[英]Entity Framework 4.1: Unable to cast from DbQuery to ObjectQuery
I have the following code: 我有以下代码:
public void DeleteAccountsForMonth(int year, int month)
{
var result = from acm in this._database.AccountsOnMonth
where ((acm.Year == year) && (acm.Month == month))
select acm.Id;
var query = (ObjectQuery<int>)result;
string sql = string.Format(
"DELETE FROM [AccountsOnMonth] WHERE [AccountsOnMonth].[Id] IN ({0})",
query.ToTraceString()
);
var parameters = new List<System.Data.SqlClient.SqlParameter>();
foreach (ObjectParameter parameter in query.Parameters)
{
parameters.Add(new System.Data.SqlClient.SqlParameter {
ParameterName = parameter.Name,
Value = parameter.Value
});
}
this._database.Database.ExecuteSqlCommand(sql, parameters.ToArray());
}
Basically, what I'm trying to do is to delete a bulk of data from a context (get a query result, get SQL and execute it). 基本上,我要做的是从上下文中删除大量数据(获取查询结果,获取SQL并执行它)。 But I'm having a problem when casting
result
to ObjectQuery
. 但是在将
result
为ObjectQuery
时遇到问题。 The exception that gives is 给出的例外是
Unable to cast object of type 'System.Data.Entity.Infrastructure.DbQuery
1[System.Int32]' to type 'System.Data.Objects.ObjectQuery
1[System.Int32]'.无法转换类型为“System.Data.Entity.Infrastructure.DbQuery
1[System.Int32]' to type 'System.Data.Objects.ObjectQuery
1 [System.Int32]”。
Can anybody give any hint to solve this? 任何人都可以提供任何解决方案吗? Thanks!
谢谢!
EDIT: Ladislav first solution helped me solve the problem, but it happenned a little problem with the SQL parameters of the generated SQL query, ie the SQL query generated by query.ToString()
was this: 编辑: Ladislav第一个解决方案帮助我解决了这个问题,但是生成的SQL查询的SQL参数出现了一点问题,即
query.ToString()
生成的SQL查询是这样的:
DELETE FROM [SncAccountOnMonths] WHERE [SncAccountOnMonths].[Id] IN (
SELECT [Extent1].[Id] AS [Id]
FROM [dbo].[SncAccountOnMonths] AS [Extent1]
WHERE ([Extent1].[Year] = @p__linq__0) AND ([Extent1].[Month] = @p__linq__1))
The problem was that the variables @p__linq__0
and @p__linq__1
where not declared and so the query gave the error "Must declare the scalar variable @p_ linq _0" (I sure it would give the same error for variable @p__linq__1
). 问题是变量
@p__linq__0
和@p__linq__1
未声明,因此查询给出错误“必须声明标量变量@p_ linq _0”(我确定它会给变量@p__linq__1
带来相同的错误)。 To "declare" them I need to pass them as arguments of the ExecuteSqlCommand()
. 要“声明”它们,我需要将它们作为
ExecuteSqlCommand()
参数传递。 And so, the final solution for the initial answer is the code below: 因此,初始答案的最终解决方案是以下代码:
public void DeleteAccountsForMonth(int year, int month)
{
var result = (this._database.AccountsOnMonth
.Where(acm => (acm.Year == year) && (acm.Month == month)))
.Select(acm => acm.Id);
var query = (DbQuery<int>)result;
string sql = string.Format(
"DELETE FROM [AccountsOnMonth] WHERE [AccountsOnMonth].[Id] IN ({0})",
query.ToString()
);
this._database.Database.ExecuteSqlCommand(sql,
new SqlParameter("p__linq__0", year),
new SqlParameter("p__linq__1", month)
);
}
By the way, I assume the variables generated always have the format @p__linq__
, unless Microsoft's Entity Framework Team changes it in any future EF update... 顺便说一句,我假设生成的变量总是具有
@p__linq__
格式,除非Microsoft的实体框架团队在任何未来的EF更新中更改它...
That is because your _database
is derived from DbContext
and your AccountsOfMonth
is DbSet<>
. 这是因为您的
_database
是从DbContext
派生的,而您的AccountsOfMonth
是DbSet<>
。 In such case you cannot use ObjectQuery
directly because DbSet<>
produces DbQuery<>
which is not convertible to ObjectQuery<>
. 在这种情况下,您不能直接使用
ObjectQuery
,因为DbSet<>
生成DbQuery<>
,它不能转换为ObjectQuery<>
。
You must either use DbQuery<>
directly: 您必须直接使用
DbQuery<>
:
var result = from acm in this._database.AccountsOnMonth
where ((acm.Year == year) && (acm.Month == month))
select acm.Id;
var query = (DbQuery<int>)result;
string sql = string.Format(
"DELETE FROM [AccountsOnMonth] WHERE [AccountsOnMonth].[Id] IN ({0})",
query.ToString()
);
Or you must first convert your context to ObjectContext
and create ObjectSet<>
: 或者您必须首先将您的上下文转换为
ObjectContext
并创建ObjectSet<>
:
var objectContext = ((IObjectContextAdapter)_database).ObjectContext;
var set = objectContext.CreateObjectSet<AccountsOnMonth>();
var resut = from acm in set
where ((acm.Year == year) && (acm.Month == month))
select acm.Id;
The problem with first approach is that DbQuery
doesn't offer Parameters
collection - just another example of simplification in DbContext API which only makes it harder to use. 第一种方法的问题是
DbQuery
不提供Parameters
集合 - 只是DbContext API中的另一个简化示例,它只会使其更难使用。
In my case I really needed the parameters and I found this workaround: 在我的情况下,我真的需要参数,我发现这个解决方法:
var query = (DbQuery<int>)result;
FieldInfo internalQueryField = query.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance).Where(f => f.Name.Equals("_internalQuery")).FirstOrDefault();
var internalQuery = internalQueryField.GetValue(query);
FieldInfo objectQueryField = internalQuery.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance).Where(f => f.Name.Equals("_objectQuery")).FirstOrDefault();
ObjectQuery<int> objectQuery = objectQueryField.GetValue(internalQuery) as ObjectQuery<int>;
foreach (ObjectParameter objectParam in objectQuery.Parameters)
{
SqlParameter sqlParam = new SqlParameter(objectParam.Name, objectParam.Value);
// Etc...
}
I'm implementing SqlCacheDependency with Entity Framework. 我正在使用Entity Framework实现SqlCacheDependency。 :-)
:-)
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.