Fluent nHibernate，Hi-Lo 表，每行实体使用约定

Question

有没有办法通过约定来指定用于 Hi-Lo 值的表，每个实体都有一个每行条目（同时仍然让 nHibernate 为您创建表结构）？我想复制 Phil Haydon 写的关于 here 的博客，但不必手动管理表格。就目前而言，仅当您已经在表中为“TableKey”创建了适当的条目时，将他的每表行代码迁移到它自己的约定才有效。

或者，这可以通过 XML 映射实现吗？

如果所有其他方法都失败了，那么使用自定义生成器的唯一其他合适的选择是this post？

Answer 1

Fabio Maulo talked about this 在他的一篇按代码映射的帖子中。

通过代码示例映射：

mapper.BeforeMapClass += (mi, type, map) =>
    map.Id(idmap => idmap.Generator(Generators.HighLow,
        gmap => gmap.Params(new
        {
            table = "NextHighValues",
            column = "NextHigh",
            max_lo = 100,
            where = string.Format(
                "EntityName = '{0}'", type.Name.ToLowerInvariant())
        })));

对于 FluentNHibernate，您可以执行以下操作：

public class PrimaryKeyConvention : IIdConvention
{
    public void Apply(IIdentityInstance instance)
    {
        var type = instance.EntityType.Name;
        instance.Column(type + "Id");
        instance.GeneratedBy.HiLo(type, "NextHigh", "100", 
            x => x.AddParam("where", String.Format("EntityName = '{0}'", type));
    }
}

此外，Fabio 解释了如何使用 IAuxiliaryDatabaseObject 创建 Hi-Lo 脚本。

private static IAuxiliaryDatabaseObject CreateHighLowScript(
    IModelInspector inspector, IEnumerable<Type> entities)
{
    var script = new StringBuilder(3072);
    script.AppendLine("DELETE FROM NextHighValues;");
    script.AppendLine(
        "ALTER TABLE NextHighValues ADD EntityName VARCHAR(128) NOT NULL;");
    script.AppendLine(
        "CREATE NONCLUSTERED INDEX IdxNextHighValuesEntity ON NextHighValues " 
        + "(EntityName ASC);");
    script.AppendLine("GO");

    foreach (var entity in entities.Where(x => inspector.IsRootEntity(x)))
    {
        script.AppendLine(string.Format(
         "INSERT INTO [NextHighValues] (EntityName, NextHigh) VALUES ('{0}',1);",
         entity.Name.ToLowerInvariant()));
    }

    return new SimpleAuxiliaryDatabaseObject(
        script.ToString(), null, new HashedSet<string> {
           typeof(MsSql2005Dialect).FullName, typeof(MsSql2008Dialect).FullName 
        });
}

你会这样使用它：

configuration.AddAuxiliaryDatabaseObject(CreateHighLowScript(
    modelInspector, Assembly.GetExecutingAssembly().GetExportedTypes()));

Answer 2

对于 Fluent NHibernate 的用户，Anthony Dewhirst 在这里发布了一个不错的解决方案：http://www.anthonydewhirst.blogspot.co.uk/2012/02/fluent-nhibernate-solution-to-enable.html

Answer 3

在 Anthony Dewhirst 已经非常出色的解决方案的基础上，我得到了以下结果，其中增加了一些改进：

• 添加了接受标准，这样它就不会尝试处理非整数 Id 类型（例如 Guid），并且不会踩踏明确设置了生成器的 Id 映射
• 脚本生成考虑了方言

public class HiLoIdGeneratorConvention : IIdConvention, IIdConventionAcceptance
{
    public const string EntityColumnName = "entity";
    public const string MaxLo = "500";

    public void Accept(IAcceptanceCriteria<IIdentityInspector> criteria)
    {
        criteria
            .Expect(x => x.Type == typeof(int) || x.Type == typeof(uint) || x.Type == typeof(long) || x.Type == typeof(ulong)) // HiLo only works with integral types
            .Expect(x => x.Generator.EntityType == null); // Specific generator has not been mapped
    }

    public void Apply(IIdentityInstance instance)
    {
        instance.GeneratedBy.HiLo(TableGenerator.DefaultTableName, TableGenerator.DefaultColumnName, MaxLo,
                                  builder => builder.AddParam(TableGenerator.Where, string.Format("{0} = '{1}'", EntityColumnName, instance.EntityType.FullName)));
    }

    public static void CreateHighLowScript(NHibernate.Cfg.Configuration config)
    {
        var dialect = Activator.CreateInstance(Type.GetType(config.GetProperty(NHibernate.Cfg.Environment.Dialect))) as Dialect;
        var script = new StringBuilder();

        script.AppendFormat("DELETE FROM {0};", TableGenerator.DefaultTableName);
        script.AppendLine();
        script.AppendFormat("ALTER TABLE {0} {1} {2} {3} NOT NULL;", TableGenerator.DefaultTableName, dialect.AddColumnString, EntityColumnName, dialect.GetTypeName(SqlTypeFactory.GetAnsiString(128)));
        script.AppendLine();
        script.AppendFormat("CREATE NONCLUSTERED INDEX IX_{0}_{1} ON {0} ({1} ASC);", TableGenerator.DefaultTableName, EntityColumnName);
        script.AppendLine();
        if (dialect.SupportsSqlBatches)
        {
            script.AppendLine("GO");
            script.AppendLine();
        }
        foreach (var entityName in config.ClassMappings.Select(m => m.EntityName).Distinct())
        {
            script.AppendFormat("INSERT INTO [{0}] ({1}, {2}) VALUES ('{3}',1);", TableGenerator.DefaultTableName, EntityColumnName, TableGenerator.DefaultColumnName, entityName);
            script.AppendLine();
        }
        if (dialect.SupportsSqlBatches)
        {
            script.AppendLine("GO");
            script.AppendLine();
        }

        config.AddAuxiliaryDatabaseObject(new SimpleAuxiliaryDatabaseObject(script.ToString(), null));
    }
}