Confused on querying DynamoDB - node.js

Question

I've the below data in my DynamoDB.
and I'm trying to achieve the below result.
scan through the table and get the rows where the management is NULL and Location is Midwest.
I initially tried the below query to match the 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);
}
}
}
I get the exception as
{
"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
}
please let me know where am I going wrong and how can I fix this.

Answer 1

Here is the scan item for "NULL" value (i.e. String attribute having NULL as data).
I assume that Management attribute is of String data type containing the string value "NULL".
Code:-
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);
}
}
}