更新 dynamodb 记录中的属性

Question

我正在尝试更新我的 dynamodb table 中的现有记录。如下所示，我的 table

中有一个项目

let params = {
   TableName: proces.env.dynamoDbTable,
   Item: {
      productId: "id",
      att1: val1,
      att2: val2
      }
 }

我想执行更新。我正在使用 aws dynamodb sdk 的更新方法并将其传递给如下参数

let aws = require('aws-sdk');
 let dbb = new aws.DynamoDb.DocumentClient();
 let params = {
  TableName: process.env.tableName,
  Key: {productID}
  ExpressionAttributeNames: { "#updatedAt" : "updatedAt" }
  ExpressionAttributeValues: {":u":moment().unix(), ":val1" : a, ":val2": b}
  UpdateExpression: "SET att1 = :val1, att2: val2, #updatedAt: :u"
 }
// a, b are passed as argument to function and are optional
dbb.update(params).promise()

当参数丢失时，dynamo 引发 ExpressionAttributeValue 丢失异常，我知道它是直接的。有没有一种方法可以使用提供的属性更新我的项目

Answer 1

不幸的是，dynamodb 并没有让这变得容易。但是你可以使用一些花哨的 js 来动态创建 params 对象：

  // for some object `attrs` we find which keys we need to update
  const keys = Object.keys(attrs);
  const values = Object.values(attrs);

  // get a list of key names and value names to match the dynamodb syntax
  const attributeKeyNames = keys.map((k) => '#key_' + k);
  const attributeValueNames = keys.map((k) => ':val_' + k);

  // create individual expressions for each attribute that needs to be updated
  const expressions = attributeValueNames.map((attr, i) => {
    return `${attributeKeyNames[i]} = ${attr}`;
  });

  // add the SET keyword to the beginning of the string
  // and join all the expressions with a comma
  const UpdateExpression = 'SET ' + expressions.join(', ');

  // I use `zipObject()` from lodash https://lodash.com/docs/4.17.15#zipObject
  // it makes an object map from two arrays where the first is the keys and
  // the second is the values
  const ExpressionAttributeValues = _.zipObject(attributeValueNames, values);
  const ExpressionAttributeNames = _.zipObject(attributeKeyNames, keys);

  // now you have all the params
  const params = {
    TableName,
    Key: {
      uuid,
    },
    UpdateExpression,
    ExpressionAttributeValues,
    ExpressionAttributeNames,
  };

Answer 2

效果很好。不过要记住几件事：

如果您将带有唯一键的对象发送到更新函数中，则必须在映射表达式数组之前删除该键，否则它将包含在查询中并会出现错误：

const newObject = {...originalObject}
delete newObject.unique_key

如果你不能或不想使用 Lodash，你可以使用 Object.assign 来映射你的 keys/values 数组：

const ExpressionAttributeValues = Object.assign(...attributeValueNames.map((k, i) => ({[k]: values[i]})));
const ExpressionAttributeNames = Object.assign(...attributeKeyNames.map((k, i) => ({[k]: keys[i]})));

更新 dynamodb 记录中的属性

update attributes in a dynamodb record

amazon-web-services

node.js

amazon-dynamodb

dynamodb-queries

amazon-dynamodb-local