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

Question

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'

您可以看到来自NHibernate的ID被转换为NVARCHAR.

表定义:

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

类文件:

public class MyTestClass {
    public MyTestClass() {}

    public virtual string LinkId{ get; set; }
    public virtual string Href{ get; set; }
    public virtual bool LinkActive { get; set; }
}

映射文件:

  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);
    }
  }

我用LinkId的数据类型和映射文件尝试了许多不同的东西,包括这些映射:

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

我正在寻找一个指向示例或文档的指针,该指针解释了如何将NHibernate传入的ID传入一个CHAR(10).

在此先感谢您的帮助.

Answer 1

映射应该是这样的(参见文档5.2.2.基本值类型):

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

char(非unicode字符串)的NHibernate类型用于type="AnsiString"xml映射.以上是如何以流利的方式做到这一点的方式.

在这里看到类似的故事:NHibernate性能(Ansi字符串与Unicode字符串)

旁注:我从未设法指定长度...总是由NHibernate varchar(8000)生成,使用MS SQL 2008方言...

Answer 2

NHibernate MsSql2000Dialect和以下版本正确定义了AnsiString，还支持长度等。

但是，SqlDriver的当前实现在去年进行了更改，有关修复程序的详细信息，请参见https://nhibernate.jira.com/browse/NH-3036。

该代码现在忽略指定的长度，并始终使用默认值。AnsiString和其他一些的默认值为varchar（8000）

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

SqlDriver中的代码：设置默认值：

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

错误修正：

    // 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;
        }
    }

原因是指，无论您指定什么内容，对于参数而言都没有关系。有人可以争辩说这种改变是否是一件好事，我想那不是;）