I am building an ASP.NET Web Forms web site using .NET 4.5.
The error ...
The type 'System.ComponentModel.DataAnnotations.Schema.ForeignKeyAttribute' exists in both 'f:\Projects\web sites\RC1Iteration05\packages\EntityFramework.5.0.0\lib\net40\EntityFramework.dll' and 'c:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5\System.ComponentModel.DataAnnotations.dll'
I have tried to alias the libraries using ...
csc /r:EF_DataAnnotations="f:\Projects\web sites\RC1Iteration05\packages\EntityFramework.5.0.0\lib\net40\EntityFramework.dll" /r:CM_DataAnnotations="c:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5\System.ComponentModel.DataAnnotations.dll"
but this only resulted in "No Source File specified" which is equally confusing since the source files were specified as directed (here & here).
I did notice that the error was referencing the EF dll in the net40 folder rather than the net45 folder. I figure if I used the net45 version the problem would resolve itself, however I do not know how to change that reference. I changed the "targetFramework" attribute to the EntityFramework package in the packages.config file, but that did not make any difference.
I am a bit stuck since both of the solutions did not seem to do anything.
I looked around and found a number of posts here where folks have dealt with similar issues but have received no responses. I am hoping that there is someone out there who can help!
Thanks
G
As you noticed, you're using the .Net 4.0 version of Entity Framework on .Net 4.5.
That won't work.
Re-install EF from NuGet and it should work fine.
The other options didn't work for me. What did work was going into \packages\EntityFramework.6.1.3\lib\ and deleting the net40 directory and then doing a rebuild all.
来源：https://stackoverflow.com/questions/17791930/type-definition-exists-in-two-libraries