Rename utils.extract_key() -> extract_from_tuple()

We have functions that have similar purpose - extract key values:

- sharding_key_module.extract_from_pk()
- sharding_key_module.extract_from_index()

Patch renames utils.extract_key() to utils.extract_from_tuple() to make
function's names consistent and make code clear.

Part of #166

crud/common/sharding.lua

@@ -34,7 +34,7 @@ function sharding.tuple_get_bucket_id(tuple, space, specified_bucket_id)
         end
         sharding_index_parts = sharding_key_fieldnos.parts
     end
-    local key = utils.extract_key(tuple, sharding_index_parts)
+    local key = utils.extract_from_tuple(tuple, sharding_index_parts)
 
     return sharding.key_get_bucket_id(key)
 end

crud/common/utils.lua

@@ -140,7 +140,7 @@ function utils.unflatten(tuple, space_format)
     return object
 end
 
-function utils.extract_key(tuple, key_parts)
+function utils.extract_from_tuple(tuple, key_parts)
     local key = {}
     for i, part in ipairs(key_parts) do
         key[i] = tuple[part.fieldno]

crud/compare/comparators.lua

@@ -171,8 +171,8 @@ function comparators.gen_tuples_comparator(cmp_operator, key_parts, field_names,
         end
     else
         return function(lhs, rhs)
-            local lhs_key = utils.extract_key(lhs, updated_key_parts)
-            local rhs_key = utils.extract_key(rhs, updated_key_parts)
+            local lhs_key = utils.extract_from_tuple(lhs, updated_key_parts)
+            local rhs_key = utils.extract_from_tuple(rhs, updated_key_parts)
             return keys_comparator(lhs_key, rhs_key)
         end
     end

crud/select/executor.lua

@@ -51,7 +51,7 @@ else
     generate_value = function(after_tuple, scan_value, index_parts, tarantool_iter)
         local cmp_operator = select_comparators.get_cmp_operator(tarantool_iter)
         local scan_comparator = select_comparators.gen_tuples_comparator(cmp_operator, index_parts)
-        local after_tuple_key = utils.extract_key(after_tuple, index_parts)
+        local after_tuple_key = utils.extract_from_tuple(after_tuple, index_parts)
         if scan_comparator(after_tuple_key, scan_value) then
             return after_tuple_key
         end

crud/select/plan.lua

@@ -208,7 +208,7 @@ function select_plan.new(space, conditions, opts)
                     local key_def = keydef_lib.new(scan_index.parts)
                     scan_value = key_def:extract_key(scan_after_tuple)
                 else
-                    scan_value = utils.extract_key(scan_after_tuple, scan_index.parts)
+                    scan_value = utils.extract_from_tuple(scan_after_tuple, scan_index.parts)
                 end
             else
                 scan_value = nil

test/unit/serialization_test.lua

@@ -150,13 +150,13 @@ g.test_unflatten = function()
     })
 end
 
-g.test_extract_key = function()
+g.test_extract_from_tuple = function()
     local tuple = {1, nil, 'Marilyn', 50}
 
-    local key = utils.extract_key(tuple, {{fieldno = 1}})
+    local key = utils.extract_from_tuple(tuple, {{fieldno = 1}})
     t.assert_equals(key, {1})
 
-    local key = utils.extract_key(tuple, {
+    local key = utils.extract_from_tuple(tuple, {
         {fieldno = 3}, {fieldno = 2}, {fieldno = 1},
     })
     t.assert_equals(key, {'Marilyn', nil, 1})