我正在尝试将IQueryable对象转换为DataTable.这是我想要转换为DataTable的查询示例：
var query = DbContext.someObjectSet.Select(x => new { PropertyName1 = x.ColumnName1,PropertyName2 = x.ColumnName2 });
new { PropertyName1 = x.ColumnName1,PropertyName2 = x.ColumnName2 }
谷歌搜索此问题后,我遇到了以下代码,将IQueryable对象转换为DataTable：
public static DataTable EntityToDatatable(this IQueryable result)
{
ObjectQuery query = (result as ObjectQuery);
ObjectContext context = query.Context;
EntityConnection entityCon = (context.Connection as EntityConnection);
using (sqlConnection sqlCon = new sqlConnection(entityCon.StoreConnection.ConnectionString))
{
using (sqlCommand cmd = new sqlCommand(query.ToTraceString(),sqlCon))
{
foreach (var param in query.Parameters)
{
cmd.Parameters.AddWithValue(param.Name,param.Value);
}
using (sqlDataAdapter dataAdapter = new sqlDataAdapter(cmd))
{
using (DataTable dataTable = new DataTable())
{
dataAdapter.Fill(dataTable);
return dataTable;
}
}
}
}
}
上面的代码“工作”,ToTraceString()方法的sql语句如下：
SELECT [Extent1].[ColumnName1] AS [ColumnName1],[Extent1].[ColumnName2] AS [ColumnName2] FROM [dbo].[TableName] AS [Extent1]
问题：sql语句的列名(即columnName1和columnName2)与对象的属性名称(即PropertyName1和PropertyName2)不对应,如果调用了ToList()或AsEnumerable()方法,这些属性将被实现查询.如果sql语句列与匿名对象属性的顺序相同,那就不会那么糟糕了……但是,情况并非总是这样.在某处(我猜在IQueryable对象内)必须在sql语句列名和生成的匿名对象属性名之间进行映射.
有谁知道如何获得这个映射？
解决方法
我设法找到了解决问题的方法：
首先,您需要以下代码(从How does Entity Framework manage mapping query result to anonymous type?开始),它将我的匿名对象属性的位置映射到sql语句列位置：
public static Int32[] GetPropertyPositions(this ObjectQuery query)
{
// get private ObjectQueryState ObjectQuery._state;
// of actual type internal class
// System.Data.Objects.ELinq.ELinqQueryState
Object queryState = GetProperty(query,"QueryState");
AssertNonNullAndOfType(queryState,"System.Data.Objects.ELinq.ELinqQueryState");
// get protected ObjectQueryExecutionPlan ObjectQueryState._cachedplan;
// of actual type internal sealed class
// System.Data.Objects.Internal.ObjectQueryExecutionPlan
Object plan = GetField(queryState,"_cachedplan");
AssertNonNullAndOfType(plan,"System.Data.Objects.Internal.ObjectQueryExecutionPlan");
// get internal readonly DbCommandDeFinition ObjectQueryExecutionPlan.CommandDeFinition;
// of actual type internal sealed class
// System.Data.EntityClient.EntityCommandDeFinition
Object commandDeFinition = GetField(plan,"CommandDeFinition");
AssertNonNullAndOfType(commandDeFinition,"System.Data.EntityClient.EntityCommandDeFinition");
// get private readonly IColumnMapGenerator EntityCommandDeFinition._columnMapGenerator;
// of actual type private sealed class
// System.Data.EntityClient.EntityCommandDeFinition.ConstantColumnMapGenerator
Object columnMapGenerator = GetField(commandDeFinition,"_columnMapGenerator");
AssertNonNullAndOfType(columnMapGenerator,"System.Data.EntityClient.EntityCommandDeFinition+ConstantColumnMapGenerator");
// get private readonly ColumnMap ConstantColumnMapGenerator._columnMap;
// of actual type internal class
// System.Data.Query.InternalTrees.SimpleCollectionColumnMap
Object columnMap = GetField(columnMapGenerator,"_columnMap");
AssertNonNullAndOfType(columnMap,"System.Data.Query.InternalTrees.SimpleCollectionColumnMap");
// get internal ColumnMap CollectionColumnMap.Element;
// of actual type internal class
// System.Data.Query.InternalTrees.RecordColumnMap
Object columnMapElement = GetProperty(columnMap,"Element");
AssertNonNullAndOfType(columnMapElement,"System.Data.Query.InternalTrees.RecordColumnMap");
// get internal ColumnMap[] StructuredColumnMap.Properties;
// array of internal abstract class
// System.Data.Query.InternalTrees.ColumnMap
Array columnMapProperties = GetProperty(columnMapElement,"Properties") as Array;
AssertNonNullAndOfType(columnMapProperties,"System.Data.Query.InternalTrees.ColumnMap[]");
Int32 n = columnMapProperties.Length;
Int32[] propertyPositions = new Int32[n];
for (Int32 i = 0; i < n; ++i)
{
// get value at index i in array
// of actual type internal class
// System.Data.Query.InternalTrees.ScalarColumnMap
Object column = columnMapProperties.GetValue(i);
AssertNonNullAndOfType(column,"System.Data.Query.InternalTrees.ScalarColumnMap");
//string colName = (string)GetProp(column,"Name");
// can be used for more advanced bingings
// get internal int ScalarColumnMap.ColumnPos;
Object columnPositionOfAProperty = GetProperty(column,"ColumnPos");
AssertNonNullAndOfType(columnPositionOfAProperty,"system.int32");
propertyPositions[i] = (int)columnPositionOfAProperty;
}
return propertyPositions;
}
static object GetProperty(object obj,string propName)
{
PropertyInfo prop = obj.GetType().GetProperty(propName,BindingFlags.NonPublic | BindingFlags.Instance);
if (prop == null) throw EFChangedException();
return prop.GetValue(obj,new object[0]);
}
static object GetField(object obj,string fieldName)
{
FieldInfo field = obj.GetType().GetField(fieldName,BindingFlags.NonPublic | BindingFlags.Instance);
if (field == null) throw EFChangedException();
return field.GetValue(obj);
}
static void AssertNonNullAndOfType(object obj,string fullName)
{
if (obj == null) throw EFChangedException();
string typeFullName = obj.GetType().FullName;
if (typeFullName != fullName) throw EFChangedException();
}
static InvalidOperationException EFChangedException()
{
return new InvalidOperationException("Entity Framework internals has changed,please review and fix reflection code");
}
然后我可以修改EntityToDatatable方法,如下所示：
public static DataTable EntityToDatatable(this IQueryable query)
{
sqlConnection sqlConnection = null;
sqlCommand sqlCommand = null;
sqlDataAdapter sqlDataAdapter = null;
DataTable dataTable = null;
try
{
ObjectQuery objectQuery = (query as ObjectQuery);
ObjectContext objectContext = objectQuery.Context;
EntityConnection entityConnection = (objectContext.Connection as EntityConnection);
sqlConnection = new sqlConnection(entityConnection.StoreConnection.ConnectionString);
sqlCommand = new sqlCommand(objectQuery.ToTraceString(),sqlConnection);
foreach (var parameter in objectQuery.Parameters)
{
sqlCommand.Parameters.AddWithValue(parameter.Name,parameter.Value);
}
sqlDataAdapter = new sqlDataAdapter(sqlCommand);
dataTable = new DataTable();
sqlDataAdapter.Fill(dataTable);
// Get the mapping between the object property position and
// the sql statment column position.
Int32[] propertyPositions = objectQuery.GetPropertyPositions();
// Create a column name to column position (ordinal) lookup.
Dictionary<String,Int32> mapColumnNametoColumnPosition = new Dictionary<string,int>();
// Populate the lookup.
for (Int32 i = 0; i < propertyPositions.Length; ++i)
{
mapColumnNametoColumnPosition.Add(dataTable.Columns[propertyPositions[i]].ColumnName,i);
}
// Get the object's property @R_584_4045@ion.
PropertyInfo[] pi = query.GetType().GetGenericArguments()[0].GetProperties();
// Iterate through the lookup and change the position of the datatable columns.
// The order of the datatable columns will Now correspond to the order of the object
// properties.
foreach (var map in mapColumnNametoColumnPosition)
{
// Change the column position.
dataTable.Columns[map.Key].Setordinal(map.Value);
// Change the column name.
dataTable.Columns[map.Key].ColumnName = pi[map.Value].Name;
}
return dataTable;
}
catch (Exception ex)
{
// Something went wrong and we're going to raise an exception...we
// might as well dispose of the datatable if it exists because it's
// not going to be used.
if (dataTable != null) dataTable.dispose();
throw new Exception("IQueryable to DataTable conversion error.",ex);
}
finally
{
// Do some cleanup on objects that are no longer needed.
if (sqlDataAdapter != null) sqlDataAdapter.dispose();
if (sqlCommand != null) sqlCommand.dispose();
if (sqlConnection != null) sqlConnection.dispose();
}
}
版权声明：本文内容由互联网用户自发贡献，该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容， 请发送邮件至 [email protected] 举报，一经查实，本站将立刻删除。
