[FIX] web: KanbanModel: don't allow nested groups

Nested groups is only for list views. In kanban, only the first
grouping level is taken into account.

addons/web/static/src/js/views/kanban/kanban_model.js

@@ -167,6 +167,25 @@ var KanbanModel = BasicModel.extend({
             return parentID;
         });
     },
+
+    //--------------------------------------------------------------------------
+    // Private
+    //--------------------------------------------------------------------------
+
+    /**
+     * Ensures that there is no nested groups in Kanban (only the first grouping
+     * level is taken into account).
+     *
+     * @override
+     * @private
+     * @param {Object} list valid resource object
+     */
+    _readGroup: function (list) {
+        if (list.groupedBy.length > 1) {
+            list.groupedBy = [list.groupedBy[0]];
+        }
+        return this._super.apply(this, arguments);
+    },
 });
 
 return KanbanModel;

addons/web/static/test/views/kanban_model_tests.js

@@ -155,6 +155,36 @@ QUnit.module('Views', {
         });
     });
 
+    QUnit.test('kanban model does not allow nested groups', function (assert) {
+        assert.expect(2);
+
+        var model = createModel({
+            Model: KanbanModel,
+            data: this.data,
+            mockRPC: function (route, args) {
+                if (args.method === 'read_group') {
+                    assert.deepEqual(args.kwargs.groupby, ['product_id'],
+                        "the second level of groupBy should have been removed");
+                }
+                return this._super.apply(this, arguments);
+            },
+        });
+
+        var params = _.extend(this.params, {
+            groupedBy: ['product_id', 'qux'],
+            fieldNames: ['foo'],
+        });
+
+        model.load(params).then(function (resultID) {
+            var state = model.get(resultID);
+
+            assert.deepEqual(state.groupedBy, ['product_id'],
+                "the second level of groupBy should have been removed");
+
+            model.destroy();
+        });
+    });
+
 });
 
 });