如何将复杂的T-SQL转换为Linq

Question

我正在使用EntityFramework Core 2.0进行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，并且在处理T-SQL的这一特定段时遇到了困难；

        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此。

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生成了我在项目中拥有的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)
                            };

但是我无法弄清楚包装的T-SQL代码的Linq转换。

SET @Target = (SELECT MIN(A.[Serial]) 
                FROM ( 
                        ...
                        ...
                        ...) A)

如果有帮助，我将提供有关该项目的更多详细信息。

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);
    }

}

这是完整的旧版存储过程

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

要将SQL转换为LINQ查询理解：

1. 将子选择转换为单独声明的变量。
2. 以LINQ子句顺序转换每个子句，将单子运算符和集合运算符（ DISTINCT ， TOP ， MIN ， MAX等）转换为应用于整个LINQ查询的函数。
3. 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。
4. 对多个列使用匿名类型（ new { ... } ）。
5. LEFT JOIN通过使用模拟into joinvariable和从做另一个from所述joinvariable接着.DefaultIfEmpty()
6. 用条件运算符（ ?: COALESCE和null测试替换COALESCE 。
7. 翻译IN到.Contains()和NOT IN来! ... Contains()
8. 翻译X BETWEEN 低 AND 高到低 <= X && X <= 高 。
9. SELECT *必须替换为select range_variable，或者对于联接来说，是包含所有范围变量的匿名对象。
10. SELECT字段必须替换为select new { ... }创建具有所有所需字段或表达式的匿名对象。
11. 正确的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个SELECT的子查询，您可以从内而外转换它们：

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();