First changed so that it doesn't check that it is the only row. Old behaviour is now in the new method 'one()' instead. 'scalar' uses old behaviour still

records.py

@@ -208,6 +208,27 @@ class RecordCollection(object):
         `default` is an instance or subclass of Exception, then raise it
         instead of returning it."""
 
+        # Try to get a record, or return/raise default.
+        try:
+            record = self[0]
+        except IndexError:
+            if isexception(default):
+                raise default
+            return default
+
+        # Cast and return.
+        if as_dict:
+            return record.as_dict()
+        elif as_ordereddict:
+            return record.as_dict(ordered=True)
+        else:
+            return record
+
+    def one(self, default=None, as_dict=False, as_ordereddict=False):
+        """Returns a single record for the RecordCollection, ensuring that it
+        is the only record, or returns `default`. If `default` is an instance
+        or subclass of Exception, then raise it instead of returning it."""
+
         # Try to get a record, or return/raise default.
         try:
             record = self[0]
@@ -234,8 +255,8 @@ class RecordCollection(object):
 
     def scalar(self, default=None):
         """Returns the first column of the first row, or `default`."""
-        first = self.first()
-        return first[0] if first else default
+        row = self.one()
+        return row[0] if row else default
 
 
 class Database(object):

tests/test_records.py

@@ -72,10 +72,6 @@ class TestRecordCollection:
         rows = records.RecordCollection(iter([]))
         assert rows.first('Cheese') == 'Cheese'
 
-    def test_first_raises_when_more_than_first(self):
-        rows = records.RecordCollection(IdRecord(i) for i in range(3))
-        raises(ValueError, rows.first)
-
     def test_first_raises_default_if_its_an_exception_subclass(self):
         rows = records.RecordCollection(iter([]))
         class Cheese(Exception): pass
@@ -86,6 +82,34 @@ class TestRecordCollection:
         class Cheese(Exception): pass
         raises(Cheese, rows.first, Cheese('cheddar'))
 
+    # one
+
+    def test_one_returns_a_single_record(self):
+        rows = records.RecordCollection(IdRecord(i) for i in range(1))
+        assert rows.one() == IdRecord(0)
+
+    def test_one_defaults_to_None(self):
+        rows = records.RecordCollection(iter([]))
+        assert rows.one() is None
+
+    def test_one_default_is_overridable(self):
+        rows = records.RecordCollection(iter([]))
+        assert rows.one('Cheese') == 'Cheese'
+
+    def test_one_raises_when_more_than_one(self):
+        rows = records.RecordCollection(IdRecord(i) for i in range(3))
+        raises(ValueError, rows.one)
+
+    def test_one_raises_default_if_its_an_exception_subclass(self):
+        rows = records.RecordCollection(iter([]))
+        class Cheese(Exception): pass
+        raises(Cheese, rows.one, Cheese)
+
+    def test_one_raises_default_if_its_an_exception_instance(self):
+        rows = records.RecordCollection(iter([]))
+        class Cheese(Exception): pass
+        raises(Cheese, rows.one, Cheese('cheddar'))
+
     # scalar
 
     def test_scalar_returns_a_single_record(self):
@@ -100,7 +124,7 @@ class TestRecordCollection:
         rows = records.RecordCollection(iter([]))
         assert rows.scalar('Kaffe') == 'Kaffe'
 
-    def test_scalar_raises_when_more_than_first(self):
+    def test_scalar_raises_when_more_than_one(self):
         rows = records.RecordCollection(IdRecord(i) for i in range(3))
         raises(ValueError, rows.scalar)