仅更新给定的值并忽略 dynamodb 中的其他值

Question

您好，我正在编写一个 lambda 函数，它将使用 boto3 更新 DynamoDb。在此代码中，employee_id 是自动生成的，但您必须提供 last_name 或 first_name。我用 if-else 来做。如果属性趋于增加，则检查也会增加。我无法继续使用 if 条件。我该如何解决这个问题我应该做出哪些改变

import boto3
import json

dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('Employee')

def lambda_handler(event, context):

    employee_id = event['employee_id']

    if 'first_name' in event and 'last_name' not in event:

        first_name = event['first_name']
        UpdateExpression = 'SET first_name = :val1'
        ExpressionAttributeValues = {':val1': first_name }

    elif 'last_name' in event and 'first_name' not in event:

        last_name = event['last_name']
        UpdateExpression = 'SET last_name = :val1'
        ExpressionAttributeValues = {':val1': last_name}

    elif 'first_name' in event and 'last_name' in event:

        last_name = event['last_name']
        first_name= event['first_name']
        UpdateExpression = 'SET last_name = :val1, first_name = :val2'
        ExpressionAttributeValues = {
                ':val1': last_name,
                ':val2': first_name
            }

    else:
        raise ValueError("first_name and last_name not given")


    update = table.update_item(
        Key={
            'employee_id': employee_id
        },
        ConditionExpression= 'attribute_exists(employee_id)',
        UpdateExpression=UpdateExpression,
        ExpressionAttributeValues=ExpressionAttributeValues
    )

我想出但不起作用的代码

import boto3
import json
dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('Employee')

def lambda_handler(event, context):
    employee_id = event['employee_id']
    last_name= event['last_name']
    first_name= event['first_name']
    column = [first_name,last_name]
    for i in range(0,len(column):
       query = 'SET {} = :val1,:val2'.format(column[i])
       response = table.update_item(
           Key={
            'employee_id': employee_id
            },
            ConditionExpression= 'attribute_exists(employee_id)',
            UpdateExpression = query,
            ExpressionAttributeValues={
                ':val1': first_name,
                ':val2': last_name
            },
            ReturnValues="UPDATED_NEW"
        )

Answer 1

您应该考虑分别存储更新表达式和表达式值，然后将完整的集合传递给 Lambda 函数。

这还允许您针对每个参数进行验证（也许将其分解为验证函数以避免函数过大）。这样您就可以同时支持必需参数和可选参数，然后在最后验证更新表达式是否具有有效参数。

也许像下面这样？

import boto3
import json

dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('Employee')

def lambda_handler(event, context):

    update_expression_values = []
    expression_attribute_values = {}
    
    if 'employee_id' in event:
        employee_id = event['employee_id']
    else:
        raise ValueError("employee_id not given")
    
    if 'first_name' in event:
        update_expression_values.append('first_name = :val_first_name')
        expression_attribute_values[':val_first_name'] = event['first_name']

    if 'last_name' in event:

        update_expression_values.append('last_name = :val_last_name')
        expression_attribute_values[':val_last_name'] = event['last_name']

    if len(update_expression_values) < 1:
        raise ValueError("first_name and last_name not given")

    seperator = ','
    
    update = table.update_item(
        Key={
            'employee_id': employee_id
        },
        ConditionExpression= 'attribute_exists(employee_id)',
        UpdateExpression='SET ' + seperator.join(update_expression_values),
        ExpressionAttributeValues=expression_attribute_values
    )

这可以进一步分解以通过可以执行这些检查的函数重用逻辑，如下所示。

import boto3
import json

dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('Employee')

update_expression_values = []
expression_attribute_values = {}

def lambda_handler(event, context):
    global update_expression_values
    global expression_attribute_values
    
    update_expression_values = []
    expression_attribute_values = {}

    if 'employee_id' in event:
        employee_id = event['employee_id']
    else:
        raise ValueError("employee_id not given")
        
    process_event_key(event, 'first_name')
    process_event_key(event, 'last_name')
    process_event_key(event, 'new_value')

    if len(update_expression_values) < 1:
        raise ValueError("first_name and last_name not given")

    seperator = ','
    
    update = table.update_item(
        Key={
            'employee_id': employee_id
        },
        ConditionExpression= 'attribute_exists(employee_id)',
        UpdateExpression='SET ' + seperator.join(update_expression_values),
        ExpressionAttributeValues=expression_attribute_values
    )
    
def process_event_key(event, key):
    global update_expression_values
    global expression_attribute_values
    
    if key in event:
        update_expression_values.append(key + ' = :val_' + key)
        expression_attribute_values[':val_' + key] = event[key]

测试活动

{
  "new_value": "test",
  "employee_id": "value2",
  "last_name": "value3",
  "first_name": "value4"
}

仅更新给定的值并忽略 dynamodb 中的其他值

Only update the value given and ignore other values in dynamodb

python

amazon-web-services

amazon-dynamodb

boto3

aws-lambda