如何将复杂的 T-SQL 转换为 Linq

Question

我正在 Asp.NET Core 2.0 项目中工作，使用 EntityFramework Core 2.0。

我正在尝试将现有遗留 SQL 存储过程转换为 EntityFramework Core 中的 Linq，但我在处理 T-SQL;[=19 的这个特定部分时遇到困难=]

        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)

我通过 Linqer v4.6 尝试运行它，但它基本上只是将相同的内容从 SQL window 传递到 Linq window.

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；

                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更多详细信息；

Efn SQL 服务器 Efn table 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 class，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; }

}

这是我的数据库上下文 class

public class 序列号上下文：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);
    }

}

这是完整的遗留存储过程

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

Answer 1

用于将 SQL 转换为 LINQ 查询理解：

将 subselects 翻译成单独声明的变量。
翻译 LINQ 子句顺序中的每个子句，将单子和聚合运算符（DISTINCT、TOP、MIN、MAX 等）翻译成应用于整体的函数LINQ 查询。
使用 table 别名作为范围变量。使用列别名作为匿名类型字段名称。
对多列使用匿名类型 (new { ... })。
LEFT JOIN 是通过使用 into joinvariable 并从 from 中执行另一个 joinvariable[=69= 来模拟的] 然后是 .DefaultIfEmpty().

将 COALESCE 替换为条件运算符 (?:) 和 null 测试。

将 IN 翻译成 .Contains() 并将 NOT IN 翻译成 !...Contains().

将xBETWEENlowANDhigh翻译成低 <= x && x <= 高.

SELECT * 必须替换为 select range_variable 或对于联接，包含所有范围变量的匿名对象。

SELECT 字段必须替换为 select new { ... } 创建一个包含所有所需字段或表达式的匿名对象。

正确的FULL OUTER JOIN必须用扩展方法处理。

对于您的查询，您有 3 个 sub-queries 基于 3 个 SELECT，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();

如何将复杂的 T-SQL 转换为 Linq

How do I convert complex T-SQL into Linq

c#

tsql

linq

entity-framework-core

linqer