Is it possible to atomically add several items to DynamoDB array with checking their occurance in it (to avoid duplication)? - amazon-web-services

Question

I have email black list stored as one item in DynamoDB
// item example
{
id: "blackList" // PrimaryKey of item
list: [ "email_1#example.com", "email_2#example.com" ]
}
It is possible to add new email to the list and the same time check if it's not already presented in the list (to avoid duplication) by atomic update:
const email = "email_new#example.com";
const params = {
TableName: "myTable",
Key: {
id: "blackList"
},
AttributeUpdates: {
list: {
Action: "ADD",
Value: [email] // several emails can also be added with incorrect Expected check
},
},
Expected: {
list: {
ComparisonOperator: "NOT_CONTAINS",
Value: email
},
}
};
await docClient.update(params).promise();
The question is whether it's possible to perform the same atomic operation for several emails at once?

Answer 1

Use a string set if you want there to be no duplicates. If you want to see if they existed in the set before you added them, return the old item.
const email = "email_new#example.com";
const params = {
TableName: "myTable",
Key: {
id: "blackList"
},
UpdateExpression: "ADD #email :email",
ExpressionAttributeNames: {
"#email": "email"
},
ExpressionAttributeValues: {
":email": docClient.createSet(email)
}
};
await docClient.update(params).promise();
This will add the email_new#example.com to the email attribute as a string set. If the email attribute doesn't exist on the object it will be created.
See https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.ADD for the documentation.