software.amazon.awssdk.extensions.dynamodb.mappingclient.extensions

Class ChainMapperExtension

java.lang.Object

software.amazon.awssdk.extensions.dynamodb.mappingclient.extensions.ChainMapperExtension

All Implemented Interfaces:

MapperExtension

public class ChainMapperExtension
extends Object
implements MapperExtension

A meta-extension that allows multiple extensions to be chained in a specified order to act as a single composite extension. The order in which extensions will be used depends on the operation, for write operations they will be called in forward order, for read operations they will be called in reverse order. For example :- If you create a chain of three extensions: ChainMapperExtension.of(extension1, extension2, extension3); When performing any kind of write operation (eg: PutItem, UpdateItem) the beforeWrite() method will be called in forward order: extension1 -> extension2 -> extension3 So the output of extension1 will be passed into extension2, and then the output of extension2 into extension3 and so on. For operations that read (eg: GetItem, UpdateItem) the afterRead() method will be called in reverse order: extension3 -> extension2 -> extension1 This is designed to create a layered pattern when dealing with multiple extensions. One thing to note is that UpdateItem acts as both a write operation and a read operation so the chain will be called both ways within a single operation.

Method Summary

Modifier and Type	Method and Description
ReadModification	afterRead(Map<String,AttributeValue> item, OperationContext operationContext, TableMetadata tableMetadata) Implementation of the MapperExtension interface that will call all the chained extensions in reverse order, passing the results of each one to the next and coalescing the results into a single modification.
WriteModification	beforeWrite(Map<String,AttributeValue> item, OperationContext operationContext, TableMetadata tableMetadata) Implementation of the MapperExtension interface that will call all the chained extensions in forward order, passing the results of each one to the next and coalescing the results into a single modification.
static ChainMapperExtension	of(MapperExtension... mapperExtensions) Construct a new instance of ChainMapperExtension.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

of

public static ChainMapperExtension of(MapperExtension... mapperExtensions)

Construct a new instance of ChainMapperExtension.

Parameters:

mapperExtensions - A list of MapperExtension to chain together.

Returns:

A constructed ChainMapperExtension object.

beforeWrite

public WriteModification beforeWrite(Map<String,AttributeValue> item,
                                     OperationContext operationContext,
                                     TableMetadata tableMetadata)

Implementation of the MapperExtension interface that will call all the chained extensions in forward order, passing the results of each one to the next and coalescing the results into a single modification. Multiple conditional statements will be separated by the string " AND ". Expression values will be coalesced unless they conflict in which case an exception will be thrown.

Specified by:

beforeWrite in interface MapperExtension

Parameters:

item - The AttributeValue map of the item to be written.

tableMetadata - A TableMetadata object describing the structure of the modelled table.

operationContext - The context under which the operation to be modified is taking place.

Returns:

A single WriteModification representing the coalesced results of all the chained extensions.

afterRead

public ReadModification afterRead(Map<String,AttributeValue> item,
                                  OperationContext operationContext,
                                  TableMetadata tableMetadata)

Implementation of the MapperExtension interface that will call all the chained extensions in reverse order, passing the results of each one to the next and coalescing the results into a single modification.

Specified by:

afterRead in interface MapperExtension

Parameters:

item - The AttributeValue map of the item that is being read.

tableMetadata - A TableMetadata object describing the structure of the modelled table.

operationContext - The context under which the operation to be modified is taking place.

Returns:

A single ReadModification representing the final transformation of all the chained extensions.