I have searched this on Google for a while but did not get a specific answer.
Lets say I have a table storing the people information, it uses PeopleId as the hash key. Is there a way to construct a query to return the person if his Id is 1 or 2?
Looks like I can use BatchGetItem to do such things, but will it have higher latency?
You cannot have any conditions of the Partition Key part of your Primary Key in DynamoDB. You can on the Sort Key.
So, you would either have to do GetItem twice, or use BatchGetItem.
Related
I have a table with a composite key; there is both a partition and a sort key. I know that the java sdk allows me to query by just the partition key. However, if I do this then the docs say I will get this iterator back ItemCollection<QueryOutcome>. This means for me to work with this data, I will have to iterate over the entire collection in order to fulfill my needs.
It would be easier if I was able to get back a Map<T, V> type where the key here would be the sort key. That way, I can quickly find rows for a particular sort key. Is this possible? I would rather not iterate over the collection just to find certain items with a certain sort key value.
If you just want an item with a certain sort key, that’s a get item. Don’t do a Query.
You may be confused by DynamoDB’s use of the word Query. That’s not the only way to query the database. It’s one way to query which happens to have the name Query.
In every cosmos db repository example I've seen, the id/row key has been generated like this: {partitionKey}:{Guid.newGuid()}. I'm working on a web api where the user won't necessarily have any way of knowing what this random GUID is. But they will know the EmployeeId, ProjectId etc. of the respective object, so I'm wondering if there are any issues with using i.e. EmployeeId as both the partition key and Id?
There's nothing technically wrong with the approach of setting id and partition key the same however you will have just one document per partition and that's bad design IMHO as all your read queries will be cross-partition queries (e.g. listing all employees).
One approach could be to set the partition key as the type of the entity (Employee, Project etc.) and then set the id as the unique identifier of the entity (employee id, project id etc.).
To be honest, if you know the partition key AND the item id, you can do a Point read which is the fastest.
We used to also take the approach of using random guids for all item IDs, but this means you will always need to know this id and partition key. Sometimes a more functional key as the item ID makes more sense so have a good thought about it!
And remember, an item ID is not unique, the uniqueness is only within the partition key.
So you could have two items with the same item ID and different partition key.
A bit of context: I am trying to build an inventory to list my AWS resources in various accounts and I am planning to use DynamoDB to store the data. These will be the columns for my table: ResourceARN, ResourceName, ResourceType, StandardTag, IsDeleted, LastUpdateTime and ResourceCreationDate ( this field is available only for a few resource types like Ec2).
Question: I want to query my DDB table using account ID, resource type and tag name. I am stumped on choosing the primary key for the table. Since primary key should be unique and has to have 1:many relationship. Hence, I cannot use a combination of resourceType and account Id. Nor can I use resourceArn as my primary key since it is 1:1 relationship. Also, using the resourceARN as the sort key does not make sense to me. I understand that I can use a simple scan operation, but that is very costly and will take time if I add more data in my DDB.
I would appreciate any suggestions or guidance over the same.
Short answer
Partition key: Account ID
Sort key: <resource type>/<resource ID>
Rationale
It's a common pattern for a sort key to be a string concatenating multiple attributes. Since sort keys can be queried by prefix, you can leverage this in your queries:
Get all account resources: query all sort keys on the Account ID partition key
Get all EC2 instances of an account: query with partition key = <your account ID> and sort key begins_with('ec2-instance').
You may notice that ARNs follow such a hierarchy as well (what's probably not a coincidence). This would be effectively using a subset of the ARN as the sort key.
Some notes:
DynamoDB is about attributes as much as about columns. You don't need to include ResourceCreationDate in the records which don't have it, and doing so will save you space (see next point).
Attribute names count as storage for every record, which impacts cost and also throughput. It's common to use shorthand for names for this reason (rct instead of ResourceCreationTime for example).
You can use LSIs (Local Secondary Indexes) to order by creation and update times if you need this.
select * from tableName where columnName="value";
How can I fetch a similar result in DynamoDB using java, without using primary key as my attribute (Need to group data based on a value for a particular column).
I have gone through articles regarding getbatchitems, QuerySpec but all these require me to pass the primary key.
Can someone give a lead here?
Short answer is you can't. Whenever you use the Query or GetItem operations in DynamoDB you must always supply the table or index primary key.
You have two options:
Perform a Scan operation on the table and filter by columnName="value". However this requires DynamoDB to look at every item in the table so it is likely to be slow and expensive.
Add a Global Secondary Index to your table. This will require you to define a primary key for the index that contains the columnName you want to query
It appears that dynamodb's query method must include the partition key as part of the filter. How can a query be performed if you do not know the partition key?
For example, you have a User table with the attribute userid set as the partition key. Now we want to look up a user by their phone number. Is it possible to perform the query without the partition key? Using the scan method, this goal can be achieved, but at the expense of pulling every item from the table before the filter is applied, as far as I know.
You'll need to set up a global secondary index (GSI), using your phoneNumber column as the index hash key.
You can create a GSI by calling UpdateTable.
Once you create the index, you'll be able to call Query with your IndexName, to pull user records based on the phone number.