Update item field in Amazon DynamoDB without overwriting other fields - amazon-web-services

Question

I have an Amazon DynamoDB table called "users' that has one user with the fields -UserId, FirstName, LastName, SignedInAt, SignedOutAt, IsSigned in.
I want to only update certain fields, not all, but when I execute the following code, the fields that I am not updating disappear.
So, I am just left with the UserID, SignedInAt, and IsSignedIn feilds. How do I update without the other fields disappearing?
I am using JavaScript.
Thanks!!!
Before executing code:
await dynamo
.put({
TableName: "users",
Item: {
UserId: requestJSON.UserId,
SignedInAt: new Date().toLocaleTimeString(), // 11:18:48 AM
IsSignedIn: true
}
})
.promise();
After:

Answer 1

The problem with your code is you are using the put method. To update an Amazon DynamoDB item, you need to call the updateItem method. Here is an example in Java V2 API (you can port this code to your programming language) that updates an item based on the key.
public static void updateTableItem(DynamoDbClient ddb,
String tableName,
String key,
String keyVal,
String name,
String updateVal){
HashMap<String,AttributeValue> itemKey = new HashMap<String,AttributeValue>();
itemKey.put(key, AttributeValue.builder().s(keyVal).build());
HashMap<String,AttributeValueUpdate> updatedValues =
new HashMap<String,AttributeValueUpdate>();
// Update the column specified by name with updatedVal
updatedValues.put(name, AttributeValueUpdate.builder()
.value(AttributeValue.builder().s(updateVal).build())
.action(AttributeAction.PUT)
.build());
UpdateItemRequest request = UpdateItemRequest.builder()
.tableName(tableName)
.key(itemKey)
.attributeUpdates(updatedValues)
.build();
try {
ddb.updateItem(request);
} catch (ResourceNotFoundException e) {
System.err.println(e.getMessage());
System.exit(1);
} catch (DynamoDbException e) {
System.err.println(e.getMessage());
System.exit(1);
}
// snippet-end:[dynamodb.java2.update_item.main]
System.out.println("Done!");
}

Answer 2

SOLVED
const AWS = require("aws-sdk");
const dynamo = new AWS.DynamoDB.DocumentClient();
exports.handler = async(event, context) => {
let body;
let user;
let statusCode = 200;
const headers = {
"Content-Type": "application/json"
};
try {
let requestJSON = JSON.parse(event.body);
switch (event.routeKey) {
case "GET /items":
body = await dynamo.scan({ TableName: "users" }).promise();
break;
case "PUT /signIn":
await dynamo
.update({
TableName: "users",
Key: {
UserId: requestJSON.UserId
},
UpdateExpression: "set SignedInAt = :a, IsSignedIn = :b, SignedOutAt = :c",
ExpressionAttributeValues: {
":a": new Date().toLocaleTimeString(),
":b": true,
":c": ""
}
})
.promise();
body = `Put item ${requestJSON.UserId}`;
break;
case "PUT /signOut":
await dynamo
.update({
TableName: "users",
Key: {
UserId: requestJSON.UserId
},
UpdateExpression: "set SignedOutAt = :a, IsSignedIn = :b",
ExpressionAttributeValues: {
":a": new Date().toLocaleTimeString(),
":b": false,
}
})
.promise();
body = `Put item ${requestJSON.UserId}`;
break;
default:
throw new Error(`Unsupported route: "${event.routeKey}"`);
}
}
catch (err) {
statusCode = 400;
body = err.message;
}
finally {
body = JSON.stringify(body);
}
return {
statusCode,
body,
headers
};
};