Is there a way to enforce unique constraint on a property (field) other than the primary key in dynamodb

Short answer: No.

DynamoDB is a key:value store. It is very good at quickly retrieving/saving Items because it does a couple of compromise. This is a constraint you have to handle yourself.

Nonethess, depending on your actual model, it might be a good idea to use this field as you hash_key or consider using a range_key

If this is not possible, I advise you to de-normalize your data. You currently have something like:

UserTable

• hash_key: user_id
• e-mail
• ...

To ensure unicity, add a new table with this schema:

EmailUser

• hash_key: e-mail
• user_id

To make sure an e-mail is unique, just issue a GetItem to EmailUser before.

This kind of de-normalization is quite common with No-SQL databases.

There is no such way you can enforce uniqueness on other attribute but using python's boto3 library you can use client to do transact item and use some composite key and try to duplicate your entry and insert all of them in a single go using transact_write_items(). There is very nice documentation by aws on this: https://aws.amazon.com/fr/blogs/database/simulating-amazon-dynamodb-unique-constraints-using-transactions/