prevent nil return when pairs iterates through empty space

Before this patch pairs returns "nil" if target space was empty.
The reason is "has next" method of Iterator class that returns
true before first get. This patch removes "has_next" call from lua
generator function.

Closes #82

Author: olegrok

CHANGELOG.md

@@ -13,10 +13,12 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 * Fixed select by part of sharding key equal. Before this patch
   selecting by equality of partially specified multipart primary index
   value was misinterpreted as a selecting by fully specified key value.
+* Fixed iteration with `pairs` through empty space returned `nil`.
 
 ### Added
 
 * `truncate` operation
+* iterator returned by `pairs` is compatible with luafun
 
 ## [0.3.0] - 2020-10-26
 

crud/select.lua

@@ -223,11 +223,11 @@ function select_module.pairs(space_name, user_conditions, opts)
     end
 
     local gen = function(_, iter)
-        if not iter:has_next() then
+        local tuple, err = iter:get()
+        if tuple == nil then
             return nil
         end
 
-        local tuple, err = iter:get()
         if err ~= nil then
             error(string.format("Failed to get next object: %s", err))
         end