I am creating an app using a GraphQL API in AWS AppSync, with DynamoDB for storage. My DynamoDB table utilises a primary key only (id) and does not use a sort key. I want to ensure that new objects added to the table (with the same primary key / id) do not overwrite existing objects.
My lambda function handler contains the following code:
const params = {
TableName : "myTable",
Item: {
id: "4321",
name: event.arguments.input.name,
description: event.arguments.input.description
},
ConditionalExpression: 'attribute_not_exists(id)',
};
await documentClient.put(params, function(err, data) {
if (err) {
console.log(err);
callback(err);
} else {
callback(null, data)
}
}).promise();
According to multiple sources (1, 2, 3), the conditional expression attribute_not_exists(id) should prevent entries with the same id being added to the table, since this is the primary key and I do not have a sort key.
After adding the first object to the database, I expected that subsequent calls would fail, since I hardcoded the id field to check that objects cannot be overwritten with the same ID. However, I can see that the object is being updated in DynamoDB, as the non-key fields (name and description) are changing.
For additional context, I have been executing this mutation using the 'Run a Query' part of the AppSync console in the AWS management console. Then I check to see if the mutation is successful by looking at my DynamoDB tables in the AWS management console.
