I am trying to query a dynamodb table. When I'm using the begins with operator I'm getting the following error.
{u'Message': u'All queries must have a condition on the hash key, and
it must be of type EQ', u'__type':
u'com.amazon.coral.validate#ValidationException'}
result_set = tb_places.query_2(
place_name__beginswith="ame",
)
Here place_name is a Global Secondary Index
Regardless if you are querying a table or index, the only operator that can be applied to a Hash Key attribute is the EQ. Alternatively, you could use BEGINS_WITH on a Range Key.
For a query on a table, you can have conditions only on the table
primary key attributes. You must provide the hash key attribute name
and value as an EQ condition. You can optionally provide a second
condition, referring to the range key attribute.[...]
For a query on an index, you can have conditions only on the index key
attributes. You must provide the index hash attribute name and value
as an EQ condition. You can optionally provide a second condition,
referring to the index key range attribute.
Source: http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Query.html
Related
I like to write a dynamoDb query in which I filter for a certain field, sounds simple.
All the examples I find always include the partition key value, which really confuses me, since it is unique value, but I want a list.
I got id as the partition key and no sort key or any other index. I tried to add partner as an index did not make any difference.
AttributeValue attribute = AttributeValue.builder()
.s(partner)
.build();
Map<String, AttributeValue> expressionValues = new HashMap<>();
expressionValues.put(":value", attribute);
Expression expression = Expression.builder()
.expression("partner = :value")
.expressionValues(expressionValues)
.build();
QueryConditional queryConditional = QueryConditional
.keyEqualTo(Key.builder()
.partitionValue("id????")
.build());
Iterator<Product> results = productTable.query(r -> r.queryConditional(queryConditional)
Would appreciate any help. Is there a misunderstandig on my side?
DynamoDB has two distinct, but similar, operations - Query and Scan:
Scan is for reading the entire table, including all partition keys.
Query is for reading a specific partition key - and all sort key in it (or a contiguous range of sort key - hence the nickname "range key" for that key).
If your data model does not have a range key, Query is not relevant for you - you should use Scan.
However this means that each time you call this query, the entire table will be read. Unless your table is tiny, this doesn't make economic sense, and you should reconsider your data model. For example, if you frequently look up results by the "partner" attribute, you can consider creating a GSI (global secondary index) with "partner" as its partition key, allowing you to quickly and cheapy fetch the list of items with a given "partner" value without scanning the entire table.
AWS DynamoDB table has :
Client (Primary Key),
folder_location (non-key attribute),
script_name (non-key attribute)
I want to retrieve records using Client and folder_location attributes using BatchGetItemRequest.
But getting below error:
Failed to retrieve items.com.amazonaws.services.dynamodbv2.model.AmazonDynamoDBException: The provided key element does not match the schema (Service: AmazonDynamoDBv2; Status Code: 400; Error Code: ValidationException;
Is there a way to do with BatchGetItemRequest only ?
You could instead use a Query or Scan operation and specify a Filter Expression to limit results based on the folder_location.
To use BatchGetItemRequest you must provide the key, per https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_BatchGetItem.html:
The BatchGetItem operation returns the attributes of one or more items
from one or more tables. You identify requested items by primary key.
Keys - An array of primary key attribute values that define specific
items in the table. For each primary key, you must provide all of the
key attributes. For example, with a simple primary key, you only need
to provide the partition key value. For a composite key, you must
provide both the partition key value and the sort key value.
I recommend you double check that the key you are providing matches the key defined in the table (name and data type). If so, then try one of those other options with a FilterExpression.
I have a DynamoDB table with partition key as userID and no sort key.
The table also has a timestamp attribute in each item. I wanted to retrieve all the items having a timestamp in the specified range (regardless of userID i.e. ranging across all partitions).
After reading the docs and searching Stack Overflow (here), I found that I need to create a GSI for my table.
Hence, I created a GSI with the following keys:
Partition Key: userID
Sort Key: timestamp
I am querying the index with Java SDK using the following code:
String lastWeekDateString = getLastWeekDateString();
AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();
DynamoDB dynamoDB = new DynamoDB(client);
Table table = dynamoDB.getTable("user table");
Index index = table.getIndex("userID-timestamp-index");
QuerySpec querySpec = new QuerySpec()
.withKeyConditionExpression("timestamp > :v_timestampLowerBound")
.withValueMap(new ValueMap()
.withString(":v_timestampLowerBound", lastWeekDateString));
ItemCollection<QueryOutcome> items = index.query(querySpec);
Iterator<Item> iter = items.iterator();
while (iter.hasNext()) {
Item item = iter.next();
// extract item attributes here
}
I am getting the following error on executing this code:
Query condition missed key schema element: userID
From what I know, I should be able to query the GSI using only the sort key without giving any condition on the partition key. Please help me understand what is wrong with my implementation. Thanks.
Edit: After reading the thread here, it turns out that we cannot query a GSI with only a range on the sort key. So, what is the alternative, if any, to query the entire table by a range query on an attribute? One suggestion I found in that thread was to use year as the partition key. This will require multiple queries if the desired range spans multiple years. Also, this does not distribute the data uniformly across all partitions, since only the partition corresponding to the current year will be used for insertions for one full year. Please suggest any alternatives.
When using dynamodb Query operation, you must specify at least the Partition key. This is why you get the error that userId is required. (In the AWS Query docs)
The condition must perform an equality test on a single partition key value.
The only way to get items without the Partition Key is by doing a Scan operation (but this wont be sorted by your sort key!)
If you want to get all the items sorted, you would have to create a GSI with a partition key that will be the same for all items you need (e.g. create a new attribute on all items, such as "type": "item"). You can then query the GSI and specify #type=:item
QuerySpec querySpec = new QuerySpec()
.withKeyConditionExpression(":type = #item AND timestamp > :v_timestampLowerBound")
.withKeyMap(new KeyMap()
.withString("#type", "type"))
.withValueMap(new ValueMap()
.withString(":v_timestampLowerBound", lastWeekDateString)
.withString(":item", "item"));
Always good solution for any customised querying requirements with DDB is to have right primary key scheme design for GSI.
In designing primary key of DDB, the main principal is that hash key should be designed for partitioning entire items, and sort key should be designed for sorting items within the partition.
Having said that, I recommend you to use year of timestamp as a hash key, and month-date as a sort key.
At most, the number of query you need to make is just 2 at max in this case.
you are right, you should avoid filtering or scanning as much as you can.
So for example, you can make the query like this If the year of start date and one of end date would be same, you need only one query:
.withKeyConditionExpression("#year = :year and #month-date > :start-month-date and #month-date < :end-month-date")
and else like this:
.withKeyConditionExpression("#year = :start-year and #month-date > :start-month-date")
and
.withKeyConditionExpression("#year = :end-year and #month-date < :end-month-date")
Finally, you should union the result set from both queries.
This consumes only 2 read capacity unit at most.
For better comparison of sort key, you might need to use UNIX timestamp.
Thanks
I have Tags as partition key in my table, and when I am trying to query I am getting AttributeError.
Below is my code:
kb_table = boto3.resource('dynamodb').Table('table_name')
result = kb_table.query(
KeyConditionExpression=Key('Tags').contains('search term')
)
return result['Items']
Error:
"errorMessage": "'Key' object has no attribute 'contains'"
Basically I want to search through the table where I the field is having that search term. I have achived it using scan but I have read everywhere that we should not use that.
result = kb_table.scan(
FilterExpression="contains (Tags, :titleVal)",
ExpressionAttributeValues={ ":titleVal": "search term" }
)
So I have changed my partition-key to Tags along with a sort-key so that I can achieve this using query but now I am getting this error.
Any idea how to get this working?
In order to use Query you must specify one partition to access, you cannot wildcard a partition or specify multiple keys.
KeyConditionExpression
The condition that specifies the key value(s)
for items to be retrieved by the Query action.
The condition must perform an equality test on a single partition key
value.
Assuming you want to search the whole table for tags, a scan is the most appropriate approach.
EDIT: You can use Query with the exact search term, but im guessing that is not what you want.
kb_table = boto3.resource('dynamodb').Table('table_name')
result = kb_table.query(
KeyConditionExpression=Key('Tags').eq('search term')
)
return result['Items']
Hi I have a dynamodb table. I want the service to return me all the items in this table and the order is by sorting on one attribute.
Do I need to create a global secondary index for this? If that is the case, what should be the hash key, what is the range key?
(Note that query on gsi must specify a "EQ" comparator on the hash key of GSI.)
Thanks a lot!
Erben
If you know the HashKey, then any query will return the items sorted by Range key. From the documentation:
Query results are always sorted by the range key. If the data type of the range key is Number, the results are returned in numeric order. Otherwise, the results are returned in order of UTF-8 bytes. By default, the sort order is ascending. To reverse the order, set the ScanIndexForward parameter set to false.
Now, if you need to return all the items, you should use a scan. You cannot order the results of a scan.
Another option is to use a GSI (example). Here, you see that the GSI contains only HashKey. The results I guess will be in sorted order of this key (I didn't check this part in a program yet!).
As of now the dynamoDB scan cannot return you sorted results.
You need to use a query with a new global secondary index (GSI) with a hashkey and range field. The trick is to use a hashkey which is assigned the same value for all data in your table.
I recommend making a new field for all data and calling it "Status" and set the value to "OK", or something similar.
Then your query to get all the results sorted would look like this:
{
TableName: "YourTable",
IndexName: "Status-YourRange-index",
KeyConditions: {
Status: {
ComparisonOperator: "EQ",
AttributeValueList: [
"OK"
]
}
},
ScanIndexForward: false
}
The docs for how to write GSI queries are found here: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/GSI.html#GSI.Querying
Approach I followed to solve this problem is by creating a Global Secondary Index as below. Not sure if this is the best approach but posting it if it is useful to someone.
Hash Key | Range Key
------------------------------------
Date value of CreatedAt | CreatedAt
Limitation imposed on the HTTP API user to specify the number of days to retrieve data, defaults to 24 hr.
This way, I can always specify the HashKey as Current date's day and RangeKey can use > and < operators while retrieving. This way the data is also spread across multiple shards.