adding in paginate method for proper limit and offset calculation

spec/model/model_spec.cr

@@ -328,5 +328,36 @@ module ModelSpec
         end
       end
     end
+
+    context "with pagination" do
+      it "can pull the next 5 users from page 2" do
+        temporary do
+          reinit
+
+          15.times do |x|
+            User.create!({first_name: "user#{x}"})
+          end
+
+          users = User.query.paginate(page: 2, per_page: 5)
+          users.map(&.first_name).should eq ["user5", "user6", "user7", "user8", "user9"]
+          users.total_entries.should eq 15
+        end
+      end
+
+      it "can paginate with where clause" do
+        temporary do
+          reinit
+          last_names = ["smith", "jones"]
+          15.times do |x|
+            last_name = last_names[x % 2]?
+            User.create!({first_name: "user#{x}", last_name: last_name})
+          end
+
+          users = User.query.where { last_name == "smith" }.paginate(page: 1, per_page: 5)
+          users.map(&.first_name).should eq ["user0", "user2", "user4", "user6", "user8"]
+          users.total_entries.should eq 8
+        end
+      end
+    end
   end
 end

src/clear/sql/query/with_pagination.cr

@@ -1,9 +1,26 @@
 module Clear::SQL::Query::WithPagination
+  DEFAULT_LIMIT = 50
+  DEFAULT_PAGE = 1
 
   macro included
     property total_entries : Int64? = nil  
   end
 
+  # Maybe this goes on the Collection?
+  def paginate(page : Int32 = DEFAULT_PAGE, per_page : Int32 = DEFAULT_LIMIT)
+    # Need to clear these values to get total count first
+    clear_limit.clear_offset
+    # TODO: this fails. Maybe something with clear_select? 
+    # @total_entries = count
+    @total_entries = Clear::SQL.connection.scalar("SELECT COUNT(*) #{print_froms} #{print_wheres}").as(Int64)
+
+    # Calculate proper offset and set limit
+    page = page < 1 ? 1 : page
+    @limit = per_page.to_i64
+    @offset = (per_page * (page - 1)).to_i64
+    change!
+  end
+
   def per_page
     limit
   end