How to insert to DynamoDb just if the key does not exist - node.js

Question

I want to add id + some values to a DynamoDb just once. If the id exists already it should do nothing or update
I can go with
search
if not found > insert
if found > do nothing or update (for now do nothing is fine)
But hopfully there is a better way to do it. The id should be the key to check for.
That's the code in node:
const dynamodbParams = {
TableName: process.env.DYNAMODB_TABLE_BLICKANALYTICS,
Item: {
id: userId,
createdAt: timestamp
},
};
dynamoDb.put(dynamodbParams).promise()
.then(data => {
console.log('saved: ', dynamodbParams);
})
.catch(err => {
console.error(err);
});
I use this in yml. Don't know if there are options to set this up in yml
resources:
Resources:
DynamoDbTableExpenses:
Type: 'AWS::DynamoDB::Table'
DeletionPolicy: Retain
Properties:
AttributeDefinitions:
-
AttributeName: id
AttributeType: S
-
AttributeName: createdAt
AttributeType: N
KeySchema:
-
AttributeName: id
KeyType: HASH
-
AttributeName: createdAt
KeyType: RANGE
ProvisionedThroughput:
ReadCapacityUnits: 1
WriteCapacityUnits: 1
TableName: ${self:provider.environment.DYNAMODB_TABLE_BLICKANALYTICS}

Answer 1

You can do the whole thing with a single UpdateItem operation:
const dynamodbParams = {
TableName: process.env.DYNAMODB_TABLE_BLICKANALYTICS,
Key: {id: userId},
UpdateExpression: 'SET createdAt = if_not_exists(createdAt, :ca)',
ExpressionAttributeValues: {
':ca': {'S': timestamp}
}
};
dynamoDb.updateItem(params, function(err, data) {
if (err) {
console.log(err, err.stack);
} else {
console.log(data);
}
}
If you only want to do insert if not exists, you can easily do that with PutItem:
const dynamodbParams = {
TableName: process.env.DYNAMODB_TABLE_BLICKANALYTICS,
Item: {
id: userId,
createdAt: timestamp
},
ConditionExpression: 'attribute_not_exists(id)'
};
dynamodb.putItem(params, function(err, data) {
if (err) {
console.log(err, err.stack);
} else {
console.log(data);
}
}
You can come up with more complex ways how to set or update attributes in an item by combining the condition expressions and update expressions.
Note I have not fully tested the code, so please comment if there's any error, but it should work.