查询DynamoDB时感到困惑

Question

我的DynamoDB中有以下数据。

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我正在努力实现下面的结果。浏览整个表并获取management is NULL and Location is Midwest所在位置的行。

我最初尝试使用下面的查询来匹配Null。

var scanningParameters = {
    TableName: 'LOB',
    FilterExpression: "#mgmt contains NULL",
    ExpressionAttributeNames: {
        "#mgmt": "Management",
    }
};

docClient.scan(scanningParameters, onScan);
function onScan(err, data) {
    if (err) {
        console.error("Unable to scan the table. Error JSON:", JSON.stringify(err, null, 2));
    } else {
        // print all the movies
        console.log("Scan succeeded.");
        data.Items.forEach(function (data) {
            console.log(
                data.lineofbusiness + " name : ",
                data.name);
        });

        if (typeof data.LastEvaluatedKey != "undefined") {
            console.log("Scanning for more...");
            scanningParameters.ExclusiveStartKey = data.LastEvaluatedKey;
            docClient.scan(scanningParameters, onScan);
        }
    }
}

我得到的异常是

{
    "message": "Invalid FilterExpression: Syntax error; token: \"contains\", near: \"#mgmtcontains NULL\"",
    "code": "ValidationException",
    "time": "2017-05-03T13:21:11.611Z",
    "requestId": "0T0GU59HRJ24P96D42H9QNC97RVV4KQNSO5AEMVJF66Q9ASUAAJG",
    "statusCode": 400,
    "retryable": false,
    "retryDelay": 13.73953651636839
}

请让我知道我哪里错了，以及我如何解决这个问题。

Answer 1

这是" NULL "值的扫描项目(即数据为NULL的字符串属性)。

我假设Management属性是包含字符串值"NULL“的字符串数据类型。

代码：-

var AWS = require("aws-sdk");
var creds = new AWS.Credentials('akid', 'secret', 'session');

AWS.config.update({
    region: "us-west-2",
    endpoint: "http://localhost:8000",
    credentials : creds
});

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

var params = {
    TableName: "lob",
    FilterExpression: "#mgmt = :mgmtVal",
    ExpressionAttributeNames: {
        "#mgmt": "Management",
    },
    ExpressionAttributeValues : {
        ":mgmtVal" : "NULL"
    }
};

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));
        });

        if (typeof data.LastEvaluatedKey != "undefined") {
            params.ExclusiveStartKey = data.LastEvaluatedKey;
            docClient.scan(params, onScan);
        }
    }
}