使用Oracle的NHibernate多查询/期货

Question

我试图在NHibernate 3.2和Oracle 11gR2中使用期货.虽然我不确定,但这似乎并不支持.我在NHibernate Jira上发现了这个问题,这使得它看起来像Oracle的未来可能.有谁知道如何让期货与Oracle合作？Oracle不受支持的原因究竟是什么？

更新

根据这里的评论,我尝试使用HQL multiquery.我在执行时遇到异常_nhSession.CreateMultiQuery();这是例外:

The driver NHibernate.Driver.OracleDataClientDriver does not support multiple queries.

我还能尝试什么？我使用了错误的驱动程序吗？

Answer 1

我想分享一下NHibernate Future查询如何与Oracle协同工作的方式.您可以将以下两个类EnhancedOracleDataClientDriver和EnhancedOracleResultSetsCommand添加到您的项目中,并将NHibernate配置为使用EnhancedOracleDataClientDriver类作为数据库驱动程序.我很感激这种方法是否适用于其他人的反馈.这是上述类的源代码.

EnhancedOracleDataClientDriver.cs

using NHibernate.Engine;

namespace NHibernate.Driver
{
    public class EnhancedOracleDataClientDriver : OracleDataClientDriver
    {
        public override bool SupportsMultipleQueries
        {
            get
            {
                return true;
            }
        }

        public override IResultSetsCommand GetResultSetsCommand(ISessionImplementor session)
        {
            return new EnhancedOracleResultSetsCommand(session);
        }
    }
}

EnhancedOracleResultSetsCommand.cs

using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Reflection;
using NHibernate.Engine;
using NHibernate.SqlCommand;
using NHibernate.SqlTypes;
using NHibernate.Util;

namespace NHibernate.Driver
{
    public class EnhancedOracleResultSetsCommand : BasicResultSetsCommand
    {
        private const string driverAssemblyName = "Oracle.DataAccess";

        private SqlString sqlString = new SqlString();
        private int cursorCount = 0;
        private readonly PropertyInfo oracleDbType;
        private readonly object oracleDbTypeRefCursor;

        public EnhancedOracleResultSetsCommand(ISessionImplementor session)
            : base(session)
        {
            System.Type parameterType = ReflectHelper.TypeFromAssembly("Oracle.DataAccess.Client.OracleParameter", driverAssemblyName, false);
            oracleDbType = parameterType.GetProperty("OracleDbType");

            System.Type oracleDbTypeEnum = ReflectHelper.TypeFromAssembly("Oracle.DataAccess.Client.OracleDbType", driverAssemblyName, false);
            oracleDbTypeRefCursor = System.Enum.Parse(oracleDbTypeEnum, "RefCursor");
        }

        public override void Append(ISqlCommand command)
        {
            Commands.Add(command);
            sqlString = sqlString.Append("\nOPEN :cursor")
                .Append(Convert.ToString(cursorCount++))
                .Append("\nFOR\n")
                .Append(command.Query).Append("\n;\n");
        }

        public override SqlString Sql
        {
            get { return sqlString; }
        }

        public override IDataReader GetReader(int? commandTimeout)
        {
            var batcher = Session.Batcher;
            SqlType[] sqlTypes = Commands.SelectMany(c => c.ParameterTypes).ToArray();
            ForEachSqlCommand((sqlLoaderCommand, offset) => sqlLoaderCommand.ResetParametersIndexesForTheCommand(offset));

            sqlString = sqlString.Insert(0, "\nBEGIN\n").Append("\nEND;\n");

            var command = batcher.PrepareQueryCommand(CommandType.Text, sqlString, sqlTypes);
            if (commandTimeout.HasValue) {
                command.CommandTimeout = commandTimeout.Value;
            }

            BindParameters(command);

            for (int cursorIndex = 0; cursorIndex < cursorCount; cursorIndex++) {
                IDbDataParameter outCursor = command.CreateParameter();
                oracleDbType.SetValue(outCursor, oracleDbTypeRefCursor, null);
                outCursor.ParameterName = ":cursor" + Convert.ToString(cursorIndex);
                outCursor.Direction = ParameterDirection.Output;
                command.Parameters.Add(outCursor);
            }

            return new BatcherDataReaderWrapper(batcher, command);
        }
    }
}

Answer 2

三年前,我发布了"NHibernate多查询/期货与Oracle"问题的答案,以及如何使未来的查询与Oracle协同工作的解决方案.就像将两个派生类EnhancedOracleDataClientDriver和EnhancedOracleResultSetsCommand添加到项目中,并将NHibernate配置为使用EnhancedOracleDataClientDriver类作为数据库驱动程序一样简单.

我最近检查了这个问题https://nhibernate.jira.com/browse/NH-2170,并发现开箱即用的NHibernate仍然不支持Oracle的期货.另外,如果我可以分享有关推导这种"增强型"实施方法的任何来源和/或方法,我在StackOverflow上得到了Ruben的问题.此外,有些人测试了这种"增强"方法,并对SQL Server未来没有注意到性能提升这一事实感到失望.

所以我决定花一些时间重新审视这个问题,试图分析和优化"增强"方法.

以下是我对探查器的调查结果:

1. 在Oracle.ManagedDataAccess提供程序中,按名称执行参数绑定比位置参数绑定慢.我测试了一个包含总共500个命名参数的多标准,并且分析器向我展示了在执行命令之前,Oracle提供程序花费了将近1秒来将命名参数转换为位置参数.我相信即使是具有500个命名参数的常规(非未来)查询也会遇到类似的性能损失.因此,一个瓶颈是"command.BindByName = true;".
2. 将多个查询组合到一个批处理中时,应使用SqlStringBuilder.Add(...)(而不是SqlString.Append(...)).这与组合字符串相同:StringBuilder的执行方式优于String.

因此,在仔细分析构建SQL命令并将其组合成批处理的NHibernate源代码之后,我推出了"增强"方法的第2版.我希望NHibernate核心团队会注意到这一点,并考虑将Oracle的期货添加到我最喜欢的ORM中.

顺便说一句,"增强"方法依赖于Oracle refcursors(批处理中每个查询的一个输出refcursor),并且每个会话都有Oracle限制的最大游标,我们必须注意(Oracle XE上的默认值最多为300个游标) ).

用法.将以下两个类EnhancedOracleManagedDataClientDriver和EnhancedOracleManagedResultSetsCommand添加到项目中,并配置NHibernate以使用EnhancedOracleManagedDataClientDriver类作为数据库驱动程序.

EnhancedOracleManagedDataClientDriver.cs

using System;
using System.Data;
using System.Reflection;
using NHibernate.Engine;
using NHibernate.SqlTypes;
using NHibernate.Util;

namespace NHibernate.Driver
{
    public class EnhancedOracleManagedDataClientDriver : OracleManagedDataClientDriver
    {
        private readonly PropertyInfo _oracleCommandBindByName;
        private readonly PropertyInfo _oracleDbType;
        private readonly object _oracleDbTypeRefCursor;

        public EnhancedOracleManagedDataClientDriver()
        {
            _oracleCommandBindByName = ReflectHelper.TypeFromAssembly(
                "Oracle.ManagedDataAccess.Client.OracleCommand", "Oracle.ManagedDataAccess", true).GetProperty("BindByName");
            _oracleDbType = ReflectHelper.TypeFromAssembly(
                "Oracle.ManagedDataAccess.Client.OracleParameter", "Oracle.ManagedDataAccess", true).GetProperty("OracleDbType");
            var enumType = ReflectHelper.TypeFromAssembly(
                "Oracle.ManagedDataAccess.Client.OracleDbType", "Oracle.ManagedDataAccess", true);
            _oracleDbTypeRefCursor = Enum.Parse(enumType, "RefCursor");
        }

        public override bool SupportsMultipleQueries => true;

        public override IResultSetsCommand GetResultSetsCommand(ISessionImplementor session)
        {
            return new EnhancedOracleManagedResultSetsCommand(session);
        }

        protected override void InitializeParameter(IDbDataParameter dbParam, string name, SqlType sqlType)
        {
            // this "exotic" parameter type will actually mean output refcursor
            if (sqlType.DbType == DbType.VarNumeric)
            {
                dbParam.ParameterName = FormatNameForParameter(name);
                dbParam.Direction = ParameterDirection.Output;
                _oracleDbType.SetValue(dbParam, _oracleDbTypeRefCursor, null);
            }
            else
                base.InitializeParameter(dbParam, name, sqlType);
        }

        protected override void OnBeforePrepare(IDbCommand command)
        {
            base.OnBeforePrepare(command);

            if (command.CommandText.StartsWith("\nBEGIN -- multi query\n"))
            {
                // for better performance, in multi-queries, 
                // we switch to parameter binding by position (not by name)
                this._oracleCommandBindByName.SetValue(command, false, null);
                command.CommandText = command.CommandText.Replace(":p", ":");
            }
        }
    }
}

EnhancedOracleManagedResultSetsCommand.cs

using System.Data;
using System.Linq;
using NHibernate.Engine;
using NHibernate.Impl;
using NHibernate.Loader.Custom;
using NHibernate.Loader.Custom.Sql;
using NHibernate.SqlCommand;
using NHibernate.SqlTypes;
using NHibernate.Type;

namespace NHibernate.Driver
{
    public class EnhancedOracleManagedResultSetsCommand : BasicResultSetsCommand
    {
        private readonly SqlStringBuilder _sqlStringBuilder = new SqlStringBuilder();
        private SqlString _sqlString = new SqlString();
        private QueryParameters _prefixQueryParameters;
        private CustomLoader _prefixLoader;

        public EnhancedOracleManagedResultSetsCommand(ISessionImplementor session)
            : base(session) {}

        public override SqlString Sql => _sqlString;

        public override void Append(ISqlCommand command)
        {
            if (_prefixLoader == null)
            {
                var prefixQuery = (SqlQueryImpl)((ISession)Session)
                    // this SQL query fragment will prepend every SELECT query in multiquery/multicriteria 
                    .CreateSQLQuery("\nOPEN :crsr \nFOR\n")
                    // this "exotic" parameter type will actually mean output refcursor
                    .SetParameter("crsr", 0, new DecimalType(new SqlType(DbType.VarNumeric)));

                _prefixQueryParameters = prefixQuery.GetQueryParameters();

                var querySpecification = prefixQuery.GenerateQuerySpecification(_prefixQueryParameters.NamedParameters);

                _prefixLoader = new CustomLoader(new SQLCustomQuery(querySpecification.SqlQueryReturns, querySpecification.QueryString,
                    querySpecification.QuerySpaces, Session.Factory), Session.Factory);
            }

            var prefixCommand = _prefixLoader.CreateSqlCommand(_prefixQueryParameters, Session);

            Commands.Add(prefixCommand);
            Commands.Add(command);

            _sqlStringBuilder.Add(prefixCommand.Query);
            _sqlStringBuilder.Add(command.Query).Add("\n;\n\n");
        }

        public override IDataReader GetReader(int? commandTimeout)
        {
            var batcher = Session.Batcher;
            var sqlTypes = Commands.SelectMany(c => c.ParameterTypes).ToArray();
            ForEachSqlCommand((sqlLoaderCommand, offset) => sqlLoaderCommand.ResetParametersIndexesForTheCommand(offset));

            _sqlStringBuilder.Insert(0, "\nBEGIN -- multi query\n").Add("\nEND;\n");
            _sqlString = _sqlStringBuilder.ToSqlString();

            var command = batcher.PrepareQueryCommand(CommandType.Text, _sqlString, sqlTypes);
            if (commandTimeout.HasValue)
                command.CommandTimeout = commandTimeout.Value;

            BindParameters(command);
            return new BatcherDataReaderWrapper(batcher, command);
        }
    }
}