Pass the result of one plugin on to the next

This fixes an issue where only the result of the last plugin
would be used when multiple plugins were activated.
This also adds a test that catches this issue.

exdir/core/dataset.py

@@ -77,13 +77,13 @@ def __getitem__(self, args):
             meta = self.meta.to_dict()
             atts = self.attrs.to_dict()
 
+            dataset_data = exdir.plugin_interface.DatasetData(data=values,
+                                                              attrs=self.attrs.to_dict(),
+                                                              meta=meta)
             for plugin in plugins:
-                dataset_data = exdir.plugin_interface.DatasetData(data=values,
-                                                                  attrs=self.attrs.to_dict(),
-                                                                  meta=meta)
-
                 dataset_data = plugin.prepare_read(dataset_data)
-                data = dataset_data.data
+
+            data = dataset_data.data
 
         return data
 

tests/test_plugins.py

@@ -211,3 +211,29 @@ def prepare_write(self, attribute_data):
     assert d.attrs["value"] == 84
     f.close()
 
+def test_reading_in_order(setup_teardown_folder):
+    class DatasetPlugin1(exdir.plugin_interface.Dataset):
+        def prepare_read(self, dataset_data):
+            dataset_data.data = dataset_data.data * 2
+            return dataset_data
+
+    class DatasetPlugin2(exdir.plugin_interface.Dataset):
+        def prepare_read(self, dataset_data):
+            dataset_data.data = dataset_data.data * 3
+            return dataset_data
+
+    plugin1 = exdir.plugin_interface.Plugin(
+        "plugin1",
+        dataset_plugins=[DatasetPlugin1()]
+    )
+    plugin2 = exdir.plugin_interface.Plugin(
+        "plugin2",
+        dataset_plugins=[DatasetPlugin2()]
+    )
+
+    f = exdir.File(setup_teardown_folder[1], "w", plugins=[plugin1, plugin2])
+    assert f
+    d = f.create_dataset("foo", data=np.array([1, 2, 3]))
+    assert all(d.data == np.array([6, 12, 18]))
+    f.close()
+