从DynamoDb查询的Python脚本未提供所有项目 [英] Python Script to query from DynamoDb not giving all items

问题描述

我已经编写了以下python代码以从表中获取数据，但未按我的要求获取所有项目。当我检查DynamoDb的AWS控制台页面时，与从脚本中获取的内容相比，我看到的条目更多。

I have written following python code to fetch data from a table but its not fetching all the items as I want. When I check on AWS console page of DynamoDb, I can see much more entries as compared to what I get from script.

from __future__ import print_function # Python 2/3 compatibility
import boto3
import json
import decimal
from datetime import datetime
from boto3.dynamodb.conditions import Key, Attr
import sys

# Helper class to convert a DynamoDB item to JSON.
class DecimalEncoder(json.JSONEncoder):
    def default(self, o):
        if isinstance(o, decimal.Decimal):
            if o % 1 > 0:
                return float(o)
            else:
                return int(o)
        return super(DecimalEncoder, self).default(o)

dynamodb = boto3.resource('dynamodb', aws_access_key_id = '',
        aws_secret_access_key = '',
        region_name='eu-west-1', endpoint_url="http://dynamodb.eu-west-1.amazonaws.com")

mplaceId = int(sys.argv[1])
table = dynamodb.Table('XYZ')

response = table.query(
    KeyConditionExpression=Key('mplaceId').eq(mplaceId)
)

print('Number of entries found ', len(response['Items']))

我也从aws控制台执行了同样的操作。通过mplaceId查询。

I did the same thing from aws console also. Query by mplaceId.

发生这种情况的任何原因吗？

Any reason why its happening?

推荐答案

dynamodb.Table.query（）返回最大1MB的数据。从 boto3 文档：

dynamodb.Table.query() returns at max 1MB of data. From the boto3 documentation:

单个 Query 操作将读取最多设置的最大项目数（如果使用 Limit 参数）或最多1 MB的数据，然后使用<$对结果进行任何过滤c $ c> FilterExpression 。如果响应中存在 LastEvaluatedKey ，则需要对结果集进行分页。有关更多信息，请参见对结果进行分页在Amazon DynamoDB开发人员指南中。

A single Query operation will read up to the maximum number of items set (if using the Limit parameter) or a maximum of 1 MB of data and then apply any filtering to the results using FilterExpression. If LastEvaluatedKey is present in the response, you will need to paginate the result set. For more information, see Paginating the Results in the Amazon DynamoDB Developer Guide .

实际上并没有 boto3 的限制，但对基础查询 -API有所限制。

That's actually no boto3-limitation, but a limitation of the underlying query-API.

除了自己实施分页功能外，您还可以使用 boto3 的内置分页。这是一个显示 paginator的示例用于查询 boto3 提供的DynamoDB表：

Instead of implementing pagination yourself, you can use boto3's built-in pagination . Here is an example showing the use of the paginator for querying DynamoDB tables provided by boto3:

dynamodb_client = boto3.client('dynamodb')
paginator = dynamodb_client.get_paginator('query')
page_iterator = paginator.paginate(KeyConditionExpression=Key('mplaceId').eq(mplaceId))

for page in page_iterator:
    print(page['Items'])

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