Upgrade from SQL Server 2008 R2 to SQL Server 2012

Hello,

We are planning on upgrading from SQL Server 2008 R2 SE to SQl Server 2012 in a couple of months.  I was wondering what code changes are required at the developer's end. Currently our developers use EDMX. Is there a url that can point me to what code changes are required and what breaks if we upgrade this?

Thanks