Question

How would I set the description property of a field in the SQL Server database from an Entity Framework code-first project?

Answer 1

You would not unless you create custom initializer and in its Seed method you will insert a new record to sys.extended_properties for each single column where you want a description. You can use system stored procedure for that

EXEC sys.sp_addextendedproperty @name='MS_Description', 
                                @value=N'Your description', 
                                @level0type=N'SCHEMA',@level0name=N'YourSchema', 
                                @level1type=N'TABLE',@level1name=N'YourTable', 
                                @level2type=N'COLUMN',@level2name=N'YourColumn'