Honor configured :top option for empty lists

lib/sequel/plugins/list.rb

@@ -185,10 +185,13 @@ def prev(n = 1)
  end
 
  # Set the value of the position_field to the maximum value plus 1 unless the
- # position field already has a value.
+ # position field already has a value. If the list is empty, the position will
+ # be set to the model's +top_of_list+ value.
  def before_validation
  unless get_column_value(position_field)
- set_column_value("#{position_field}=", list_dataset.max(position_field).to_i+1)
+ current_max = list_dataset.max(position_field)
+ value = current_max.nil? ? model.top_of_list : current_max.to_i + 1
+ set_column_value("#{position_field}=", value)
  end
  super
  end

spec/extensions/list_spec.rb

@@ -113,6 +113,18 @@ def klass(opts={})
  "SELECT * FROM items WHERE (id = 3) ORDER BY scope_id, position LIMIT 1"]
  end
 
+ it "should have position field set to configured top value when creating first item in the list if not already set" do
+ @tc.dataset = @tc.dataset.with_autoid(1).with_fetch([[{:pos=>nil}], [{:id=>1, :position=>0}], [{:pos=>0}], [{:id=>2, :position=>1}]])
+ @tc.create.values.must_equal(:id=>1, :position=>0)
+ @tc.create.values.must_equal(:id=>2, :position=>1)
+ @db.sqls.must_equal ["SELECT max(position) AS max FROM items LIMIT 1",
+ "INSERT INTO items (position) VALUES (0)",
+ "SELECT * FROM items WHERE (id = 1) ORDER BY position LIMIT 1",
+ "SELECT max(position) AS max FROM items LIMIT 1",
+ "INSERT INTO items (position) VALUES (1)",
+ "SELECT * FROM items WHERE (id = 2) ORDER BY position LIMIT 1"]
+ end
+
  it "should update positions automatically on deletion" do
  @o.destroy
  @db.sqls.must_equal ["DELETE FROM items WHERE (id = 7)", "UPDATE items SET position = (position - 1) WHERE (position > 3)"]