The type or namespace name 'Objects' does not exist in the namespace 'System.Data'

问题

I am using entities, C# and SQL Server to create an n-tier app. I am creating some base classes common to all my DAL components. In this base class, i want to handle the connection state of the ObjectContext base class inherited by entities object.

Compiling throws the following error:

The type or namespace name 'Objects' does not exist in the namespace 'System.Data' (are you missing an assembly reference?)

Also, the using statement System.Data.Objects doesn't resolve for the same reason.

I tried adding the assembly as reference, but couldn't find it in the .NET tab of assembly references.

Any thoughts? Thanks!

回答1:

You need to add a reference to the .NET assembly System.Data.Entity.dll.

回答2:

If you are using Entity Framework 6, the name space has changed. You want to use

System.Data.Entity.Core.Objects.ObjectQuery

回答3:

Upgraded from EF5 to EF6 nuget a while back and kept encountering this issue. I'd temp fix it by updating the generated code to reference System.Data.Entity.Core.Objects, but after generation it would be changed back again (as expected since its generated).

This solved the problem for good:

http://msdn.microsoft.com/en-us/data/upgradeef6

If you have any models created with the EF Designer, you will need to update the code generation templates to generate EF6 compatible code. Note: There are currently only EF 6.x DbContext Generator templates available for Visual Studio 2012 and 2013.

Delete existing code-generation templates. These files will typically be named <edmx_file_name>.tt and <edmx_file_name>.Context.tt and be nested under your edmx file in Solution Explorer. You can select the templates in Solution Explorer and press the Del key to delete them.
Note: In Web Site projects the templates will not be nested under your edmx file, but listed alongside it in Solution Explorer.
Note: In VB.NET projects you will need to enable 'Show All Files' to be able to see the nested template files.

Add the appropriate EF 6.x code generation template. Open your model in the EF Designer, right-click on the design surface and select Add Code Generation Item...
If you are using the DbContext API (recommended) then EF 6.x DbContext Generator will be available under the Data tab.
Note: If you are using Visual Studio 2012, you will need to install the EF 6 Tools to have this template. See Get Entity Framework for details.

If you are using the ObjectContext API then you will need to select the Online tab and search for EF 6.x EntityObject Generator.

If you applied any customizations to the code generation templates you will need to re-apply them to the updated templates.

回答4:

Same problem in VS 2013

I added in Web.config :

<add assembly="System.Data.Entity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />

It worked like a charm.

I found it on page: http://www.programmer.bz/Home/tabid/115/asp_net_sql/281/The-type-or-namespace-name-Objects-does-not-exist-in-the-namespace-SystemData.aspx

回答5:

In my case for EF 6+, when using this:

System.Data.Entity.Core.Objects.ObjectQuery

As part of this command:

var sql = ((System.Data.Entity.Core.Objects.ObjectQuery)query).ToTraceString();

I got this error:

Cannot cast 'query' (which has an actual type of 'System.Data.Entity.Infrastructure.DbQuery<<>f__AnonymousType3<string,string,string,short,string>>') to 'System.Data.Entity.Core.Objects.ObjectQuery'

So I ended up having to use this:

var sql = ((System.Data.Entity.Infrastructure.DbQuery<<>f__AnonymousType3<string,string,string,short,string>>)query).ToString();

Of course your anonymous type signature might be different.

HTH.

回答6:

if you want to use "System.Data.Objects.EntityFunctions"

use "System.Data.Entity.DbFunctions" in EF 6.1+

回答7:

I added a reference to the .dll file, for System.Data.Linq, the above was not sufficient. You can find .dll in the various directories for the following versions.

System.Data.Linq C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\v3.5\System.Data.Linq.dll 3.5.0.0

System.Data.Linq C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework.NETFramework\v4.0\Profile\Client\System.Data.Linq.dll 4.0.0.0