Question

我一直在研究Django中的应用程序。首先，为简单起见，我一直在使用sqlite3作为数据库。

然而，一旦我转移到PostgreSQL，我遇到了一个问题：一旦我清理了一个表，主键就不会重置。

此应用是一款长时间（周）播放的游戏。因此，每次新游戏开始时，所有数据都将从数据库中清除，然后添加新的随机数据。

每次清理/重建游戏时，我希望能够从1开始使用主键“重新开始”。

代码仍然按原样运行，但整数是描述游戏中对象的一种非常自然的方式。我想让每场新游戏从1开始，而不是在最后一场比赛停止的地方开始。

如何在PostgreSQL中重置主键计数器？请记住，我不需要保存表格中的数据，因为无论如何我都要擦除它。

Answer 1

在你的app目录中试试这个：

python manage.py help sqlsequencereset

将它像这样管道传输到psql中以实际运行重置：

python manage.py sqlsequencereset myapp1 myapp2 | psql

编辑：这是我在其中一个表上输出此命令的示例：

BEGIN;
SELECT setval('"project_row_id_seq"', coalesce(max("id"), 1), max("id") IS NOT null) FROM "project_row";
COMMIT;

Answer 2

如果你执行原始sql，可以这样做：

ALTER SEQUENCE youApp_id_seq RESTART WITH 1;

文档： http://www.postgresql.org/docs/8.2/static/sql-altersequence.html

Answer 3

根据＆＃34; Van Gale＆＃34;您可以通过sqlsequencereset获取解决问题的命令。

或

您可以通过这种方式在python中执行sqlsequencereset生成的SQL查询（使用默认数据库）：

from django.core.management.color import no_style
from django.db import connection

from myapps.models import MyModel1, MyModel2


sequence_sql = connection.ops.sequence_reset_sql(no_style(), [MyModel1, MyModel2])
with connection.cursor() as cursor:
    for sql in sequence_sql:
        cursor.execute(sql)

我使用 Python3.6 ， Django 2.0 和 PostgreSQL 10 测试了此代码。

Answer 4

我将自动增量主键视为数据库记录的纯内部标识符，我不喜欢将它们暴露给用户。当然，将它们用作URL的一部分是一种常见的设计，但即使有slug或其他标识符也不合适。

Answer 5

您需要截断表格。见http://www.postgresql.org/docs/8.1/static/sql-truncate.html

Answer 6

如果您不想手动获取所需的应用程序，或者如果您拥有一系列不同的数据库，则此命令将动态收集 settings.py 的所有连接并重置顺序

要运行，请使用：python manage.py reset_sequences

import psycopg2
from django.conf import settings
from django.core.management.base import BaseCommand
from django.db import connections


def dictfetchall(cursor):
    """Return all rows from a cursor as a dict"""
    columns = [col[0] for col in cursor.description]
    return [
        dict(zip(columns, row))
        for row in cursor.fetchall()
    ]


class Command(BaseCommand):
    help = "Resets sequencing errors in Postgres which normally occur due to importing/restoring a DB"

    def handle(self, *args, **options):
        # loop over all databases in system to figure out the tables that need to be reset
        for name_to_use_for_connection, connection_settings in settings.DATABASES.items():
            db_name = connection_settings['NAME']
            host = connection_settings['HOST']
            user = connection_settings['USER']
            port = connection_settings['PORT']
            password = connection_settings['PASSWORD']

            # connect to this specific DB
            conn_str = f"host={host} port={port} user={user} password={password}"

            conn = psycopg2.connect(conn_str)
            conn.autocommit = True

            select_all_table_statement = f"""SELECT *
                                    FROM information_schema.tables
                                    WHERE table_schema = 'public'
                                    ORDER BY table_name;
                                """
            # just a visual representation of where we are
            print('-' * 20, db_name)
            try:
                not_reset_tables = list()
                # use the specific name for the DB
                with connections[name_to_use_for_connection].cursor() as cursor:
                    # using the current db as the cursor connection
                    cursor.execute(select_all_table_statement)
                    rows = dictfetchall(cursor)
                    # will loop over table names in the connected DB
                    for row in rows:
                        find_pk_statement = f"""
                            SELECT k.COLUMN_NAME
                            FROM information_schema.table_constraints t
                            LEFT JOIN information_schema.key_column_usage k
                            USING(constraint_name,table_schema,table_name)
                            WHERE t.constraint_type='PRIMARY KEY'
                                AND t.table_name='{row['table_name']}';
                        """
                        cursor.execute(find_pk_statement)
                        pk_column_names = dictfetchall(cursor)
                        for pk_dict in pk_column_names:
                            column_name = pk_dict['column_name']

                        # time to build the reset sequence command for each table
                        # taken from django: https://docs.djangoproject.com/en/3.0/ref/django-admin/#sqlsequencereset
                        # example: SELECT setval(pg_get_serial_sequence('"[TABLE]"','id'), coalesce(max("id"), 1), max("id") IS NOT null) FROM "[TABLE]";
                        try:
                            reset_statement = f"""SELECT setval(pg_get_serial_sequence('"{row['table_name']}"','{column_name}'), 
                                                    coalesce(max("{column_name}"), 1), max("{column_name}") IS NOT null) FROM "{row['table_name']}" """
                            cursor.execute(reset_statement)
                            return_values = dictfetchall(cursor)
                            # will be 1 row
                            for value in return_values:
                                print(f"Sequence reset to {value['setval']} for {row['table_name']}")
                        except Exception as ex:
                            # will only fail if PK is not an integer...
                            # currently in my system this is from django.contrib.sessions
                            not_reset_tables.append(f"{row['table_name']} not reset")

            except psycopg2.Error as ex:
                raise SystemExit(f'Error: {ex}')

            conn.close()
            print('-' * 5, ' ALL ERRORS ', '-' * 5)
            for item_statement in not_reset_tables:
                # shows which tables produced errors, so far I have only
                # seen this with PK's that are not integers because of the MAX() method
                print(item_statement)

            # just a visual representation of where we are
            print('-' * 20, db_name)

Django + PostgreSQL：如何重置主键？

6 个答案: