Merge pull request #138 from fabiansinz/master

Limit and offset in fetch object

Author: dimitri-yatsenko

datajoint/fetch.py

@@ -2,6 +2,7 @@
 from functools import wraps
 import itertools
 import re
+import warnings
 from .blob import unpack
 import numpy as np
 from datajoint import DataJointError
@@ -41,17 +42,11 @@ def __init__(self, relation):
             self._relation = relation._relation
         else:
             self.behavior = dict(
-                offset=0, limit=None, order_by=None, as_dict=False
+                offset=None, limit=None, order_by=None, as_dict=False
             )
             self._relation = relation
 
 
-    @copy_first
-    def from_to(self, fro, to):
-        self.behavior['offset'] = fro
-        self.behavior['limit'] = to - fro
-        return self
-
     @copy_first
     def order_by(self, *args):
         if len(args) > 0:
@@ -64,10 +59,18 @@ def as_dict(self):
         return self
 
     @copy_first
-    def limit_to(self, limit):
+    def limit(self, limit):
         self.behavior['limit'] = limit
         return self
 
+    @copy_first
+    def offset(self, offset):
+        if self.behavior['limit'] is None:
+            warnings.warn('You should supply a limit together with an offset,')
+        self.behavior['offset'] = offset
+        return self
+
+
     @copy_first
     def set_behavior(self, **kwargs):
         self.behavior.update(kwargs)
@@ -86,7 +89,9 @@ def __call__(self, **kwargs):
 
         """
         behavior = dict(self.behavior, **kwargs)
-
+        if behavior['limit'] is None and behavior['offset'] is not None:
+            warnings.warn('Offset set, but no limit. Setting limit to a large number. Consider setting a limit yourself.')
+            behavior['limit'] = 2*len(self._relation)
         cur = self._relation.cursor(**behavior)
 
         heading = self._relation.heading

tests/test_fetch.py

@@ -67,22 +67,22 @@ def test_order_by_direct(self):
         for c, l in zip(cur, langs):
             assert_true(np.all([cc == ll for cc, ll in zip(c, l)]), 'Sorting order is different')
 
-    def test_limit_to(self):
-        """Test the limit_to function """
+    def test_limit(self):
+        """Test the limit function """
         langs = schema.Language.contents
 
-        cur = self.lang.fetch.limit_to(4)(order_by=['language', 'name DESC'])
+        cur = self.lang.fetch.limit(4)(order_by=['language', 'name DESC'])
         langs.sort(key=itemgetter(0), reverse=True)
         langs.sort(key=itemgetter(1), reverse=False)
         assert_equal(len(cur), 4, 'Length is not correct')
         for c, l in list(zip(cur, langs))[:4]:
             assert_true(np.all([cc == ll for cc, ll in zip(c, l)]), 'Sorting order is different')
 
-    def test_from_to(self):
-        """Test the from_to function """
+    def test_limit_offset(self):
+        """Test the limit and offset functions together"""
         langs = schema.Language.contents
 
-        cur = self.lang.fetch.from_to(2, 6)(order_by=['language', 'name DESC'])
+        cur = self.lang.fetch(offset=2, limit=4, order_by=['language', 'name DESC'])
         langs.sort(key=itemgetter(0), reverse=True)
         langs.sort(key=itemgetter(1), reverse=False)
         assert_equal(len(cur), 4, 'Length is not correct')