Fixed taking precision into count when assigning a value to timestamp attribute

Timestamp column can have less precision than ruby timestamp
In result in how big a fraction of a second can be stored in the
database.

  m = Model.create!
  m.created_at.usec == m.reload.created_at.usec
    # => false
    # due to different seconds precision in Time.now and database column

If the precision is low enough, (mysql default is 0, so it is always low
enough by default) the value changes when model is reloaded from the
database. This patch fixes that issue ensuring that any timestamp
assigned as an attribute is converted to column precision under the
attribute.

2 files changed, 12 insertions, 9 deletions

diff --git a/activemodel/lib/active_model/type/date_time.rb b/activemodel/lib/active_model/type/date_time.rb
index b068cfc672..2f2df4320f 100644
--- a/activemodel/lib/active_model/type/date_time.rb
+++ b/activemodel/lib/active_model/type/date_time.rb
@@ -12,11 +12,11 @@ module ActiveModel
 
       private
 
-      def cast_value(string)
-        return string unless string.is_a?(::String)
-        return if string.empty?
+      def cast_value(value)
+        return apply_seconds_precision(value) unless value.is_a?(::String)
+        return if value.empty?
 
-        fast_string_to_time(string) || fallback_string_to_time(string)
+        fast_string_to_time(value) || fallback_string_to_time(value)
       end
 
       # '0.123456' -> 123456
diff --git a/activemodel/lib/active_model/type/helpers/time_value.rb b/activemodel/lib/active_model/type/helpers/time_value.rb
index 0a0e58654b..63993c0d93 100644
--- a/activemodel/lib/active_model/type/helpers/time_value.rb
+++ b/activemodel/lib/active_model/type/helpers/time_value.rb
@@ -5,11 +5,7 @@ module ActiveModel
     module Helpers
       module TimeValue # :nodoc:
         def serialize(value)
-          if precision && value.respond_to?(:usec)
-            number_of_insignificant_digits = 6 - precision
-            round_power = 10 ** number_of_insignificant_digits
-            value = value.change(usec: value.usec / round_power * round_power)
-          end
+          value = apply_seconds_precision(value)
 
           if value.acts_like?(:time)
             zone_conversion_method = is_utc? ? :getutc : :getlocal
@@ -34,6 +30,13 @@ module ActiveModel
           end
         end
 
+        def apply_seconds_precision(value)
+          return value unless precision && value.respond_to?(:usec)
+          number_of_insignificant_digits = 6 - precision
+          round_power = 10 ** number_of_insignificant_digits
+          value.change(usec: value.usec / round_power * round_power)
+        end
+
         def type_cast_for_schema(value)
           "'#{value.to_s(:db)}'"
         end