DynamoDB:UpdateItem，忽略 ExpressionAttributeValues 中的 Null 值 [英] DynamoDB: UpdateItem, Ignore Null values in ExpressionAttributeValues

问题描述

我正在使用 DynamoDB UpdateItem 更新记录我的数据库.像这样的基本功能对我有用.

I'm using DynamoDB UpdateItem to update records in my DB. A basic function like this is working for me.

var user = {
    userID: '123213',
    name: 'John Doe',
    age: 12,
    type: 'creator'
};
var params = {
    TableName:table,
    Key:{
        "UserID": user.userID
    },
    UpdateExpression: "set Name = :r, Age=:p, Type=:a",
    ExpressionAttributeValues:{
        ":r":user.name,
        ":p":user.age,
        ":a":user.type
    },
    ReturnValues:"UPDATED_NEW"
};

docClient.update(params, function(err, data) {
    if (err) {
        console.error("Unable to update item. Error JSON:", JSON.stringify(err, null, 2));
    } else {
        console.log("UpdateItem succeeded:", JSON.stringify(data, null, 2));
    }
});

但是...

如果我只想更新一个属性，名称，如下所示:

If I'd like to only update one attribute, the name, like this:

 var user = {
        userID: '123213',
        name: 'John Smith'
    };
var params = {
    TableName:table,
    Key:{
        "UserID": user.userID
    },
    UpdateExpression: "set Name = :r, Age=:p, Type=:a",
    ExpressionAttributeValues:{
        ":r":user.name,
        ":p":user.age,
        ":a":user.type
    },
    ReturnValues:"UPDATED_NEW"
};

它给了我一个错误

ExpressionAttributeValues 不能为 NULL.

我知道我可以通过检查用户中的值来动态生成 UpdateExpression 字符串，如下所示:

I know that I could dynamically produce the UpdateExpression String by checking for values in user, like this:

for (var key in user) {
  if (user.hasOwnProperty(key)) {
    ...add to DynamicUpdateExpression..
  }
}

但是有没有办法让 updateItem 忽略空值而只更新 name?

but is there a way that I can tell updateItem to ignore the null values and only update the name?

推荐答案

我也在问同样的问题...在 Java 中有 SaveBehavior.UPDATE_SKIP_NULL_ATTRIBUTES 但我在 aws-sdk for nodejs 中找不到类似的东西.

I was asking the same question...In Java there's the SaveBehavior.UPDATE_SKIP_NULL_ATTRIBUTES but I couldn't find anything like that in aws-sdk for nodejs.

您可以使用 AttributeUpdates 而不是 UpdateExpression 来做出更简洁的解决方法:

You could use AttributeUpdates instead of UpdateExpression to make a cleaner workaround:

const AWS      = require(aws-sdk);
const bluebird = require('bluebird');
const _        = require('lodash');

AWS.config.setPromisesDependency(bluebird);

const dynamodb = new AWS.DynamoDB.DocumentClient();

var skipNullAttributes = (attributes) => {
  return _.omitBy(attributes, (attr) => { 
    return _.isNil(attr.Value); 
  }); 
}

var update = (id, attributes) => {
  var params = {
    TableName       : 'MyTableName',
    Key             : { id: id },
    AttributeUpdates: skipNullAttributes(attributes)
  };

  return dynamodb.update(params).promise();
}

exports.handler = (event, context, callback) => {
  var body   = JSON.parse(event.body);
  var userId = event.pathParameters.id;

  var attributes = {
    firstName: { Action: 'PUT', Value: body.firstName },
    lastName : { Action: 'PUT', Value: body.lastName  }
  };

  update(userId, attributes)
    .then((result) => console.log(result) )
    .catch((error) => console.error(error) );

  callback(null, {statusCode: 200, body: JSON.stringify({message: 'done!'})});
}

这篇关于DynamoDB:UpdateItem，忽略 ExpressionAttributeValues 中的 Null 值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！