Load data with user defined schema (#150)

* Load data with the supplied schema

* Test for upload data with different df and user schema

Author: aktech

pandas_gbq/gbq.py

@@ -562,7 +562,7 @@ def load_data(
         try:
             for remaining_rows in _load.load_chunks(
                     self.client, dataframe, dataset_id, table_id,
-                    chunksize=chunksize):
+                    chunksize=chunksize, schema=schema):
                 self._print("\rLoad is {0}% Complete".format(
                     ((total_rows - remaining_rows) * 100) / total_rows))
         except self.http_error as ex:

pandas_gbq/tests/test_gbq.py

@@ -1412,6 +1412,23 @@ def test_upload_data_with_timestamp(self):
         result = result_df['times'].sort_values()
         tm.assert_numpy_array_equal(expected.values, result.values)
 
+    def test_upload_data_with_different_df_and_user_schema(self):
+        df = tm.makeMixedDataFrame()
+        df['A'] = df['A'].astype(str)
+        df['B'] = df['B'].astype(str)
+        test_id = "22"
+        test_schema = [{'name': 'A', 'type': 'FLOAT'},
+                       {'name': 'B', 'type': 'FLOAT'},
+                       {'name': 'C', 'type': 'STRING'},
+                       {'name': 'D', 'type': 'TIMESTAMP'}]
+        destination_table = self.destination_table + test_id
+        gbq.to_gbq(df, destination_table, _get_project_id(),
+                   private_key=self.credentials,
+                   table_schema=test_schema)
+        dataset, table = destination_table.split('.')
+        assert self.table.verify_schema(dataset, table,
+                                        dict(fields=test_schema))
+
     def test_list_dataset(self):
         dataset_id = self.dataset_prefix + "1"
         assert dataset_id in self.dataset.datasets()