Add pgt_force_defaults method for forcing default values during inserts

Author: jeremyevans

README.rdoc

@@ -198,6 +198,21 @@ Options:
 :referenced_function_name :: function name for trigger function on referenced table
 :referenced_trigger_name :: trigger name for referenced table
 
+=== Force Defaults - pgt_force_defaults
+
+This takes 2 arguments, a table and a hash of column default values, and sets
+up an insert trigger that will override user submitted or database
+default values and use the values given when setting up the trigger.
+This is mostly useful in situations where multiple database accounts
+are used where one account has insert permissions but not update
+permissions, and you want to ensure that inserted rows have specific
+column values to enforce security requirements.
+
+Arguments:
+table :: The name of the table
+defaults :: A hash of default values to enforce, where keys are column names
+            and values are the default values to enforce
+
 == License
 
 This library is released under the MIT License.  See the MIT-LICENSE

lib/sequel/extensions/pg_triggers.rb

@@ -51,6 +51,21 @@ def pgt_created_at(table, column, opts={})
         SQL
       end
 
+      def pgt_force_defaults(table, defaults, opts={})
+        cols = defaults.keys.sort.join('_')
+        trigger_name = opts[:trigger_name] || "pgt_fd_#{cols}"
+        function_name = opts[:function_name] || "pgt_fd_#{table}__#{cols}"
+        lines = defaults.map do |column, v|
+          "NEW.#{quote_identifier(column)} = #{literal(v)};"
+        end
+        pgt_trigger(table, trigger_name, function_name, [:insert], <<-SQL)
+        BEGIN
+          #{lines.join("\n")}
+          RETURN NEW;
+        END;
+        SQL
+      end
+
       def pgt_immutable(table, *columns)
         opts = columns.last.is_a?(Hash) ? columns.pop : {}
         trigger_name = opts[:trigger_name] || "pgt_im_#{columns.join('__')}"

spec/sequel_postgresql_triggers_spec.rb

@@ -584,3 +584,26 @@
     DB[:accounts].delete
   end
 end
+
+describe "PostgreSQL Force Defaults Trigger" do
+  before do
+    DB.create_table(:accounts){integer :id; integer :a, :default=>0; String :b; integer :c; integer :d, :default=>4}
+    DB.pgt_force_defaults(:accounts, {:a=>1, :b=>"'\\a", :c=>nil}, :function_name=>:spgt_force_defaults)
+    @ds = DB[:accounts]
+  end
+
+  after do
+    DB.drop_table(:accounts)
+    DB.drop_function(:spgt_force_defaults)
+  end
+
+  it "should override default values when inserting" do
+    @ds.insert
+    DB[:accounts].first.must_equal(:id=>nil, :a=>1, :b=>"'\\a", :c=>nil, :d=>4)
+
+    @ds.delete
+    @ds.insert(:id=>10, :a=>11, :b=>12, :c=>13, :d=>14)
+    DB[:accounts].first.must_equal(:id=>10, :a=>1, :b=>"'\\a", :c=>nil, :d=>14)
+  end
+end
+