C# 实体框架如何管理到匿名类型的映射查询结果?
考虑下面的LINQ到实体查询示例C# 实体框架如何管理到匿名类型的映射查询结果?,c#,entity-framework,entity-framework-4,linq-to-entities,C#,Entity Framework,Entity Framework 4,Linq To Entities,考虑下面的LINQ到实体查询示例 from history in entities.foreignuserhistory select new { history.displayname, login=history.username, history.foreignuserid } ToTraceString()返回字符串如下所示: SELECT "Extent1"."foreignuserid" AS "foreignuserid", "Extent1"."displayname"
from history in entities.foreignuserhistory
select new { history.displayname, login=history.username, history.foreignuserid }
ToTraceString()
返回字符串如下所示:
SELECT "Extent1"."foreignuserid" AS "foreignuserid",
"Extent1"."displayname" AS "displayname",
"Extent1"."username" AS "username"
FROM "integration"."foreignuserhistory" AS "Extent1"
对我来说,问题是列的顺序与查询不同,并且在示例中不使用别名,如login
。实体框架在哪里存储匿名类型的映射信息
背景:我将使用LINQ to entity为批量操作开发带有选择操作的insert
更新:
除了未知的列到属性映射算法外,使用select插入并没有那么难。可以使用元数据获取目标
ObjectSet
的表名和列名,构建INSERT-INTO-tableName(column\u-name1,…)
sql语句字符串,然后附加一些ObjectQuery.ToTraceString
SELECT语句。然后使用((EntityConnection)ObjectContext.Connection.StoreConnection)创建带有结果文本的DbCommand
,并从ObjectQuery
中填充命令参数。因此,问题是要在插入的记录和选定的记录中找到匹配的列顺序。在查询中列的别名如何不重要,它们的顺序也不重要。实体框架处理用每个结果填充匿名类型的新实例,这就是获得别名的地方,如login
作为旁注,我认为实体框架可能并不像您所想的那样工作。不能像使用普通SQL查询那样在单个操作中执行选择/插入操作。实体框架将执行您的选择,返回结果,使用这些结果创建实体的新实例(或者在您的情况下是匿名类型),然后您必须使用每个结果创建目标类型的新实例,并将每个实例添加到实体/对象上下文中,最后,在实体/对象上下文上调用SaveChanges。这将导致为您添加的每个新实体执行单个insert语句
如果希望在单个操作中完成所有操作,而不为每个记录实例化新实体,则需要使用在上下文中映射的存储过程,或者使用
更新:根据您的回答,您真正了解的是元编程,它更依赖于您的实体模型,而不是实际使用实体框架。我不知道您使用的是什么版本的EF(EF 4.0?4.1 w/code first和DbContext?),但我在EF 4.0中使用C#POCO模板取得了很多成功(POCO模板是从在线visual studio库下载的)。它使用T4模板从.edmx数据模型生成POCO类。在T4模板中,您可以向上下文中添加基本上调用ExecuteStoreCommand
的方法,但不同之处在于您可以生成基于数据模型执行的查询。这样,每当数据模型发生更改时,您的查询都会与更改保持同步。以下是我的解决方案,涉及隐私和内部内容。它与反射一起移动到缓存查询计划中,缓存查询计划将在调用或执行查询后存在,以获得所谓的\u columnMap
。列映射包含按匿名对象属性顺序排列的ScalarColumnMap
对象,并使用ColumnPos
属性指向相应的列位置
using System;
using System.Data.Objects;
using System.Reflection;
static class EFQueryUtils
{
public static int[] GetPropertyPositions(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[]");
int n = columnMapProperties.Length;
int[] propertyPositions = new int[n];
for (int 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");
}
}
使用系统;
使用System.Data.Object;
运用系统反思;
静态类EFQueryUtils
{
公共静态int[]GetPropertyPositions(ObjectQuery)
{
//获取私有ObjectQueryState ObjectQuery.\u状态;
//内部类的实际类型
//System.Data.Objects.Elink.ElinkQueryState
对象queryState=GetProperty(查询,“queryState”);
AssertNonNullAndOfType(queryState,“System.Data.Objects.elink.elinkQueryState”);
//获取受保护的ObjectQueryExecutionPlan ObjectQueryState.\u cachedPlan;
//实际类型内部密封类
//System.Data.Objects.Internal.ObjectQueryExecutionPlan
对象计划=GetField(queryState,“\u cachedPlan”);
AssertNonNullAndOfType(计划,“System.Data.Objects.Internal.ObjectQueryExecutionPlan”);
//获取内部只读DbCommandDefinition对象QueryExecutionPlan.CommandDefinition;
//实际类型内部密封类
//System.Data.EntityClient.EntityCommandDefinition
对象commandDefinition=GetField(计划,“commandDefinition”);
AssertNonNullAndOfType(commandDefinition,“System.Data.EntityClient.EntityCommandDefinition”);
//获取专用只读IColumnMapGenerator EntityCommandDefinition.\u columnMapGenerator;
//实际类型的私有密封类
//System.Data.EntityClient.EntityCommandDefinition.ConstantColumnMapGenerator
对象columnMapGenerator=GetField(commandDefinition,“\u columnMapGenerator”);
AssertNonNullAndOfType(columnMapGenerator,“System.Data.EntityClient.EntityCommandDefinition+ConstantColumnMapGenerator”);
//获取私有只读ColumnMap ConstantColumnMapGenerator.\u ColumnMap;
//内部类的实际类型
//System.Data.Query.InternalTrees.SimpleCollectionColumnMap
对象columnMap=GetField(columnMapGenerator,“\u columnMap”);
AssertNonNullAndOfType(columnMap,“System.Data.Query.InternalTrees.SimpleCollectionColumnMap”);
//获取内部ColumnMap CollectionColumnMap.Element;
//内部类的实际类型
//System.Data.Query.InternalTrees.RecordColumnMap
对象columnMapElement=GetProperty(columnMap,“元素”);
AssertNonNullAndOfType(columnMapElement,“System.Data.Query.InternalTrees.RecordColumnMap”);
//获取内部ColumnMap[]StructuredColumnMap.Properties;
int Insert<T>(IQueryable query,IQueryable<T> targetSet)
{
var oQuery=(ObjectQuery)this.QueryProvider.CreateQuery(query.Expression);
var sql=oQuery.ToTraceString();
var propertyPositions = GetPropertyPositions(oQuery);
var targetSql=((ObjectQuery)targetSet).ToTraceString();
var queryParams=oQuery.Parameters.ToArray();
System.Diagnostics.Debug.Assert(targetSql.StartsWith("SELECT"));
var queryProperties=query.ElementType.GetProperties();
var selectParams=sql.Substring(0,sql.IndexOf("FROM "));
var selectAliases=Regex.Matches(selectParams,@"\sAS \[([a-zA-Z0-9_]+)\]").Cast<Match>().Select(m=>m.Groups[1].Value).ToArray();
var from=targetSql.Substring(targetSql.LastIndexOf("FROM [")+("FROM [".Length-1));
var fromAlias=from.Substring(from.LastIndexOf("AS ")+"AS ".Length);
var target=targetSql.Substring(0,targetSql.LastIndexOf("FROM ["));
target=target.Replace("SELECT","INSERT INTO "+from+" (")+")";
target=target.Replace(fromAlias+".",string.Empty);
target=Regex.Replace(target,@"\sAS \[[a-zA-z0-9]+\]",string.Empty);
var insertParams=target.Substring(target.IndexOf('('));
target = target.Substring(0, target.IndexOf('('));
var names=Regex.Matches(insertParams,@"\[([a-zA-Z0-9]+)\]");
var remaining=names.Cast<Match>().Select(m=>m.Groups[1].Value).Where(m=>queryProperties.Select(qp=>qp.Name).Contains(m)).ToArray(); //scrape out items that the anonymous select doesn't include a name/value for
//selectAliases[propertyPositions[10]]
//remaining[10]
var insertParamsOrdered = remaining.Select((s, i) => new { Position = propertyPositions[i], s })
.OrderBy(o => o.Position).Select(x => x.s).ToArray();
var insertParamsDelimited = insertParamsOrdered.Aggregate((s1, s2) => s1 + "," + s2);
var commandText = target + "(" + insertParamsDelimited + ")" + sql;
var result=this.ExecuteStoreCommand(commandText,queryParams.Select(qp=>new System.Data.SqlClient.SqlParameter{ ParameterName=qp.Name, Value=qp.Value}).ToArray());
return result;
}