Hi iam new in dynamo db and, with my knowledge its a non relational db ie we cant join the tables. My doubt is how we design the table structure. Please clarify with following example.
I have a following tables
1) users – user_id, username, password, email, phone number, role
2) roles – id, name [ie admin, supervisor, ect..]
a) My first doubt is we have any provision to set auto increment for user_id fields ?
b) Is this correct way of setting primary key as user_id?
c) Is this is the correct method to store user role in dynamo db? ie a roles table contains id and title and store role id in user table?
e) Is this possible to retrieve two tables data along with each user? Am using rails 3 and aws-sdk gem
If anybody reply it will be very helpful for me like a new dynamodb user
Typically with nosql style databases you would provide the unique identifier, rather than having an auto increment PK field do that for you. This usually would mean that you would have a GUID be the key for each User record.
As far as the user roles, there are many ways to accomplish this and each has benefits and problems:
One simple way would be to add a “Role” attribute to the Users table and have one entry per role for that user. Then you could grab the User and you would have all the roles in one query. DynamoDB allows attributes to have multiple values, so one attribute can have one value per role.
If you need to be able to query users in a particular role (ie. “Give me all the Users who are Supervisors”) then you will be doing a table scan in DynamoDB, which can be an expensive operation. But, if your number of users is reasonably small, and if the need to do this kind of lookup is infrequent, this still may be acceptable for your application.
If you really need to do this expensive type of lookup often, then you will need to create a new table something like “RolesWithUsers” having one record per Role, with the userIds of the users in the role record. For most applications I’d advise against doing something like this, because now you have two tables representing one fact: what role does a particular user have. So, delete or update needs to be done in two places each time. Not impossible to do, but it takes more vigilance and testing to be sure your application doesn’t get wrong data. The other disadvantage of this approach is that you need two queries to get the information, which may be more expensive than the table scan, again, depending on the quantity of records.
Another option that makes sense for this specific use case would be to use SimpleDb. It has better querying capability (all attributes are indexed by default) and the single table with roles as multi-valued attribute is going to be a much better solution than DynamoDB in this case.
Hope this helps!