In version 3.1 of the book (updated on the 22 of November), there seems to be an error in Chapter 2(page 45).
Make sure you still have Bow_Ties.xcdatamodeld open, select the
Bowtiesentity
and open the Data Model inspector. Set the Codegen dropdown to Manual/None,
as shown below:
The above paragraph fails to mention to set the module option to Current Product Module. Without doing this, Xcode 8.1 says that Bowtie is ambiguous and the project doesn’t compile.
Bowtie also suddenly becomes Bowties in the both the above paragraph and in the screenshot in the book.
This is how it should look to work, like in the final version of this project 
The project compiles for me after fixing this error.
The same error still happens in Chapter 3 and is fixed in the same way. Dog and Walk’s module should be set to Current Product Module.