @Target = NULL;
BEGIN TRY
BEGIN TRANSACTION
IF ((SELECT 1
FROM [Efn]
WHERE @MinSerial BETWEEN [LowSerial] AND [HighSerial]
AND [Mid] = @Mid) IS NULL)
BEGIN
SET @Target = @MinSerial
END
ELSE
BEGIN
SET @Target = (SELECT MIN(A.[Serial])
FROM (SELECT [HighSerial] + 1 AS 'Serial'
FROM [Efn]
WHERE [Mid] = @Mid
AND ([HighSerial] + 1) BETWEEN @MinSerial AND @MaxSerial
AND ([HighSerial] + 1) NOT IN (SELECT [LowSerial]
FROM [Efn]
WHERE [Mid] = @Mid)) A)
END
IF @Target IS NULL
BEGIN
DECLARE @ErrorText VARCHAR(255) = 'ERROR: No Serial Numbers are available in the specified range; between MinSerial: ' + CONVERT(VARCHAR(19), @MinSerial)
+ ' and MaxSerial: ' + CONVERT(VARCHAR(19), @MaxSerial)
RAISERROR (@ErrorText, 16, 1)
END
IF @Target IS NOT NULL
BEGIN
IF EXISTS (SELECT 1
FROM [Efn]
WHERE [Mid] = @Mid AND [Date] = @Date
AND [HighSerial] = @Target - 1)
BEGIN
-- If for this MID, the max value in the serial number block before the target
-- serial number is from today, just update the max serial number of that block.
UPDATE [Efn]
SET [HighSerial] = @Target
WHERE [Mid] = @Mid
AND [HighSerial] = @Target - 1
END
ELSE
BEGIN
-- Otherwise, we need to make a new serial number block for this MID for today.
INSERT INTO [Efn]
SELECT @Mid, @Date, @Target, @Target
END
-- Return the target serial number to the caller so it can be used.
SELECT @Target AS 'Serial'
END
COMMIT TRANSACTION
END TRY
BEGIN CATCH
IF (@@TRANCOUNT > 0) ROLLBACK TRANSACTION
DECLARE @ERRORMSG NVARCHAR(255)
SET @ERRORMSG = ERROR_MESSAGE()
RAISERROR(@ERRORMSG, 16, 1)
END CATCH
GO
最佳答案
将 SQL 转换为 LINQ 查询理解:
- 将子选择转换为单独声明的变量。
- 按 LINQ 子句顺序转换每个子句，将一元运算符和聚合运算符(
DISTINCT、TOP、MIN、MAX等)转换为应用于整个 LINQ 查询的函数。 - 使用表别名作为范围变量。使用列别名作为匿名类型字段名称。
- 对多个列使用匿名类型 (
new {...})。 -
LEFT JOIN使用into进行模拟joinvariable 并从from执行另一个操作joinvariable 后跟.DefaultIfEmpty(). - 替换
COALESCE使用条件运算符 (?:) 和null测试。 - 翻译
IN至.Contains()和NOT IN至!...Contains(). - 翻译x
BETWEEN低AND最高到最低<=x&&x<=高。 -
SELECT *必须替换为 select range_variable 或对于连接，包含所有范围变量的匿名对象。 -
SELECT字段必须替换为select new {...}使用所有所需的字段或表达式创建一个匿名对象。 - 正确
FULL OUTER JOIN必须使用扩展方法来处理。
对于您的查询，您有 3 个基于 3 SELECT 的子查询s，您可以从内到外翻译它们:
var lowSerials = from Efn in _serialNumberContext.Efns
where Efn.Mid == mid
select Efn.LowSerial;
var serials = from Efn in _serialNumberContext.Efns
where Efn.Mid == mid &&
minSerial <= Efn.HighSerial + 1 && Efn.HighSerial + 1 <= maxSerial &&
!lowSerials.Contains(Efn.HighSerial + 1)
select Efn.HighSerial + 1;
var Target = serials.Min();
关于c# - 如何将复杂的 T-SQL 转换为 Linq，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/48895936/