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I would like to 'upsert' a document in DynamoDB. That is, I would like to specify a key, and a set of field/value pairs. If no document exists with that key, I want one created with that key and the key/value pairs I specified. If a document exists with that key, I want the fields I specified to be set to the values specified (if those fields did not exist before, then they should be added). Any other, unspecified fields on the existing document should be left alone.
It seems I can do this pretty well with the UpdateItem call, when the field/value pairs I am setting are all top-level fields. If I have nested structures, UpdateItem will work to set the nested fields, as long as the structure exists. In other words, if my existing document has "foo": {}, then I can set "foo.bar": 42 successfully.
However, I don't seem to be able to set "foo.bar": 42 if there is no foo object already (like in the case where there is no document with the specified field at all, and my 'upsert' is behaving as an 'insert'.
I found a discussion on the AWS forums from a few years ago which seems to imply that what I want to do cannot be done, but I'm hoping this has changed recently, or maybe someone knows of a way to do it?
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UpdateItem behaves as an “UPSERT” operation. This means that if you try to update an item that doesn't exist, DynamoDB will automatically create it for you.
In addition to simple data types like numbers and strings DynamoDB supports these types: Nested object: A value of an attribute in DynamoDB can be a complex nested object. Set: A set of numbers, strings, or binary values.
The only way to update multiple items at the same time is use TransactionWrite operation provided by DynamoDB. But it comes with a limitation (25 at most for example). So keep in mind with that, you probable should do some limitation in your application as well.
Key-value and document data modelsThis enables DynamoDB to have a flexible schema, so each row can have any number of columns at any point in time. This allows you to easily adapt the tables as your business requirements change, without having to redefine the table schema as you would in relational databases.
UpdateItembehaves like an "upsert" operation: The item is updated if it exists in the table, but if not, a new item is added (inserted). http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/SQLtoNoSQL.UpdateData.html
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