Add a unique index to genres.name.

migration/20180202-genre-name-is-unique.sql

@@ -0,0 +1,10 @@
+-- genres.name should be indexed and unique.
+DO $$ 
+    BEGIN
+        BEGIN
+create unique index ix_genres_name on genres (name);
+        EXCEPTION
+            WHEN OTHERS THEN RAISE NOTICE 'WARNING: it looks like ix_genres_name already exists; it was probably created on initial database creation.';
+        END;
+    END;
+$$;

model.py

@@ -5876,7 +5876,7 @@ class Genre(Base, HasFullTableCache):
     """
     __tablename__ = 'genres'
     id = Column(Integer, primary_key=True)
-    name = Column(Unicode)
+    name = Column(Unicode, unique=True, index=True)
 
     # One Genre may have affinity with many Subjects.
     subjects = relationship("Subject", backref="genre")
@@ -8708,7 +8708,7 @@ def cautious_http_get(cls, url, headers, **kwargs):
 
     # Sites that cause problems for us if we make automated
     # HTTP requests to them while trying to find free books.
-    AVOID_WHEN_CAUTIOUS_DOMAINS = ['gutenberg.org']
+    AVOID_WHEN_CAUTIOUS_DOMAINS = ['gutenberg.org', 'books.google.com']
 
     @classmethod
     def get_would_be_useful(

tests/test_model.py

@@ -917,7 +917,14 @@ def exploding_create_hook():
         # No exception.
         eq_(drama, drama2)
         eq_(False, is_new)
-
+
+    def test_name_is_unique(self):
+        g1, ignore = Genre.lookup(self._db, "A Genre", autocreate=True)
+        g2, ignore = Genre.lookup(self._db, "A Genre", autocreate=True)
+        eq_(g1, g2)
+
+        assert_raises(IntegrityError, create, self._db, Genre, name="A Genre")
+
     def test_default_fiction(self):
         sf, ignore = Genre.lookup(self._db, "Science Fiction")
         nonfiction, ignore = Genre.lookup(self._db, "History")