DynamoDBQuery

When we use the Low or High Level API constructors to create a query we end up with the type DynamoDBQuery which is a sealed trait.

One of the primary methods on this trait is execute which will run the query and return the result as a ZIO effect.

def execute: ZIO[DynamoDBExecutor, DynamoDBError, Out] = ???

The execute method requires a DynamoDBExecutor service in order to execute the query using the lower level ZIO AWS DynamoDB library.

The execute method does the following:

• if the query type is a composite (Zip) then it will automatically batch or parallelise the queries - see Auto batching and parallelisation for the exact rules
• executes the query using the DynamoDBExecutor service, which:
  • converts it to an underlying ZIO AWS DynamoDB query
  • converts the ZIO AWS DynamoDB response back to an Item (type alias for an AttrMap)

When using the High Level API transformations are done between the Scala model and the Item type using the automatically generated codecs that make use of the ZIO Schema in implicit scope.

The next sections cover the surface area exposed by DynamoDBQuery.

DynamoDBQuery Combinators and Operations

DynamoDBQuery Combinators	Alias	Description
map		map the result of a query with a function
zip	<*>	combine 2 queries together and returns a tuple - makes the resulting query eligible for automatic batching or parallelisation see Autobatching and Parallelisation for more details
zipWith		does a zip and then immediately maps the result with a function
zipLeft	<*	a zip that ignores the result of the right query
zipRight	*>	a zip that ignores the result of the left query

DynamoDBQuery Functions

Description

def forEach[In, A, B](values: Iterable[A])(body: A => DynamoDBQuery[In, B]): DynamoDBQuery[In, List[B]]

DynamoDB.forEach automates the zipping of queries of the same type using a collection as input. see Autobatching and Parallelisation for more details. Note that unprocessed items/keys are retried automatically and if they still fail a BatchError.WriteError/BatchError.GetError is returned both of which will contain a list of the unprocessed items/keys - see withRetryPolicy in the below section for overriding the default retry policy.

DynamoDBQuery Operations	Description
capacity	sets the ReturnConsumedCapacity. AWS API. Note capacity data in the response is ignored by the High Level Api
consistency	sets the ConsistencyMode for read operations. Valid values are Strongand Weak(default) AWS API
filter	sets the FilterExpression - applies to ScanSome, ScanAll, QuerySome, QueryAll. Note the filter is applies after the read by DDB so no read units are saved, however latency costs are reduced.
gsi	creates a Global Secondary Index - applies to a CreateTable query. AWS API
indexName	sets the local secondary index or global secondary index name - applies to ScanSome, ScanAll, QuerySome, QueryAll. AWS API
lsi	creates a local Secondary Index - applies to a CreateTable query. AWS API
metrics	set ReturnItemCollectionMetrics, valid values are None (default) and Size - applies to PutItem, UpdateItem, Delete, Transaction. Note that metric data in the response is ignored by the High Level API. AWS API
parallel(N)	Applies only to Scan - sements and runs the query in parallel in DDB and merges the items in the response. N is level of parallelism. AWS API.
returns	sets the ReturnValues - applies to UpdateItem, DeleteItem, PutItem (see Crud Operations reference section for each operation for more details). AWS API
selectAllAttributes, selectAllProjectedAttributes, selectSpecificAttributes, selectCount	Determines the attributes returned by Scan and Query AWS API
sortOrder	sets the sort order for Query's AWS API
startKey	Applies to Query and Scan and specifies the start key for the query. AWS API
transaction	executes the query in a transaction - see Transactions Guide for more details.
where	sets the ConditionExpression - applies to PutItem, DeleteOtem, UpdateItem and Scan AWS API
whereKey	set the KeyConditionExpr applies to QuerySome and QueryAll. AWS API
withClientRequestToken	set the client request token` - applies to write transactions AWS API
withRetryPolicy	override the default retry policy for a batched query - see Autobatching and Parallelisation for more details