如何使用 node.js 从`AWS dynamodb` 获取/扫描所有项目

How to fetch/scan all items from `AWS dynamodb` using node.js

提问by vts

How to fetch/scan all items from AWS dynamodbusing node.js. I am posting my code here.

如何AWS dynamodb使用node.js. 我在这里发布我的代码。

var docClient = new aws.DynamoDB.DocumentClient();
    var params = {
    TableName:"users",
    KeyConditionExpression:"user_status=:status",
    ExpressionAttributeValues: {
        ":status": "Y"
    }
    };

    var queryExecute = function(callback) {
        docClient.query(params,function(err,result) {
            if(err) {
                console.log(err)
                callback(err);
                } else {
                console.log(result);

                if(result.LastEvaluatedKey) {
                    params.ExclusiveStartKey = result.LastEvaluatedKey;
                    queryExecute(callback);
                    } else {
                        callback(err,items);
                    }
                }
            });
        }
        queryExecute(callback); 

This is giving me below error.

这给了我以下错误。

ValidationException: Query condition missed key schema element: `user_id`.

Here primary key is user_id. I don't want to use it with my query condition, because I need to set a value if I mentioned primary key in KeyConditionExpression. May be I am wrong. However please suggest me a good way to fetch all items from dynamodb, which is having user_status = "Y"

这里的主键是 user_id。我不想在我的查询条件中使用它，因为如果我在KeyConditionExpression. 可能是我错了。但是，请建议我一种从 中获取所有项目的好方法dynamodb，它具有user_status = "Y"

回答by notionquest

If you would like to get the data from DynamoDB without using Hash key value, you need to use Scan API.

如果您想在不使用哈希键值的情况下从 DynamoDB 获取数据，则需要使用Scan API.

Note:The Scan API reads all the items in the table to get the results. So, it is a costly operation in DynamoDB.

注意：Scan API 读取表中的所有项目以获取结果。因此，在 DynamoDB 中这是一项代价高昂的操作。

Alternate Approach :Use GSI

替代方法：使用 GSI

Scan Code for the above sceanario:-

上述场景的扫描码：-

var docClient = new AWS.DynamoDB.DocumentClient();

var params = {
    TableName: "users",
    FilterExpression: "#user_status = :user_status_val",
    ExpressionAttributeNames: {
        "#user_status": "user_status",
    },
    ExpressionAttributeValues: { ":user_status_val": 'somestatus' }

};

docClient.scan(params, onScan);
var count = 0;

function onScan(err, data) {
    if (err) {
        console.error("Unable to scan the table. Error JSON:", JSON.stringify(err, null, 2));
    } else {        
        console.log("Scan succeeded.");
        data.Items.forEach(function(itemdata) {
           console.log("Item :", ++count,JSON.stringify(itemdata));
        });

        // continue scanning if we have more items
        if (typeof data.LastEvaluatedKey != "undefined") {
            console.log("Scanning for more...");
            params.ExclusiveStartKey = data.LastEvaluatedKey;
            docClient.scan(params, onScan);
        }
    }
}

回答by Hank

This is working for me:

这对我有用：

export const scanTable = async (tableName) => {
    const params = {
        TableName: tableName,
    };

    let scanResults = [];
    let items;
    do{
        items =  await documentClient.scan(params).promise();
        items.Items.forEach((item) => scanResults.push(item));
        params.ExclusiveStartKey  = items.LastEvaluatedKey;
    }while(typeof items.LastEvaluatedKey != "undefined");

    return scanResults;

};

回答by Nicolas Hevia

AWS documentation example didn't work for me. @Hank approach did the trick.

AWS 文档示例对我不起作用。@Hank 方法成功了。

Using handler inside a lambda:

在 lambda 中使用处理程序：

const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient({
    // optional tuning - 50% faster(cold) / 20% faster(hot)
    apiVersion: '2012-08-10',
    sslEnabled: false,
    paramValidation: false,
    convertResponseTypes: false
});

const tableName = 'series';

exports.handler = async (event, context, callback) => {
    let params = { TableName: tableName };

    let scanResults = [];
    let items;

    do {
        items = await docClient.scan(params).promise();
        items.Items.forEach((item) => scanResults.push(item));
        params.ExclusiveStartKey = items.LastEvaluatedKey;
    } while (typeof items.LastEvaluatedKey != "undefined");

    callback(null, scanResults);
};

回答by Ioannis Tsiokos

Using Promises and async

使用承诺和异步

const aws = require('aws-sdk');
aws.config.update({ region: 'us-east-1' });
const documentClient = new aws.DynamoDB.DocumentClient();

const scanAll = async (params) => {
  let lastEvaluatedKey = 'dummy'; // string must not be empty
  const itemsAll = [];
  while (lastEvaluatedKey) {
    const data = await documentClient.scan(params).promise();
    itemsAll.push(...data.Items);
    lastEvaluatedKey = data.LastEvaluatedKey;
    if (lastEvaluatedKey) {
      params.ExclusiveStartKey = lastEvaluatedKey;
    }
  }
  return itemsAll;
}

Use like this

像这样使用

const itemsAll = scanAll(params);

The code is the same for query (just replace scan with query)

查询代码相同（只需将扫描替换为查询）

回答by Troy Ready

You can use the ScanPaginator from @aws/dynamodb-query-iterator:

您可以使用@aws/dynamodb-query-iterator 中的 ScanPaginator：

import { ScanPaginator } from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const paginator = new ScanPaginator(
  new DynamoDB.DocumentClient(),
  {
    TableName: "users",
    FilterExpression: "#user_status = :user_status_val",
    ExpressionAttributeNames: {
      "#user_status": "user_status",
    },
    ExpressionAttributeValues: { ":user_status_val": 'somestatus' }
  }
);

for await (const page of paginator) {
    // do something with `page`, e.g. myFunction(page.Items)
}

回答by Mazzaroth

I use promises like this:

我使用这样的承诺：

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

async function dbRead(params) {
    let promise = docClient.scan(params).promise();
    let result = await promise;
    let data = result.Items;
    if (result.LastEvaluatedKey) {
        params.ExclusiveStartKey = result.LastEvaluatedKey;
        data = data.concat(await dbRead(params));
    }
    return data;
}

and to use it:

并使用它：

let params = {
  TableName: 'Table'
};
let data = await dbRead(params);

回答by David White

A node express solution that returns the data in JSON format:

一个以JSON格式返回数据的节点快递解决方案：

let datapack=[];
item = {
        TableName: ddbTable,
        FilterExpression: "aws = :e AND begins_with ( Id, :t )",
        ExpressionAttributeValues: {
            ":t"    :   "contact",
            ":e"    :   aws
        },
        ProjectionExpression: "Id,FirstName,LastName,cEmail",
    };
    docClient.scan(item, onScan);
    function onScan(err, data) {
        if (err) {
            console.error("Unable to scan the table. Error JSON:", JSON.stringify(err, null, 2));
        } else {        
            datapack = datapack.concat(data.Items);
            });
            if (typeof data.LastEvaluatedKey != "undefined") {
                item.ExclusiveStartKey = data.LastEvaluatedKey;
                docClient.scan(item, onScan);
            } else {
                res.json(datapack);
            }
        }
    }

回答by David White

Here is an answer that will deliver indexed results rather than using an expensive scan, also in JSON format node/express. Note use of docClient.query:

这是一个将提供索引结果而不是使用昂贵的扫描的答案，也是 JSON 格式的节点/快递。注意 docClient.query 的使用：

 datapack=[];
    item = {
        TableName: ddbTable,
        IndexName: "cEmailIndex",
        KeyConditionExpression : "aws = :e AND begins_with ( cEmail, :t )",
        ExpressionAttributeValues: {
            ":t"    :   search,
            ":e"    :   aws
        },
        ProjectionExpression: "Id,FirstName,LastName,cEmail",
    };
    docClient.query(item, onScan);
    function onScan(err, data) {
        if (err) {
            console.error("Unable to scan the table. Error JSON:", JSON.stringify(err, null, 2));
        } else {
            datapack = datapack.concat(data.Items);
            if (typeof data.LastEvaluatedKey != "undefined") {
                item.ExclusiveStartKey = data.LastEvaluatedKey;
                docClient.query(item, onScan);
            } else {
                // console.log(JSON.stringify(datapack));
                res.json(datapack);
            }
        }
    }

回答by kalpa

const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient({
    // optional tuning - 50% faster(cold) / 20% faster(hot)
    apiVersion: '2012-08-10',
    sslEnabled: false,
    paramValidation: false,
    convertResponseTypes: false,
    region: 'us-east-2' // put your region
});
const tableName = 'tableName'; // put your tablename

exports.handler = async (event, context, callback) => {
    let params = { TableName: tableName };

    let scanResults = [];
    let items;

    do {
        items = await docClient.scan(params).promise();
        items.Items.forEach((item) => scanResults.push(item));
        params.ExclusiveStartKey = items.LastEvaluatedKey;
    } while (typeof items.LastEvaluatedKey != "undefined");

    callback(null, scanResults);
};