Make dataset.limit(nil, nil) reset offset as well as limit (Fixes #571)

Note that you should probably use unlimited instead of limit(nil,nil).

CHANGELOG

@@ -1,5 +1,7 @@
 === HEAD
 
+* Make dataset.limit(nil, nil) reset offset as well as limit (jeremyevans) (#571)
+
 * Support IMMEDIATE/EXCLUSIVE/DEFERRED transaction modes on SQLite (Eric Wong)
 
 * Major change in the Database <-> ConnectionPool interface (jeremyevans)

lib/sequel/dataset/query.rb

@@ -592,7 +592,7 @@ def join_table(type, table, expr=nil, options={}, &block)
     #   DB[:items].limit(10...20) # SELECT * FROM items LIMIT 10 OFFSET 10
     #   DB[:items].limit(10..20) # SELECT * FROM items LIMIT 11 OFFSET 10
     #   DB[:items].limit(nil, 20) # SELECT * FROM items OFFSET 20
-    def limit(l, o = nil)
+    def limit(l, o = (no_offset = true; nil))
       return from_self.limit(l, o) if @opts[:sql]
 
       if Range === l
@@ -610,6 +610,8 @@ def limit(l, o = nil)
           raise(Error, 'Offsets must be greater than or equal to 0') unless o >= 0
         end
         opts[:offset] = o
+      elsif !no_offset
+        opts[:offset] = nil
       end
       clone(opts)
     end

spec/core/dataset_spec.rb

@@ -1620,6 +1620,12 @@ def d.to_s; "adsf" end
     @dataset.limit(6, Sequel.function(:a) - 1).sql.should == 'SELECT * FROM test LIMIT 6 OFFSET (a() - 1)'
   end
 
+  specify "should be able to reset limit and offset with nil values" do
+    @dataset.limit(6).limit(nil).sql.should == 'SELECT * FROM test'
+    @dataset.limit(6, 1).limit(nil).sql.should == 'SELECT * FROM test OFFSET 1'
+    @dataset.limit(6, 1).limit(nil, nil).sql.should == 'SELECT * FROM test'
+  end
+
   specify "should work with fixed sql datasets" do
     @dataset.opts[:sql] = 'select * from cccc'
     @dataset.limit(6, 10).sql.should == 'SELECT * FROM (select * from cccc) AS t1 LIMIT 6 OFFSET 10'