同时使用实体框架与SQL Server和SQLite数据库

I have a C# .Net 4.0 console application for testing purposes (using VS 2012). My aim is to be able to create a single Entity Framework .edmx file that can be used on both an MS SQL Server database, and an SQLite database. Basically, I want to use the same entity model classes and collections for querying, but easily be able to switch between the two different databases at will.

我有一个用于测试目的的C＃.Net 4.0控制台应用程序（使用VS 2012）。我的目标是能够创建一个可以在MS SQL Server数据库和SQLite数据库上使用的单个Entity Framework .edmx文件。基本上，我想使用相同的实体模型类和集合进行查询，但很容易就能随意在两个不同的数据库之间切换。

So far I have created my .edmx file by connection to MS Server database and adding my single test table (called Contact). With this I can then use the following code to get data from my table:

到目前为止，我已经通过连接到MS Server数据库并添加了我的单个测试表（称为Contact）来创建我的.edmx文件。有了这个，我可以使用以下代码从我的表中获取数据：

var db = new DataAccess.ContactTestEntities();
foreach (var contact in db.Contacts)
    Console.WriteLine("" + contact.ID + ". " + contact.FirstName + " " + contact.LastName);

Now, I want to be able to use the same code but connect to an SQLite database instead. I have written a partial class that allows my to change the connection string on contruction like so:

现在，我希望能够使用相同的代码，而是连接到SQLite数据库。我编写了一个部分类，允许我更改contruction上的连接字符串，如下所示：

var db = new DataAccess.ContactTestEntities("MY SQLITE CONNECTION STRING");

It works fine in that respect except when trying to query the database I get this error:

它在这方面工作正常，除了在尝试查询数据库时我收到此错误：

Unable to cast object of type 'System.Data.SQLite.SQLiteConnection' to type 'System.Data.SqlClient.SqlConnection'.

无法将类型为“System.Data.SQLite.SQLiteConnection”的对象强制转换为“System.Data.SqlClient.SqlConnection”。

I have tried to find a solution to this but have hit a dead end and I am struggling to find the next step to take.

我试图找到解决方案，但已经走到了尽头，我正在努力寻找下一步。

So that is my question: How can I get past this problem? Or is there another approach I can take to get the same desired results?

这就是我的问题：我怎样才能解决这个问题？或者我可以采取另一种方法来获得相同的预期结果？

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Stack Trace for above exception:

堆栈跟踪以上异常：

at System.Data.SqlClient.SqlCommand.set_DbConnection(DbConnection value) at System.Data.Common.Utils.CommandHelper.SetStoreProviderCommandState(EntityCommand entityCommand, EntityTransaction entityTransaction, DbCommand storeProviderCommand) at System.Data.EntityClient.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior) at System.Data.Objects.Internal.ObjectQueryExecutionPlan.Execute[TResultType](ObjectContext context, ObjectParameterCollection parameterValues) at System.Data.Objects.ObjectQuery1.GetResults(Nullable1 forMergeOption) at System.Data.Objects.ObjectQuery1.System.Collections.Generic.IEnumerable<T>.GetEnumerator() at System.Data.Entity.Internal.Linq.InternalQuery1.GetEnumerator()
at System.Data.Entity.Internal.Linq.InternalSet1.GetEnumerator()
at System.Data.Entity.Infrastructure.DbQuery1.System.Collections.Generic.IEnumerable.GetEnumerator() at SQLiteTest.Program.ReadFromSqlite() in c:\Development\Projects\Test Applications\SQLiteTest\SQLiteTest\Program.cs:line 82 at SQLiteTest.Program.ReadTests() in c:\Development\Projects\Test Applications\SQLiteTest\SQLiteTest\Program.cs:line 63 at SQLiteTest.Program.ProcessMenu() in c:\Development\Projects\Test Applications\SQLiteTest\SQLiteTest\Program.cs:line 36 at SQLiteTest.Program.Main(String[] args) in c:\Development\Projects\Test Applications\SQLiteTest\SQLiteTest\Program.cs:line 14 at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart()

处于System.Data.Ents.Clmand.AntityClient.EntityCommandDefinition.ExecuteStoreCommands的System.Data.Common.Utils.CommandHelper.SetStoreProviderCommandState（EntityCommand entityCommand，EntityTransaction entityTransaction，DbCommand storeProviderCommand）中的System.Data.SqlClient.SqlCommand.set_DbConnection（DbConnection值）（EntityCommand entityCommand， SystemB上的System.Data.Objects.Internal.ObjectQueryExecutionPlan.Execute [TResultType]（ObjectContext context，ObjectParameterCollection parameterValues）中的System.Data.Objects.1.EetRetults（Nullable1 forMergeOption）处于System.Data.Objects.ObjectQuery1.System的CommandBehavior行为。 System.Data.Entity上的System.Data.Entity.Internal.Linq.InternalSet1.GetEnumerator（）中System.Data.Entity.Internal.Linq.InternalQuery1.GetEnumerator（）的Collections.Generic.IEnumerable .GetEnumerator（） .Inbase的基础设施.DbQuery1.System.Collections.Generic.IEnumerable.GetEnumerator（），位于c：\ Development \ Projects \ Test Applications \ SQ中的SQLiteTest.Program.ReadFromSqlite（） LiteTest \ SQLiteTest \ Program.cs：位于c：\ Development \ Projects \ Test Applications \ SQLiteTest \ SQLiteTest \ Program.cs中的SQLiteTest.Program.ReadTests（）中的第82行：位于c中的SQLiteTest.Program.ProcessMenu（）中的第63行： \ Development \ Projects \ Test Applications \ SQLiteTest \ SQLiteTest \ Program.cs：第13行，位于c：\ Development \ Projects \ Test Applications \ SQLiteTest \ SQLiteTest \ Program.cs中的SQLiteTest.Program.Main（String [] args）：line 14位于System.TereadingStudio上的System.AppDomain._nExecuteAssembly（RuntimeAssembly assembly，String [] args），System.Threading.ExecutionContext.RunInternal（ExecutionContext executionContext，ContextCallback callback，Object state，Boolean preserveSyncCtx）中的Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly（）在System.Threading.ThreadHelper.Thre的System.Threading.ExecutionContext.Run（ExecutionContext executionContext，ContextCallback回调，对象状态）中的System.Threading.ExecutionContext.Run（ExecutionContext executionContext，ContextCallback回调，Object状态，Boolean preserveSyncCtx） adStart（）

1 个解决方案

#1

Are you passing in the connection string or the name of the connection string in the <connectionStrings> app settings section? I believe the issue is as you describe. It defaults the provider to System.Data.SqlClient. If you want Sql Lite, you have to set the providerName on the <connectionString> and then send the name (attribute) of that <connectionString> to DbContext (It knows how to look that up automatically). It should then use that new providerName attribute instead of SqlClient.

您是否在 应用程序设置部分中传递连接字符串或连接字符串的名称？我相信问题就像你描述的那样。它将提供程序默认为System.Data.SqlClient。如果你想要Sql Lite，你必须在 上设置providerName，然后将该 的名称（属性）发送给DbContext（它知道如何自动查找）。然后它应该使用新的providerName属性而不是SqlClient。