Fix db:seed:export task

* replace variable names with Hash to avoid invalid Ruby identifiers
* export all values as single-quoted to avoid string interpolation and
  treating BigDecimal numbers as Float
* #truncate table instead of #delete_all to avoid foreing_key
  constraints errors

Closes #56

db/seeds.rb

@@ -20,4 +20,6 @@ end
 # Formulas will be deleted as dependent on Quantities
 #[Source, Quantity, Unit].each { |model| model.defaults.delete_all }
 
-require 'seeds/units.rb'
+# To clear contents of the table, use #truncate instead of #delete_all. This
+# avoids foreign_key constraints errors.
+require_relative 'seeds/units.rb'

db/seeds/templates/units.erb

@@ -1,9 +1,9 @@
 Unit.transaction do
-  Unit.defaults.delete_all
+  ActiveRecord::Base.connection.truncate(Unit.table_name)
 <% Unit.defaults.ordered.each do |unit| %>
 <%= "\n" if unit.base.nil? %>
-  unit_<%= unit.symbol %> =
-    Unit.create symbol: "<%= unit.symbol %>",<% unless unit.base.nil? %> base: unit_<%= unit.base.symbol %>, multiplier: <%= unit.multiplier.to_scientific %>,<% end %>
-                description: "<%= unit.description %>"
+  units['<%= unit.symbol %>'] =
+    Unit.create symbol: '<%= unit.symbol %>',<% unless unit.base.nil? %> base: units['<%= unit.base.symbol %>'], multiplier: '<%= unit.multiplier.to_scientific %>',<% end %>
+                description: '<%= unit.description %>'
 <% end %>
 end

db/seeds/units.rb

@@ -1,36 +1,36 @@
 Unit.transaction do
-  Unit.defaults.delete_all
+  ActiveRecord::Base.connection.truncate(Unit.table_name)
 
-  unit_1 =
-    Unit.create symbol: "1",
-                description: "dimensionless, one"
-  unit_ppm =
-    Unit.create symbol: "ppm", base: unit_1, multiplier: 1e-6,
-                description: "parts per million"
-  unit_‱ =
-    Unit.create symbol: "‱", base: unit_1, multiplier: 1e-4,
-                description: "basis point"
-  unit_‰ =
-    Unit.create symbol: "‰", base: unit_1, multiplier: 1e-3,
-                description: "promille"
-  unit_% =
-    Unit.create symbol: "%", base: unit_1, multiplier: 1e-2,
-                description: "percent"
+  units['1'] =
+    Unit.create symbol: '1',
+                description: 'dimensionless, one'
+  units['ppm'] =
+    Unit.create symbol: 'ppm', base: units['1'], multiplier: '1e-6',
+                description: 'parts per million'
+  units['‱'] =
+    Unit.create symbol: '‱', base: units['1'], multiplier: '1e-4',
+                description: 'basis point'
+  units['‰'] =
+    Unit.create symbol: '‰', base: units['1'], multiplier: '1e-3',
+                description: 'promille'
+  units['%'] =
+    Unit.create symbol: '%', base: units['1'], multiplier: '1e-2',
+                description: 'percent'
 
-  unit_g =
-    Unit.create symbol: "g",
-                description: "gram"
-  unit_ug =
-    Unit.create symbol: "ug", base: unit_g, multiplier: 1e-6,
-                description: "microgram"
-  unit_mg =
-    Unit.create symbol: "mg", base: unit_g, multiplier: 1e-3,
-                description: "milligram"
-  unit_kg =
-    Unit.create symbol: "kg", base: unit_g, multiplier: 1e3,
-                description: "kilogram"
+  units['g'] =
+    Unit.create symbol: 'g',
+                description: 'gram'
+  units['µg'] =
+    Unit.create symbol: 'µg', base: units['g'], multiplier: '1e-6',
+                description: 'microgram'
+  units['mg'] =
+    Unit.create symbol: 'mg', base: units['g'], multiplier: '1e-3',
+                description: 'milligram'
+  units['kg'] =
+    Unit.create symbol: 'kg', base: units['g'], multiplier: '1e3',
+                description: 'kilogram'
 
-  unit_kcal =
-    Unit.create symbol: "kcal",
-                description: "kilocalorie"
+  units['kcal'] =
+    Unit.create symbol: 'kcal',
+                description: 'kilocalorie'
 end

lib/core_ext/active_model/validations/numericality_validates_precision_and_scale.rb

@@ -4,6 +4,9 @@ module CoreExt::ActiveModel::Validations::NumericalityValidatesPrecisionAndScale
 
     if options[:precision] || options[:scale]
       attr_type = record.class.type_for_attribute(attr_name)
+      # For conversion of 'value' to BigDecimal 'ndigits' is not supplied intentionally,
+      # to avoid silent rounding. It is only required for conversion from Float and
+      # Rational, which should not happen.
       value = BigDecimal(value) unless value.is_a? BigDecimal
       if options[:precision] && (value.precision > attr_type.precision)
         record.errors.add(attr_name, :precision_exceeded, **filtered_options(attr_type.precision))