实现IBatisNet的Dialect分页
Hibernate有其独有的Dialect，对不同的数据库实现sql的分页。
用过MyBatis for Java，它可以拦截SQL语句，通过Interceptor对原始的sql语句进行修改，也就是可以实现自定义Dialect，实现与Hibernate相同效果的分页Dialect。
可是最近搞了个IBatisNet+Spring.Net的框架，IBatisNet是ibatis for Java版本转移过来的。
它没有MyBatis新版本所增加的功能，而IBatisNet自带的分页是通过IDataReader实现的逻辑分页，虽说在局域网环境上，对内存和带宽的影响不是很大，但个人习惯上还是看着很恶心。
上网找了很多天的资料，并没有发现有相当的资料，也似乎没有人这样做过（或许是做了没有共享出来）。
但无意中发现有代码是可以获取到运行时的sql语句的，于是把IBatisNet源码中的实现重新搬出来，修改了一下，算是也能实现Dialect的效果。
主要代码如下：
public static IList QueryPageList(ISqlMapper sqlMap, String statementName, Object parameter, int offset, int limit) { IMappedStatement statement = sqlMap.GetMappedStatement(statementName); if(!sqlMap.IsSessionStarted) { sqlMap.OpenConnection(); } RequestScope request = statement.Statement.Sql.GetRequestScope(statement, parameter, sqlMap.LocalSession); request.PreparedStatement.PreparedSql = dialect.GetLimitString(request.PreparedStatement.PreparedSql, offset, limit); statement.PreparedCommand.Create(request, sqlMap.LocalSession, statement.Statement, parameter); return RunQueryForList(request, sqlMap.LocalSession, parameter, statement.Statement); } public static IList<T> QueryPageList<T>(ISqlMapper sqlMap, String statementName, Object parameter, int offset, int limit) { IMappedStatement statement = sqlMap.GetMappedStatement(statementName); if(!sqlMap.IsSessionStarted) { sqlMap.OpenConnection(); } RequestScope request = statement.Statement.Sql.GetRequestScope(statement, new Hashtable(), sqlMap.LocalSession); request.PreparedStatement.PreparedSql = dialect.GetLimitString(request.PreparedStatement.PreparedSql, offset, limit); statement.PreparedCommand.Create(request, sqlMap.LocalSession, statement.Statement, parameter); return (List<T>)RunQueryForList<T>(request, sqlMap.LocalSession, parameter, statement.Statement); } private static IList RunQueryForList(RequestScope request, ISqlMapSession session, object parameterObject, IStatement _statement) { IList list = null; using(IDbCommand command = request.IDbCommand) { list = (_statement.ListClass == null)? (new ArrayList()):(_statement.CreateInstanceOfListClass()); IDataReader reader = command.ExecuteReader(); try { while(reader.Read()) { object obj = ResultStrategyFactory.Get(_statement).Process(request, ref reader, null); if(obj != BaseStrategy.SKIP) { list.Add(obj); } } } catch { throw; } finally { reader.Close(); reader.Dispose(); } ExecutePostSelect(request); RetrieveOutputParameters(request, session, command, parameterObject); } return list; } private static IList<T> RunQueryForList<T>(RequestScope request, ISqlMapSession session, object parameterObject, IStatement _statement) { IList<T> list = new List<T>(); using(IDbCommand command = request.IDbCommand) { list = (_statement.ListClass == null) ? (new List<T>()) : (_statement.CreateInstanceOfGenericListClass<T>()); IDataReader reader = command.ExecuteReader(); try { while(reader.Read()) { object obj = ResultStrategyFactory.Get(_statement).Process(request, ref reader, null); if(obj != BaseStrategy.SKIP) { list.Add((T)obj); } } } catch { throw; } finally { reader.Close(); reader.Dispose(); } ExecutePostSelect(request); RetrieveOutputParameters(request, session, command, parameterObject); } return list; } private static void ExecutePostSelect(RequestScope request) { while(request.QueueSelect.Count > 0) { PostBindind postSelect = request.QueueSelect.Dequeue() as PostBindind; PostSelectStrategyFactory.Get(postSelect.Method).Execute(postSelect, request); } } private static void RetrieveOutputParameters(RequestScope request, ISqlMapSession session, IDbCommand command, object result) { if(request.ParameterMap != null) { int count = request.ParameterMap.PropertiesList.Count; for(int i = 0; i < count; i++) { IBatisNet.DataMapper.Configuration.ParameterMapping.ParameterProperty mapping = request.ParameterMap.GetProperty(i); if(mapping.Direction == ParameterDirection.Output || mapping.Direction == ParameterDirection.InputOutput) { string parameterName = string.Empty; if(session.DataSource.DbProvider.UseParameterPrefixInParameter == false) { parameterName = mapping.ColumnName; } else { parameterName = session.DataSource.DbProvider.ParameterPrefix + mapping.ColumnName; } if(mapping.TypeHandler == null) // Find the TypeHandler { lock(mapping) { if(mapping.TypeHandler == null) { Type propertyType = ObjectProbe.GetMemberTypeForGetter(result, mapping.PropertyName); mapping.TypeHandler = request.DataExchangeFactory.TypeHandlerFactory.GetTypeHandler(propertyType); } } } // Fix IBATISNET-239 //"Normalize" System.DBNull parameters IDataParameter dataParameter = (IDataParameter)command.Parameters[parameterName]; object dbValue = dataParameter.Value; object value = null; bool wasNull = (dbValue == DBNull.Value); if(wasNull) { if(mapping.HasNullValue) { value = mapping.TypeHandler.ValueOf(mapping.GetAccessor.MemberType, mapping.NullValue); } else { value = mapping.TypeHandler.NullValue; } } else { value = mapping.TypeHandler.GetDataBaseValue(dataParameter.Value, result.GetType()); } request.IsRowDataFound = request.IsRowDataFound || (value != null); request.ParameterMap.SetOutputParameter(ref result, mapping, value); } } } }
其中的dialect.GetLimitString()，你们可以用接口的方式，定义针对不同数据库的分页sql，拼接为分页sql即可。
而ExecutePostSelect和RetrieveOutputParameters方法，则是从按源实现代码来调用的，因为无法调用其原始代码，所以自己重新实现了一部分。