How to Add a Column in DynamoDB

Well, let's not get dragged away in the semantic discussion about the difference between "fields" and "columns". The word "column" does remind us of relational databases, which dynamodb is not. In essence that means that dynamodb does not have foreign keys.

Dynamodb does have "primary partition keys" and "index partition keys" though, just as with relational databases. (Although there are other strategies as well)

You do need to respect those keys when you add data. But aside from those requirements, you don't have to predefine your fields (except for those partition keys mentioned earlier).

Assuming that you are new to this, some additional good practices:

• Add a numeric field to each record, to store the time of creation in seconds. Dynamodb has optional cleaning features, which require this type of field in your data.
• You cannot use dates in dynamodb, so you have to store those as numeric fields or as strings. Given the previously mentioned remark, you may prefer a numeric type for them.
• Don't store big documents in it, because there is a maximum fetch size of 16MB, and a maximum record size of 400KB. Fortunately, AWS has S3 storage and other kind of databases (e.g. DocumentDB).

There are many strategies for table keys:

• If you only declare the partition-key, then it acts like a primary key (e.g. partition-key=invoiceId). That's fine.
• If your object has a parent reference. (e.g. invoices have a customer), then you probably want to add a sort-key. (e.g. partition-key=customerId;sort-key=invoiceId) Together they behave like a composed key. The advantage is that you can do a lookup using both keys, or just using the partition-key. (e.g. request a specific invoice for a specific customer, or all invoices for that customer)

DynamoDB does not require schema definition, and so there is no such thing as a "column". You can just add a new item with a new attribute.