I am studying DynamoDB and confuse on the order.
a. Could I use multiple conditions in the KeyConditions field of query command to do the 'AND' query? i.e. Set condition to the following keys:
hash part of primary key,
range part of primary key,
local secondary index 1,
b. If it's workable, how would DynamoDB sort the result?
DynamoDB can only use one index at a time so you can't really query using both a range primary key AND a secondary index.
The sort will be based on the index actually used.
The conditions are filtering out results and are not limited to indices.
Related
I have a DynamoDB table with following keys:
id: partition key
created_at: sort key
brand#category#size#color: partition key for global index 'byAttributes'
The global index partition key is a composite of 4 table attributes using '#' as a delimiter.
Is there a way in DynamoDB that I can query the table using only a subset of the attributes using a wildcard for unspecified attributes?
As examples:
byAttributes = 'levis#shirts#*#red'
byAttributes = '*#pants#L#*'
I don't wish to use a FilterExpression because it only filters data after a search. I want to take advantage of the attributes being indexed.
No. But you can create alternative GSIs for different combinations.
You can also include a hierarchical SK value and use begins-with to limit based on zero or more values.
Putting some values in the PK and the rest in a hierarchical SK achieves a lot of combinations.
For example have a GSI:
PK = category,
SK = size#brand#color
Now you can query by category, category/size, category/size/brand, or all four.
If it gets more than four you may want to look at Rockset as an indexing system against DynamoDB data.
I've got a list of partition keys from one table.
userId["123","456","235"]
I need to get an attribute that they all share. like "username".
What would be the best practice to get them all at once?
Is scan my only option knowing that I know all my partition keys?
Do I know the sort key? yes but only the beginning of it. Therefore I
don't think I could use batchGetItem.
Scan is only appropriate if you don't know the partition keys. Because you know the partition keys you want to search, you can achieve the desired behavior with multiple Query operations.
A Query searches all documents with the specified partition key; you can only query one partition key per request, so you'll need multiple queries, but this will still be significantly more efficient than a single Scan operation.
If you're only looking for documents with a sort key that begins with something, you can include it in your KeyConditionExpression along with the partition key.
For example, if you wanted to only return documents whose sort key begins with a certain string, you could pass something like userId = :user_id AND begins_with(#SortKey, :str) as the key condition expression.
You can efficiently achieve the result by using PartQL SELECT statement. It allows to query array of partition keys with IN operator and apply additional conditions on other attributes without causing a full table scan.
To ensure that a SELECT statement does not result in a full table
scan, the WHERE clause condition must specify a partition key. Use the
equality or IN operator.
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
Is it possible to retrieve rows from the dynamodb Global secondary index using batchgetitem api? If my aim is to retrieve data from the main table based on some non-key attribute also , but data should be retrieved in the batch of 100 items - is the GSI index won't fit here?
Also is BatchItemGet API available for Query? Say a table has the primary key and sort key and same primary key can have multiple sort keys can I retrieve multiple primary keys using batchItemGet with just primary key only or it won't fir here?
There is no way to specify the index name in the BatchGetItem API operation according to the docs. That means using BatchGetItem (and GetItem for that matter) on a secondary index isn't possible. Both of these operate on the primary index.
If you want to retrieve data from a secondary index, you need to use Query or Scan. Both support the IndexName attribute according to the documentation. When using Query you have to specify the partition key and can optionally filter based on the sort key. If you don't filter on the sort key, you will get all items with the partition key, which should take care of your second requirement.
To retrieve data from a secondary index based on different partition keys, you'd need to issue multiple Query operations for the separate values of these keys, there is no batching here.
You can use PartiQL with WHERE IN clause for that:
SELECT * FROM Orders WHERE OrderID IN [100, 300, 234]
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ql-reference.select.html
I'm using dynamo db, I was reading this document Class QueryRequest and says literately:
You can narrow the scope of the query by using comparison operators on
the range key value, or on the index key. You can use the
ScanIndexForward parameter to get results in forward or reverse order,
by range key or by index key.
But, I need know if is possible to sort my data according to another parameter (different to hash or range).
Thanks in advance.
You can only Query a Table of type Hash and Range, or a Local Secondary Index or a Global Secondary Index. You have to create the Table with the indexes, so if you haven't then you cannot query on them.