fix wording and add comments

Author: sonots

CHANGELOG.md

@@ -5,14 +5,14 @@ Cleanup `auth_method`:
 * [enhancement] Support `auth_method: authorized_user` (OAuth)
 * [incompatibility change] Rename `auth_method: json_key` to `auth_method: service_account` (`json_key` is kept for backward compatibility)
 * [incompatibility change] Remove deprecated `auth_method: private_key` (p12 key)
-* [incompatibility change] Change the default `auth_method` to `application_default` from `private_key`.
+* [incompatibility change] Change the default `auth_method` to `application_default` from `private_key` because `private_key` was dropped.
 
 ## 0.5.0 - 2019-08-10
 
 * [incompatibility change] Drop deprecated `time_partitioning`.`require_partition_filter`
 * [incompatibility change] Drop `prevent_duplicate_insert` which has no use-case now
-* [incompatibility change] Change default value of `auto_create_table` to `true` from `false`
-  * Modes `replace`, `replace_backup`, `append`, `delete_in_advance`, that is, except `append_direct` requires `auto_create_table: true`.
+* [incompatibility change] Modes `replace`, `replace_backup`, `append`, and `delete_in_advance` require `auto_create_table: true` now because, previously, these modes had created a target table even with `auto_create_table: false` and made users being confused. Note that `auto_create_table: true` is always required even for a partition (a table name with a partition decorator) which may not require creating a table. This is for simplicity of logics and implementations.
+* [incompatibility change] Change default value of `auto_create_table` to `true` because the above 4 modes, that is, except `append_direct` always require `auto_create_table: true` now.
 
 ## 0.4.14 - 2019-08-10
 

README.md

@@ -37,7 +37,7 @@ OAuth flow for installed applications.
 |  location                            | string      | optional   | nil                      | geographic location of dataset. See [Location](#location) |
 |  table                               | string      | required   |                          | table name, or table name with a partition decorator such as `table_name$20160929`|
 |  auto_create_dataset                 | boolean     | optional   | false                    | automatically create dataset |
-|  auto_create_table                   | boolean     | optional   | true                     | `false` is available only for `append_direct` mode. Other modes requires `true`. See [Dynamic Table Creating](#dynamic-table-creating) and [Time Partitioning](#time-partitioning) |
+|  auto_create_table                   | boolean     | optional   | true                     | `false` is available only for `append_direct` mode. Other modes require `true`. See [Dynamic Table Creating](#dynamic-table-creating) and [Time Partitioning](#time-partitioning) |
 |  schema_file                         | string      | optional   |                          | /path/to/schema.json |
 |  template_table                      | string      | optional   |                          | template table name. See [Dynamic Table Creating](#dynamic-table-creating) |
 |  job_status_max_polling_time         | int         | optional   | 3600 sec                 | Max job status polling time |
@@ -256,12 +256,12 @@ Table ids are formatted at runtime
 using the local time of the embulk server.
 
 For example, with the configuration below,
-data is inserted into tables `table_2015_04`, `table_2015_05` and so on.
+data is inserted into tables `table_20150503`, `table_20150504` and so on.
 
 ```yaml
 out:
   type: bigquery
-  table: table_%Y_%m
+  table: table_%Y%m%d
 ```
 
 ### Dynamic table creating
@@ -276,7 +276,7 @@ Please set file path of schema.json.
 out:
   type: bigquery
   auto_create_table: true
-  table: table_%Y_%m
+  table: table_%Y%m%d
   schema_file: /path/to/schema.json
 ```
 
@@ -288,7 +288,7 @@ Plugin will try to read schema from existing table and use it as schema template
 out:
   type: bigquery
   auto_create_table: true
-  table: table_%Y_%m
+  table: table_%Y%m%d
   template_table: existing_table_name
 ```
 

lib/embulk/output/bigquery.rb

@@ -304,14 +304,14 @@ def self.auto_create(task, bigquery)
           bigquery.create_table_if_not_exists(task['table'])
         when 'replace'
           bigquery.create_table_if_not_exists(task['temp_table'])
-          bigquery.create_table_if_not_exists(task['table'])
+          bigquery.create_table_if_not_exists(task['table']) # needs for when task['table'] is a partition
         when 'append'
           bigquery.create_table_if_not_exists(task['temp_table'])
-          bigquery.create_table_if_not_exists(task['table'])
+          bigquery.create_table_if_not_exists(task['table']) # needs for when task['table'] is a partition
         when 'replace_backup'
           bigquery.create_table_if_not_exists(task['temp_table'])
           bigquery.create_table_if_not_exists(task['table'])
-          bigquery.create_table_if_not_exists(task['table_old'], dataset: task['dataset_old'])
+          bigquery.create_table_if_not_exists(task['table_old'], dataset: task['dataset_old']) # needs for when a partition
         else # append_direct
           if task['auto_create_table']
             bigquery.create_table_if_not_exists(task['table'])