DynamoDB update item with conditionExpression instead of key

Question

I try to update an item in dynamodb by adding a condition, without passing the key in the parameters. And as soon as my condition is true update. Is it possible to do this?

Below an example of an item:

{
   "id" : "bcc2f32e-305e-4469-88e2-463724b5c6a9",
   "name" : "toto",
   "email" : "[email protected]"
}

Where email is unique for items.

I tested this code and it works :

const name= "updateName";
const params = {
    TableName: MY_TABLE,
    Key: {
        id
    },
    UpdateExpression: 'set #name = :name',
    ExpressionAttributeNames: { '#name': 'name' },
    ExpressionAttributeValues: { ':name': name },
    ReturnValues: "ALL_NEW"
}

dynamoDb.update(params, (error, result) => {
    if (error) {
        res.status(400).json({ error: 'Could not update Item' });
    }
    res.json(result.Attributes);
})

But i want to do something like this (replace the Key by conditionExpression):

const params = {
    TableName: MY_TABLE,
    UpdateExpression: 'set #name = :name',
    ConditionExpression: '#email = :email',
    ExpressionAttributeNames: { 
        '#name': 'name',
        '#email': 'email'   
    },
    ExpressionAttributeValues: { 
        ':name': name,
        ':email': email
    },
    ReturnValues: "ALL_NEW"
}
dynamoDb.update(params, (error, result) => {
    if (error) {
        res.status(400).json({ error: 'Could not update User' });
    }
    res.json(result.Attributes);
})

But this code doesn't work.

Any ideas?

Query (or scan) to locate the item first, retrieve its key, then update that item using the first method. Maybe a GSI on the email attribute to help query it quickly. — jarmod

gandaliter gandaliter · Accepted Answer · 2020-04-05T09:26:03

You cannot update an item in DynamoDB without using the entire primary key (partition key, and sort key if present). This is because you must specify exactly one record for the update. See the documentation here.

If you want to find an item using a field that is not the primary key, then you can search using a scan (potentially slow and expensive) or by using a Global Secondary Index (GSI) on that field. Either of these methods requires that you do a separate request to find the item in question, and then use its primary key to perform the update.

It sounds like you want to do an update that waits for a condition. That's not how DynamoDb works; it cannot wait for anything (except consistency, I suppose, but that's somewhat different). What you can do is make a request with a condition, and if it fails the condition (returning immediately), make the request again later. If you do this you'll need to be careful to backoff appropriately, or you might end up making a lot of requests very quickly.

DynamoDB update item with conditionExpression instead of key

2 Answers