[#1725] Datastore must be the first IDatastore plugin loaded

This allows extensions to rely on it running before them.

ckanext/datastore/plugin.py

@@ -39,6 +39,18 @@ class DatastorePlugin(p.SingletonPlugin):
     legacy_mode = False
     resource_show_action = None
 
+    def __init__(self, *args, **kwargs):
+        idatastore_extensions = p.PluginImplementations(interfaces.IDatastore)
+        idatastore_extensions = idatastore_extensions.extensions()
+
+        if idatastore_extensions and idatastore_extensions[0] != self:
+            msg = ('The "datastore" extension must be the first IDatastore '
+                   'extension loaded. Change the order it is loaded in '
+                   '"ckan.plugins" in your CKAN .ini file and try again.')
+            raise DatastoreException(msg)
+
+        super(self.__class__, self).__init__(*args, **kwargs)
+
     def configure(self, config):
         self.config = config
         # check for ckan.datastore.write_url and ckan.datastore.read_url

ckanext/datastore/tests/test_plugin.py

@@ -0,0 +1,27 @@
+import nose
+
+import ckan.plugins as p
+import ckanext.datastore.plugin as datastore
+
+
+assert_raises = nose.tools.assert_raises
+
+
+class TestPlugin(object):
+    @classmethod
+    def setup(cls):
+        if p.plugin_loaded('datastore'):
+            p.unload('datastore')
+        if p.plugin_loaded('sample_datastore_plugin'):
+            p.unload('sample_datastore_plugin')
+
+    def test_loading_datastore_first_works(self):
+        p.load('datastore')
+        p.load('sample_datastore_plugin')
+        p.unload('sample_datastore_plugin')
+        p.unload('datastore')
+
+    def test_loading_datastore_last_doesnt_work(self):
+        p.load('sample_datastore_plugin')
+        assert_raises(datastore.DatastoreException, p.load, 'datastore')
+        p.unload('sample_datastore_plugin')