如何将复杂的T-SQL转换为Linq

Question

I am working in an Asp.NET Core 2.0 project, using EntityFramework Core 2.0.

I am trying to convert an existing legacy SQL stored procedures into Linq in EntityFramework Core and I am having difficulty with this particular segment of T-SQL;

        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)

I tried running it through Linqer v4.6 but it just basically passed the same from the SQL window into the Linq window.

I cut the Stored Procedure code down to this in Linqer;

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)

And Linqer produced Linq code that I have in my project as this;

                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)
                            };

But I can't figure out the Linq translation of the wrapping T-SQL code;

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

If it helps, I have provided some further details about the project;

The Efn SQL Server Efn table has the following fields;

    [Mid] INT NOT NULL,
    [Date] DATE NOT NULL,
    [LowSerial] BIGINT NOT NULL,
    [HighSerial] BIGINT NOT NULL

and in my project, I have an Efn entity class as follows;

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; }

}

Here is my dbcontext class

public class 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);
    }

}

Here is the complete legacy Stored Procedure

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

For translating SQL to LINQ query comprehension:

1. Translate subselects as separately declared variables.
2. Translate each clause in LINQ clause order, translating monadic and aggregate operators ( DISTINCT , TOP , MIN , MAX etc) into functions applied to the whole LINQ query.
3. Use table aliases as range variables. Use column aliases as anonymous type field names.
4. Use anonymous types ( new { ... } ) for multiple columns.
5. LEFT JOIN is simulated by using into joinvariable and doing another from from the joinvariable followed by .DefaultIfEmpty() .
6. Replace COALESCE with the conditional operator ( ?: )and a null test.
7. Translate IN to .Contains() and NOT IN to ! ... Contains() .
8. Translate x BETWEEN low AND high to low <= x && x <= high .
9. SELECT * must be replaced with select range_variable or for joins, an anonymous object containing all the range variables.
10. SELECT fields must be replaced with select new { ... } creating an anonymous object with all the desired fields or expressions.
11. Proper FULL OUTER JOIN must be handled with an extension method.

For your query, you have 3 sub-queries based on the 3 SELECT s and you can translate them from inside out:

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();