AWS DynamoDB 尝试添加到集合 - 操作数不正确

问题描述

我正在创建一个使用 Nodejs 和 DynamoDB 作为后端的 API.我正在尝试更新一个项目以添加到一组朋友"中.当我更新用户时，我收到错误消息无效的 UpdateExpression:运算符或函数的操作数类型不正确；运算符:ADD，操作数类型:MAP".我的理解是，当添加到不存在的集合时，将创建该集合.如果它已经存在，则应将新值添加到集合中.我不明白为什么我尝试添加的集合被读取为地图.

I am creating an API using Nodejs and DynamoDB as a back end. I am attempting to update an item to add to a set of "friends". When I update the user, I get the error, "Invalid UpdateExpression: Incorrect operand type for operator or function; operator: ADD, operand type: MAP". My understanding is that when adding to a set that does not exist, the set will be created. If it already exists, the new value should be added to the set. I do not understand why the set I attempt to ADD is being read as a map.

如何创建用户:

var params = {
    TableName: "users",
    Item:{
        "id": Number(id),
        "name": name,
        "password": password
    }
};

documentClient.put(params, function(err, data) {
    if(err)
        res.json(500, err);
    else
        res.json(200, data);
});

如何添加朋友:

var params = {
    TableName: "users",
    Key: {
        "id": id
    },
    UpdateExpression: "ADD friends :friendId",
    ExpressionAttributeValues: {
        ":friendId": { "NS": [friendId] }
    },
    ReturnValues: "UPDATED_NEW"
};

documentClient.update(params, function(err, data) {
    if(err)
        res.json(500, err);
    else
        res.json(200, data);
});

推荐答案

这个问题在这里有答案

https://stackoverflow.com/a/38960676/4975772

这是根据您的问题格式化的相关代码

Here's the relevant code formatted to fit your question

let AWS = require('aws-sdk');
let docClient = new AWS.DynamoDB.DocumentClient();

...

var params = {
    TableName : 'users',
    Key: {'id': id},
    UpdateExpression : 'ADD #friends :friendId',
    ExpressionAttributeNames : {
      '#friends' : 'friends'
    },
    ExpressionAttributeValues : {
      ':friendId' : docClient.createSet([friendId])
    },
    ReturnValues: 'UPDATED_NEW'
};

docClient.update(params, callback);

如果该集合不存在，那么该代码将为您创建它.您还可以使用不同的集合运行该代码以更新集合的元素.超级方便.

If the set doesn't exist, then that code will create it for you. You can also run that code with a different set to update the set's elements. Super convenient.

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