Adding customization options for export columns

This is based on what is done by
`get_details_columns`/`column_details_list`/`column_details_exclude_list`
with the added complication that `get_export_columns` also checks
`column_list` before attempting to invoke `scaffold_list_columns`.

flask_admin/model/base.py

@@ -168,6 +168,17 @@ class BaseModelView(BaseView, ActionsMixin):
         Collection of fields excluded from the details view.
     """
 
+    column_export_list = None
+    """
+        Collection of the field names included in the export.
+        If set to `None`, will get them from the model.
+    """
+
+    column_export_exclude_list = None
+    """
+        Collection of fields excluded from the export.
+    """
+
     column_formatters = ObsoleteAttr('column_formatters', 'list_formatters', dict())
     """
         Dictionary of list view column formatters.
@@ -748,6 +759,10 @@ class BaseModelView(BaseView, ActionsMixin):
         if self.can_view_details:
             self._details_columns = self.get_details_columns()
 
+        # Export view
+        if self.can_export:
+            self._export_columns = self.get_export_columns()
+
         # Labels
         if self.column_labels is None:
             self.column_labels = {}
@@ -858,6 +873,28 @@ class BaseModelView(BaseView, ActionsMixin):
 
         return [(c, self.get_column_name(c)) for c in columns]
 
+    def get_export_columns(self):
+        """
+            Returns a list of the model field names in the export view. If
+            `column_export_list` was set, returns it. Otherwise, if
+            `column_list` was set, returns it. Otherwise calls
+            `scaffold_list_columns` to generate the list from the model.
+        """
+        columns = self.column_export_list
+
+        if columns is None:
+            columns = self.column_list
+
+            if columns is None:
+                columns = self.scaffold_list_columns()
+
+            # Filter excluded columns
+            if self.column_export_exclude_list:
+                columns = [c for c in columns
+                           if c not in self.column_export_exclude_list]
+
+        return [(c, self.get_column_name(c)) for c in columns]
+
     def scaffold_sortable_columns(self):
         """
             Returns dictionary of sortable columns. Must be implemented in
@@ -1963,12 +2000,12 @@ class BaseModelView(BaseView, ActionsMixin):
 
         def generate():
             # Append the column titles at the beginning
-            titles = [csv_encode(c[1]) for c in self._list_columns]
+            titles = [csv_encode(c[1]) for c in self._export_columns]
             yield writer.writerow(titles)
 
             for row in data:
                 vals = [csv_encode(self.get_export_value(row, c[0]))
-                        for c in self._list_columns]
+                        for c in self._export_columns]
                 yield writer.writerow(vals)
 
         filename = '%s_%s.csv' % (self.name,

flask_admin/tests/test_model.py

@@ -579,6 +579,36 @@ def test_export_csv():
         "col1_2,col2_2\r\n"
         "col1_3,col2_3\r\n" == data)
 
+    # test explicit use of column_export_list
+    view = MockModelView(Model, view_data, can_export=True,
+                         column_list=['col1', 'col2'],
+                         column_export_list=['id','col1','col2'])
+    admin.add_view(view)
+
+    rv = client.get('/admin/model/export/csv/')
+    data = rv.data.decode('utf-8')
+    eq_(rv.mimetype, 'text/csv')
+    eq_(rv.status_code, 200)
+    ok_("Id,Col1,Col2\r\n"
+        "1,col1_1,col2_1\r\n"
+        "2,col1_2,col2_2\r\n"
+        "3,col1_3,col2_3\r\n" == data)
+
+    # test explicit use of column_export_exclude_list
+    view = MockModelView(Model, view_data, can_export=True,
+                         column_list=['col1', 'col2'],
+                         column_export_exclude_list=['col2'])
+    admin.add_view(view)
+
+    rv = client.get('/admin/model/export/csv/')
+    data = rv.data.decode('utf-8')
+    eq_(rv.mimetype, 'text/csv')
+    eq_(rv.status_code, 200)
+    ok_("Col1\r\n"
+        "col1_1\r\n"
+        "col1_2\r\n"
+        "col1_3\r\n" == data)
+
     # test utf8 characters in csv export
     view_data[4] = Model(1, u'\u2013ut8_1\u2013', u'\u2013utf8_2\u2013')
     view = MockModelView(Model, view_data, can_export=True,