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 });
请注意在Select方法中创建的匿名对象以及属性的名称：
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？
最佳答案 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 information.
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();
}
}
