Should we add Entity Framework dll to all layers - entity-framework

Question

I am writing a test app using EF code first. I have distributed code among different layers. I thought I would have to install the entity framework package to the data access layer only but what I ended up with is installing the package (adding dlls) to all the layers namely UI, BLL, Models, DAL. Is this okay or I am doing something wrong. Below is sample code to give you an idea of what I am trying to do
Model Layer
This layer is reference in all other layers/projects
namespace Model
{
Public class Sample
{
[ForeignKey("Sample2Id")]
...
}
}
In this layer I had to use Entity Framework dlls because of Data Annotation like [ForeignKey..
DAL
namespace DAL
{
public class SampleContext:DbContext
{
...
}
}
In DAL I only have the context class and migrations
BLL
namespace BLL
{
public class SampleBLL
{
public List<Sample> GetAll()
{
retrn new SampleContext().Samples().ToList()
}
}
}
If I uninstall EF for BLL I get the following error
The type System.Data.Entity.DbContext is defined in an assembly that is not referenced.
UI
namespace UI
{
public class UIHelper
{
public List<Sample> GetSamples()
{
return new SampleBLL().GetAll();
}
}
}
If I uninstall the EF package from UI I get the following error
The Entity Framework provider type
'System.Data.Entity.SqlServer.SqlProviderServices,
EntityFramework.SqlServer' registered in the application config file
for the ADO.NET provider with invariant name 'System.Data.SqlClient'
could not be loaded. Make sure that the assembly-qualified name is
used and that the assembly is available to the running application

Answer 1

I created a sample project which is quite similar to your current setup minus the Model Layer/DAL separation.
I have three projects, DAL (which contains references to the EntityFramework.dll and the EntityFramework.SqlServer.dll), BLL which just calls a method in the DAL, and the UI which just calls the BLL methods.
I had to add the <configSections>, the <entityFramework>, and the <connectionStrings> portions of the app.config of the DAL into the UI's app.config.
When I ran the code the first time, I ran into the same error you ran into. So I looked into the debug folder of my UI Project and noticed that the EntityFramework.dll was copied into the folder due to the DAL's dependency on it. I also noticed that the EntityFramework.SqlServer.dll was NOT copied into the debug folder despite the DAL also having a dependency on it.
I copied the EntityFramework.SqlServer.dll into the debug folder of the UI Project then re-ran the project then, Viola! My code ran as expected.
It looks like the problem here is that one dll is not being copied into the UI Project debug folder as it is expected to.