If you use Entity Framework in Sharepoint (I described one useful technique which simplifies usage of EF in Sharepoint in this article: Build connection string for Entity Framework programmatically via code or use Entity Framework in Sharepoint Timer jobs) you may face with the following error:
The EntityContainer name must be unique. An EntityContainer with the name '…' is already defined
Although in your project (class library which you install to GAC for using it in Sharepoint) there is single entity container with specified name.
The problem is that entity container name appears to be unique within project boundaries. I.e. if you have another project which is compiled and installed to the GAC and loaded to the same app domain and which uses the same metadata for Entity Framework data model like:
and then install another assembly to the GAC with the same EF data model metadata – you will get the above error when second project will be loaded to Sharepoint site’s app domain. This is not that obvious that you have to use unique name for EF entity containers across all assemblies used in Sharepoint. Solution for this problem is to rename EF data model in second project so it will have unique name:
After that your code will start working in Shrepoint.