Fix handling of Class.new(ModelClass){set_dataset :table} on ruby 1.8

This was broken with the implicit table name refactoring between
4.24.0 and 4.25.0.

CHANGELOG

@@ -1,5 +1,7 @@
 === HEAD
 
+* Fix handling of Class.new(ModelClass){set_dataset :table} on ruby 1.8 (jeremyevans)
+
 * Use range function constructors instead of casts for known range types in pg_range (jeremyevans) (#1066)
 
 * Make class_table_inheritance plugin work without sti_key (jeremyevans)

lib/sequel/model/base.rb

@@ -509,11 +509,13 @@ def inherited(subclass)
           subclass.instance_variable_set(iv, sup_class_value)
         end
 
-        if @dataset && self != Model
-          subclass.set_dataset(@dataset.clone, :inherited=>true) rescue nil
-        elsif (n = subclass.name) && !n.to_s.empty?
-          db
-          subclass.set_dataset(subclass.implicit_table_name) rescue nil
+        unless ivs.include?("@dataset")
+          if @dataset && self != Model
+            subclass.set_dataset(@dataset.clone, :inherited=>true) rescue nil
+          elsif (n = subclass.name) && !n.to_s.empty?
+            db
+            subclass.set_dataset(subclass.implicit_table_name) rescue nil
+          end
         end
       end
 

spec/model/base_spec.rb

@@ -91,6 +91,13 @@ class ::BootSize < ShoeSize; end
   it "should raise if no dataset is explicitly set and the class is anonymous" do
     proc {@b.dataset}.must_raise(Sequel::Error)
   end
+
+  it "should not override dataset explicitly set when subclassing" do
+    sc = Class.new(::Elephant) do
+      set_dataset :foo
+    end
+    sc.table_name.must_equal :foo
+  end
 end
 
 describe Sequel::Model, "implicit table names" do