Python中作为json数组的扳手SELECT语句

我试图在扳手中运行select语句，该语句返回多行并将结果转换为json格式

代码如下：

def fetchmessages(self, pushid):
            rc = ResultCode.SUCCESS
            messages = ""

            def selectmessages(transaction):
                    messages = transaction.execute_update(
                    "SELECT Message.message_text FROM Message LEFT JOIN MessageStatus "
                    "ON (Message.message_id = MessageStatus.message_id) WHERE "
                    "MessageStatus.push_id = @id",
                    params={'id' : (pushid)},
                    param_types={'id' : param_types.STRING}
            )

            try:
                    self.client.run_in_transaction(selectmessages)
            except Exception as fetchexception:
                    rc = ResultCode.ERR_NO_MSG_FOUND
                    self.logger.debug(fetchexception)
                    pass

            if ResultCode.SUCCESS:
                    output = "{ 'pushid':'" + pushid + "', 'messages':" + messages + ", 'resultcode':" + str(rc.value) + "}"

            return output

调用函数只是通过jsonify运行输出并将其打印出来。上面的代码打印出来：

"{ 'pushid':'cdd92f4ce847efa5c7f', 'messages':, 'resultcode':1}"

我希望它打印出如下内容：

"{ 'pushid':'cdd92f4ce847efa5c7f', 'Messages': [{'message': 'foo bar'}, { 'message': 'core dump'}], 'resultcode': 1}"

---

我该怎么做呢？

看起来您的事务只是一个select语句。我建议使用如下所示的execute_sql方法：

spanner_client = spanner.Client()
instance = spanner_client.instance(instance_id)
database = instance.database(database_id)

with database.snapshot() as snapshot:
    results = snapshot.execute_sql(
        "SELECT Message.message_text FROM Message LEFT JOIN MessageStatus "
        "ON (Message.message_id = MessageStatus.message_id) WHERE "
        "MessageStatus.push_id = @id",
        params={'id' : (pushid)},
        param_types={'id' : param_types.STRING})

    for row in results:
        print(u'Message: {}'.format(*row))

您的

JOIN

声明中有一个问题：

• 每个

  push\u id

  包含几个

  message\u id

  ，因此这两个表应该在

  push\u id

  上连接，而不是

  message\u id

表

消息

和

消息状态

之间的潜在关系问题：

• push_id

  应该是

  MessageStatus

  的主键，而

  MessageStatus

  应该是

  Message

  的父项，请使用以下示例检查DDL设置是否正确：

DDL：

查询脚本：

from google.cloud import spanner

def fetch_messages(instance_id, database_id):
    spanner_client = spanner.Client()
    instance = spanner_client.instance(instance_id)
    database = instance.database(database_id)

    with database.snapshot() as snapshot:
        results = snapshot.execute_sql(
            'SELECT Message.push_id, Message.message_id, Message.message_text FROM Message LEFT JOIN MessageStatus '
            'ON MessageStatus.push_id = Message.push_id WHERE MessageStatus.push_id="JDHK65FTRD832KJ"')
        for row in results:
            print(u'push_id: {}, message_id: {}, message_text: {}'.format(*row))


fetch_messages([INSTANCE_ID], [DATABASE_ID])

结果:

push_id: JDHK65FTRD832KJ, message_id: 1, message_text: First
push_id: JDHK65FTRD832KJ, message_id: 2, message_text: Second
push_id: JDHK65FTRD832KJ, message_id: 3, message_text: Third

GCP资源：

push_id: JDHK65FTRD832KJ, message_id: 1, message_text: First
push_id: JDHK65FTRD832KJ, message_id: 2, message_text: Second
push_id: JDHK65FTRD832KJ, message_id: 3, message_text: Third