Fluent NHibernate mapping to a SQL Server CHAR(10) ID column

问题:

New to both NHibernate and Fluent NHibernate and I'm trying to resolve a performance problem in some inherited code caused by a conversion of a CHAR(10) column to NVARCHAR.

From SQL Profiler:

exec sp_executesql N'select mytestclas0_.LinkId as LinkId45_,     mytestclas0_.Href as Href45_,     mytestclas0_.LinkActive as LinkActive45_  from MessageLinks mytestclas0_  where mytestclas0_.LinkId=@p0',N'@p0 nvarchar(4000)',@p0=N'BzE2T48HMF' 

You can see the ID coming in from NHibernate is cast as a NVARCHAR.

Table definition:

CREATE TABLE [dbo].[MyTable](     [ID] [int] NULL,     [Href] [nvarchar](1000) NULL,     [LinkActive] [bit] NOT NULL,     [LinkId] [char](10) NOT NULL  ) 

The class file:

public class MyTestClass {     public MyTestClass() {}      public virtual string LinkId{ get; set; }     public virtual string Href{ get; set; }     public virtual bool LinkActive { get; set; } } 

The mapping file:

  public class MyTestClassMapping : ClassMap<MyTestClass> {     public MyTestClassMapping() {       Table("MyTable");        Id(x => x.LinkId).Length(10);       Map(x => x.LinkId);       Map(x => x.Href);       Map(x => x.LinkActive);     }   } 

I have tried a number of different things with the datatype of the LinkId and the mapping file, including these mappings:

    Id(x => x.LinkId).CustomSqlType("char(10)");     Id(x => x.LinkId).Length(10).CustomSqlType("char");     Id(x => x.LinkId).CustomSqlType("char"); 

I'm looking for a pointer to an example or documentation that explains how to get the ID passed in by NHibernate cast to a CHAR(10).

Thanks in advance for any help.

回答1:

The mapping should be like this (see the documentation 5.2.2. Basic value types):

Id(x => x.LinkId)         .CustomType("AnsiString")   ...   ; 

NHibernate type for char (non unicode string) is type="AnsiString" for xml mapping. the above is the way how to do that in fluent.

See similar story here: NHibernate Performance (Ansi String vs. Unicode String)

Side Note: I've never managed to specify length ... always it is generated by NHibernate varchar(8000), using MS SQL 2008 dialect...

回答2:

NHibernate MsSql2000Dialect and following versions define AnsiString correctly, also supporting length etc.

But, the current implementation of the SqlDriver got a change last year, see https://nhibernate.jira.com/browse/NH-3036 for details of the fix.

The code does now ignore the specified length and always uses the default. Default for AnsiString and some others is varchar(8000)

RegisterColumnType(DbType.AnsiString, SqlClientDriver.MaxSizeForLengthLimitedAnsiString, "VARCHAR($l)"); 

code from SqlDriver: setting default:

protected static void SetDefaultParameterSize(IDbDataParameter dbParam, SqlType sqlType) {     switch (dbParam.DbType)     {         case DbType.AnsiString:         case DbType.AnsiStringFixedLength:             dbParam.Size = MaxSizeForLengthLimitedAnsiString;             break; 

Bugfix:

    // Used from SqlServerCeDriver as well     public static void SetVariableLengthParameterSize(IDbDataParameter dbParam, SqlType sqlType)     {         SetDefaultParameterSize(dbParam, sqlType);          // no longer override the defaults using data from SqlType, since LIKE expressions needs larger columns         // https://nhibernate.jira.com/browse/NH-3036         //if (sqlType.LengthDefined && !IsText(dbParam, sqlType) && !IsBlob(dbParam, sqlType))         //{         //  dbParam.Size = sqlType.Length;         //}          if (sqlType.PrecisionDefined)         {             dbParam.Precision = sqlType.Precision;             dbParam.Scale = sqlType.Scale;         }     } 

This of cause means no matter what you specify, it will not matter at all for the parameters. One can argue if this change is a good thing or not, I guess it is not ;)

回答3:

This is a guess, as I've used CustomSqlType, but not personally with char.

  Id(x => x.LinkId).Length(10).CustomSqlType("char(10)"); 

or you may have to drop the Length.

  Id(x => x.LinkId).CustomSqlType("char(10)"); 

Here is a simiar:

Possible to use CustomSqlType with CompositeId?

文章来源: Fluent NHibernate mapping to a SQL Server CHAR(10) ID column