/*
* Copyright 2011-2012 Amazon Technologies, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
*
* http://aws.amazon.com/apache2.0
*
* This file is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES
* OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and
* limitations under the License.
*/
package com.amazonaws.services.dynamodb.datamodeling;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.text.ParseException;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import com.amazonaws.AmazonClientException;
import com.amazonaws.AmazonWebServiceRequest;
import com.amazonaws.services.dynamodb.AmazonDynamoDB;
import com.amazonaws.services.dynamodb.datamodeling.DynamoDBMapperConfig.ConsistentReads;
import com.amazonaws.services.dynamodb.datamodeling.DynamoDBMapperConfig.SaveBehavior;
import com.amazonaws.services.dynamodb.datamodeling.internal.PaginatedQueryList;
import com.amazonaws.services.dynamodb.datamodeling.internal.PaginatedScanList;
import com.amazonaws.services.dynamodb.model.AttributeValue;
import com.amazonaws.services.dynamodb.model.AttributeValueUpdate;
import com.amazonaws.services.dynamodb.model.ConditionalCheckFailedException;
import com.amazonaws.services.dynamodb.model.DeleteItemRequest;
import com.amazonaws.services.dynamodb.model.ExpectedAttributeValue;
import com.amazonaws.services.dynamodb.model.GetItemRequest;
import com.amazonaws.services.dynamodb.model.GetItemResult;
import com.amazonaws.services.dynamodb.model.Key;
import com.amazonaws.services.dynamodb.model.PutItemRequest;
import com.amazonaws.services.dynamodb.model.QueryRequest;
import com.amazonaws.services.dynamodb.model.QueryResult;
import com.amazonaws.services.dynamodb.model.ScanRequest;
import com.amazonaws.services.dynamodb.model.ScanResult;
import com.amazonaws.services.dynamodb.model.UpdateItemRequest;
import com.amazonaws.util.VersionInfoUtils;
/**
* Object mapper for domain-object interaction with DynamoDB.
* <p>
* To use, annotate domain classes with the annotations found in the
* com.amazonaws.services.dynamodb.datamodeling package. A minimal example:
*
* <pre>
* @DynamoDBTable(tableName = "TestTable")
* public class TestClass {
*
* private Long key;
* private double rangeKey;
* private Long version;
*
* private Set<Integer> integerSetAttribute;
*
* @DynamoDBHashKey
* public Long getKey() {
* return key;
* }
*
* public void setKey(Long key) {
* this.key = key;
* }
*
* @DynamoDBRangeKey
* public double getRangeKey() {
* return rangeKey;
* }
*
* public void setRangeKey(double rangeKey) {
* this.rangeKey = rangeKey;
* }
*
* @DynamoDBAttribute(attributeName = "integerSetAttribute")
* public Set<Integer> getIntegerAttribute() {
* return integerSetAttribute;
* }
*
* public void setIntegerAttribute(Set<Integer> integerAttribute) {
* this.integerSetAttribute = integerAttribute;
* }
*
* @DynamoDBVersionAttribute
* public Long getVersion() {
* return version;
* }
*
* public void setVersion(Long version) {
* this.version = version;
* }
* }
* </pre>
* <p>
* Save instances of annotated classes to DynamoDB, retrieve them, and delete
* them using the {@link DynamoDBMapper} class, as in the following example.
*
* <pre>
* DynamoDBMapper mapper = new DynamoDBMapper(dynamoDBClient);
* Long hashKey = 105L;
* double rangeKey = 1.0d;
* TestClass obj = mapper.load(TestClass.class, hashKey, rangeKey);
* obj.getIntegerAttribute().add(42);
* mapper.save(obj);
* mapper.delete(obj);
* </pre>
* <p>
* When using the save, load, and delete methods, {@link DynamoDBMapper} will
* throw {@link DynamoDBMappingException}s to indicate that domain classes are
* incorrectly annotated or otherwise incompatible with this class. Service
* exceptions will always be propagated as {@link AmazonClientException}, and
* DynamoDB-specific subclasses such as {@link ConditionalCheckFailedException}
* will be used when possible.
*
* @see DynamoDBTable
* @see DynamoDBHashKey
* @see DynamoDBRangeKey
* @see DynamoDBAutoGeneratedKey
* @see DynamoDBAttribute
* @see DynamoDBVersionAttribute
* @see DynamoDBIgnore
* @see DynamoDBMarshalling
* @see DynamoDBMapperConfig
*/
public class DynamoDBMapper {
private final AmazonDynamoDB db;
private final DynamoDBMapperConfig config;
private static final DynamoDBReflector reflector = new DynamoDBReflector();
/**
* User agent for requests made using the {@link DynamoDBMapper}. Intended
* for internal use only.
*/
public static final String USER_AGENT = DynamoDBMapper.class.getName() + "/" + VersionInfoUtils.getVersion();
/**
* Constructs a new mapper with the service object given, using the default
* configuration.
*
* @param dynamoDB
* The service object to use for all service calls.
* @see DynamoDBMapperConfig#DEFAULT
*/
public DynamoDBMapper(AmazonDynamoDB dynamoDB) {
this(dynamoDB, DynamoDBMapperConfig.DEFAULT);
}
/**
* Constructs a new mapper with the service object and configuration given.
*
* @param dynamoDB
* The service object to use for all service calls.
* @param config
* The default configuration to use for all service calls. It can
* be overridden on a per-operation basis.
*/
public DynamoDBMapper(AmazonDynamoDB dynamoDB, DynamoDBMapperConfig config) {
this.db = dynamoDB;
this.config = config;
}
/**
* Loads an object with the hash key given and a configuration override.
* This configuration overrides the default provided at object construction.
*
* @see DynamoDBMapper#load(Class, Object, Object, DynamoDBMapperConfig)
*/
public <T extends Object> T load(Class<T> clazz, Object hashKey, DynamoDBMapperConfig config) {
return load(clazz, hashKey, null, config);
}
/**
* Loads an object with the hash key given, using the default configuration.
*
* @see DynamoDBMapper#load(Class, Object, Object, DynamoDBMapperConfig)
*/
public <T extends Object> T load(Class<T> clazz, Object hashKey) {
return load(clazz, hashKey, null, config);
}
/**
* Loads an object with a hash and range key, using the default
* configuration.
*
* @see DynamoDBMapper#load(Class, Object, Object, DynamoDBMapperConfig)
*/
public <T extends Object> T load(Class<T> clazz, Object hashKey, Object rangeKey) {
return load(clazz, hashKey, rangeKey, config);
}
/**
* Returns an object with the given hash key, or null if no such object
* exists.
*
* @param clazz
* The class to load, corresponding to a DynamoDB table.
* @param hashKey
* The key of the object.
* @param rangeKey
* The range key of the object, or null for tables without a
* range key.
* @param config
* Configuration for the service call to retrieve the object from
* DynamoDB. This configuration overrides the default given at
* construction.
*/
public <T extends Object> T load(Class<T> clazz, Object hashKey, Object rangeKey, DynamoDBMapperConfig config) {
if ( config != this.config )
config = new DynamoDBMapperConfig(this.config, config);
String tableName = getTableName(clazz, config);
// Fill in the hash key element in the service request
Method hashKeyGetter = reflector.getHashKeyGetter(clazz);
AttributeValue hashKeyElement = getHashKeyElement(hashKey, hashKeyGetter);
// Determine the range key, if provided
AttributeValue rangeKeyElement = null;
if ( rangeKey != null ) {
Method rangeKeyMethod = reflector.getRangeKeyGetter(clazz);
if ( rangeKeyMethod == null ) {
throw new DynamoDBMappingException("Zero-parameter range key property must be annotated with "
+ DynamoDBRangeKey.class);
}
rangeKeyElement = getRangeKeyElement(rangeKey, rangeKeyMethod);
}
GetItemResult item = db.getItem(applyUserAgent(new GetItemRequest().withTableName(tableName)
.withKey(new Key().withHashKeyElement(hashKeyElement).withRangeKeyElement(rangeKeyElement))
.withConsistentRead(config.getConsistentReads() == ConsistentReads.CONSISTENT)));
Map<String, AttributeValue> itemAttributes = item.getItem();
if ( itemAttributes == null ) {
return null;
}
return marshallIntoObject(clazz, itemAttributes);
}
private <T> String getTableName(Class<T> clazz, DynamoDBMapperConfig config) {
DynamoDBTable table = reflector.getTable(clazz);
String tableName = table.tableName();
if ( config.getTableNameOverride() != null ) {
tableName = config.getTableNameOverride().getTableName();
}
return tableName;
}
private AttributeValue getHashKeyElement(Object hashKey, Method hashKeyGetter) {
AttributeValue hashKeyElement = new AttributeValue();
Class<?> hashKeyMethodReturnType = hashKeyGetter.getReturnType();
if ( hashKeyMethodReturnType.isPrimitive() || Number.class.isAssignableFrom(hashKeyMethodReturnType) ) {
hashKeyElement.setN(String.valueOf(hashKey));
} else if ( String.class.isAssignableFrom(hashKeyMethodReturnType) ) {
hashKeyElement.setS(String.valueOf(hashKey));
} else {
throw new DynamoDBMappingException("Hash key property must be either a Number or a String");
}
return hashKeyElement;
}
private AttributeValue getRangeKeyElement(Object rangeKey, Method rangeKeyMethod) {
AttributeValue rangeKeyElement = new AttributeValue();
Class<?> rangeKeyMethodReturnType = rangeKeyMethod.getReturnType();
if ( rangeKeyMethodReturnType.isPrimitive() || Number.class.isAssignableFrom(rangeKeyMethodReturnType) ) {
rangeKeyElement.setN(String.valueOf(rangeKey));
} else if ( String.class.isAssignableFrom(rangeKeyMethodReturnType) ) {
rangeKeyElement.setS(String.valueOf(rangeKey));
} else {
throw new DynamoDBMappingException("Range key property must be either a Number or a String");
}
return rangeKeyElement;
}
/**
* Creates and fills in the attributes on an instance of the class given
* with the attributes given.
* <p>
* This is accomplished by looking for getter methods annotated with an
* appropriate annotation, then looking for matching attribute names in the
* item attribute map.
*
* @param clazz
* The class to instantiate and hydrate
* @param itemAttributes
* The set of item attributes, keyed by attribute name.
*/
public <T> T marshallIntoObject(Class<T> clazz, Map<String, AttributeValue> itemAttributes) {
T toReturn = null;
try {
toReturn = clazz.newInstance();
} catch ( InstantiationException e ) {
throw new DynamoDBMappingException("Failed to instantiate new instance of class", e);
} catch ( IllegalAccessException e ) {
throw new DynamoDBMappingException("Failed to instantiate new instance of class", e);
}
if ( itemAttributes == null || itemAttributes.isEmpty() )
return toReturn;
for ( Method m : reflector.getRelevantGetters(clazz) ) {
String attributeName = reflector.getAttributeName(m);
if ( itemAttributes.containsKey(attributeName) ) {
setValue(toReturn, m, itemAttributes.get(attributeName));
}
}
return toReturn;
}
/**
* Sets the value in the return object corresponding to the service result.
*/
private <T> void setValue(final T toReturn, final Method getter, AttributeValue value) {
Method setter = reflector.getSetter(getter);
ArgumentUnmarshaller unmarhsaller = reflector.getArgumentUnmarshaller(toReturn, getter, setter);
unmarhsaller.typeCheck(value, setter);
Object argument;
try {
argument = unmarhsaller.unmarshall(value);
} catch ( IllegalArgumentException e ) {
throw new DynamoDBMappingException("Couldn't unmarshall value " + value + " for " + setter, e);
} catch ( ParseException e ) {
throw new DynamoDBMappingException("Error attempting to parse date string " + value + " for "+ setter, e);
}
safeInvoke(setter, toReturn, argument);
}
/**
* Returns an {@link AttributeValue} corresponding to the getter and return
* result given, treating it as a non-versioned attribute. Only useful when
* differentiating between this method and getAttributeValue.
*/
private AttributeValue getSimpleAttributeValue(final Method getter, final Object getterReturnResult) {
if ( getterReturnResult == null )
return null;
ArgumentMarshaller marshaller = reflector.getArgumentMarshaller(getter);
return marshaller.marshall(getterReturnResult);
}
/**
* Saves the object given into DynamoDB, using the default configuration.
*
* @see DynamoDBMapper#save(Object, DynamoDBMapperConfig)
*/
public <T extends Object> void save(T object) {
save(object, config);
}
/**
* Saves an item in DynamoDB. The service method used is determined by the
* {@link DynamoDBMapperConfig#getSaveBehavior()} value, to use either
* {@link AWSDynamoDB#putItem(PutItemRequest)} or
* {@link AWSDynamoDB#updateItem(UpdateItemRequest)}. For updates, a null
* value for an object property will remove it from that item in DynamoDB.
* For puts, a null value will not be passed to the service. The effect is
* therefore the same, except when the item in DynamoDB contains attributes
* that aren't modeled by the domain object given.
*
* @param object
* The object to save into DynamoDB
* @param config
* The configuration to use, which overrides the default provided
* at object construction.
*/
public <T extends Object> void save(T object, DynamoDBMapperConfig config) {
if ( config != this.config )
config = new DynamoDBMapperConfig(this.config, config);
@SuppressWarnings("unchecked")
Class<? extends T> clazz = (Class<? extends T>) object.getClass();
String tableName = getTableName(clazz, config);
Method hashKeyGetter = reflector.getHashKeyGetter(clazz);
AttributeValue hashKeyElement = getHashKeyElement(safeInvoke(hashKeyGetter, object), hashKeyGetter);
AttributeValue rangeKeyElement = null;
Method rangeKeyGetter = reflector.getRangeKeyGetter(clazz);
if ( rangeKeyGetter != null ) {
rangeKeyElement = getRangeKeyElement(safeInvoke(rangeKeyGetter, object), rangeKeyGetter);
}
Key objectKey = new Key().withHashKeyElement(hashKeyElement).withRangeKeyElement(rangeKeyElement);
Map<String, AttributeValueUpdate> updateValues = new HashMap<String, AttributeValueUpdate>();
Map<String, ExpectedAttributeValue> expectedValues = new HashMap<String, ExpectedAttributeValue>();
// Look at every getter and construct an update object for it
boolean forcePut = false;
List<ValueUpdate> inMemoryUpdates = new LinkedList<DynamoDBMapper.ValueUpdate>();
for ( Method method : reflector.getRelevantGetters(clazz) ) {
Object getterResult = safeInvoke(method, object);
String attributeName = reflector.getAttributeName(method);
/*
* If this is a versioned field, update it
*/
if ( reflector.isVersionAttributeGetter(method) ) {
if ( config.getSaveBehavior() != SaveBehavior.CLOBBER ) {
// First establish the expected (current) value for the
// update call
ExpectedAttributeValue expected = new ExpectedAttributeValue();
// For new objects, insist that the value doesn't exist.
// For existing ones, insist it has the old value.
AttributeValue currentValue = getSimpleAttributeValue(method, getterResult);
expected.setExists(currentValue != null);
if ( currentValue != null ) {
expected.setValue(currentValue);
}
expectedValues.put(attributeName, expected);
}
AttributeValue newVersionValue = getVersionAttributeValue(method, getterResult);
updateValues
.put(attributeName, new AttributeValueUpdate().withAction("PUT").withValue(newVersionValue));
inMemoryUpdates.add(new ValueUpdate(method, newVersionValue));
}
/*
* If this is a new item being saved, assign a key if possible and
* force a put, rather than an update
*/
else if ( getterResult == null && reflector.isAssignableKey(method) ) {
forcePut = true;
AttributeValue newVersionValue = getAutoGeneratedKeyAttributeValue(method, getterResult);
updateValues
.put(attributeName, new AttributeValueUpdate().withAction("PUT").withValue(newVersionValue));
inMemoryUpdates.add(new ValueUpdate(method, newVersionValue));
}
/*
* Otherwise apply the put value for this attribute. Hash and range
* keys are included in puts, but not updates.
*/
else if ( config.getSaveBehavior() == SaveBehavior.CLOBBER
|| (!method.equals(hashKeyGetter) && !method.equals(rangeKeyGetter)) ) {
AttributeValue currentValue = getSimpleAttributeValue(method, getterResult);
if ( currentValue != null ) {
updateValues.put(attributeName, new AttributeValueUpdate().withValue(currentValue)
.withAction("PUT"));
} else if ( config.getSaveBehavior() != SaveBehavior.CLOBBER ) {
updateValues.put(attributeName, new AttributeValueUpdate().withAction("DELETE"));
}
}
}
/*
* Do a put or an update, according to the configuration. For a put (not
* the default), we need to munge the data type.
*/
if ( config.getSaveBehavior() == SaveBehavior.CLOBBER || forcePut ) {
db.putItem(applyUserAgent(new PutItemRequest().withTableName(tableName).withItem(convertToItem(updateValues))
.withExpected(expectedValues)));
} else {
db.updateItem(applyUserAgent(new UpdateItemRequest().withTableName(tableName).withKey(objectKey)
.withAttributeUpdates(updateValues).withExpected(expectedValues)));
}
/*
* Finally, after the service call has succeeded, update the in-memory
* object with new field values as appropriate.
*/
for ( ValueUpdate update : inMemoryUpdates ) {
setValue(object, update.method, update.newValue);
}
}
/**
* Deletes the given object from its DynamoDB table.
*/
public void delete(Object object) {
delete(object, this.config);
}
/**
* Deletes the given object from its DynamoDB table.
*
* @param config
* Config override object. If {@link SaveBehavior#CLOBBER} is
* supplied, version fields will not be considered when deleting
* the object.
*/
public void delete(Object object, DynamoDBMapperConfig config) {
if ( this.config != config )
config = new DynamoDBMapperConfig(this.config, config);
Class<?> clazz = object.getClass();
String tableName = getTableName(clazz, config);
Method hashKeyGetter = reflector.getHashKeyGetter(clazz);
AttributeValue hashKeyElement = getHashKeyElement(safeInvoke(hashKeyGetter, object), hashKeyGetter);
AttributeValue rangeKeyElement = null;
Method rangeKeyGetter = reflector.getRangeKeyGetter(clazz);
if ( rangeKeyGetter != null ) {
rangeKeyElement = getRangeKeyElement(safeInvoke(rangeKeyGetter, object), rangeKeyGetter);
}
Key objectKey = new Key().withHashKeyElement(hashKeyElement).withRangeKeyElement(rangeKeyElement);
/*
* If there is a version field, make sure we assert its value. If the
* version field is null (only should happen in unusual circumstances),
* pretend it doesn't have a version field after all.
*/
Map<String, ExpectedAttributeValue> expectedValues = new HashMap<String, ExpectedAttributeValue>();
if ( config.getSaveBehavior() != SaveBehavior.CLOBBER ) {
for ( Method method : reflector.getRelevantGetters(clazz) ) {
if ( reflector.isVersionAttributeGetter(method) ) {
Object getterResult = safeInvoke(method, object);
String attributeName = reflector.getAttributeName(method);
ExpectedAttributeValue expected = new ExpectedAttributeValue();
AttributeValue currentValue = getSimpleAttributeValue(method, getterResult);
expected.setExists(currentValue != null);
if ( currentValue != null )
expected.setValue(currentValue);
expectedValues.put(attributeName, expected);
break;
}
}
}
db.deleteItem(applyUserAgent(new DeleteItemRequest().withKey(objectKey).withTableName(tableName).withExpected(expectedValues)));
}
/**
* Swallows the checked exceptions around Method.invoke and repackages them
* as {@link DynamoDBMappingException}
*/
private Object safeInvoke(Method method, Object object, Object... arguments) {
try {
return method.invoke(object, arguments);
} catch ( IllegalAccessException e ) {
throw new DynamoDBMappingException("Couldn't invoke " + method, e);
} catch ( IllegalArgumentException e ) {
throw new DynamoDBMappingException("Couldn't invoke " + method, e);
} catch ( InvocationTargetException e ) {
throw new DynamoDBMappingException("Couldn't invoke " + method, e);
}
}
private static final class ValueUpdate {
private Method method;
private AttributeValue newValue;
public ValueUpdate(Method method, AttributeValue newValue) {
this.method = method;
this.newValue = newValue;
}
}
/**
* Converts the {@link AttributeValueUpdate} map given to an equivalent
* {@link AttributeValue} map.
*/
private Map<String, AttributeValue> convertToItem(Map<String, AttributeValueUpdate> putValues) {
Map<String, AttributeValue> map = new HashMap<String, AttributeValue>();
for ( Entry<String, AttributeValueUpdate> entry : putValues.entrySet() ) {
/*
* AttributeValueUpdate allows nulls for its values, since they are
* semantically meaningful. AttributeValues never have null values.
*/
if ( entry.getValue().getValue() != null )
map.put(entry.getKey(), entry.getValue().getValue());
}
return map;
}
/**
* Gets the attribute value object corresponding to the
* {@link DynamoDBVersionAttribute} getter, and its result, given. Null
* values are assumed to be new objects and given the smallest possible
* positive value. Non-null values are incremented from their current value.
*/
private AttributeValue getVersionAttributeValue(final Method getter, Object getterReturnResult) {
ArgumentMarshaller marshaller = reflector.getVersionedArgumentMarshaller(getter, getterReturnResult);
return marshaller.marshall(getterReturnResult);
}
/**
* Returns an attribute value corresponding to the key method and value given.
*/
private AttributeValue getAutoGeneratedKeyAttributeValue(Method getter, Object getterResult) {
ArgumentMarshaller marshaller = reflector.getAutoGeneratedKeyArgumentMarshaller(getter);
return marshaller.marshall(getterResult);
}
/**
* Scans through an AWS DynamoDB table and returns the matching results as
* an unmodifiable list of instantiated objects. The table to scan is
* determined by looking at the annotations on the specified class, which
* declares where to store the object data in AWS DynamoDB, and the scan
* expression parameter allows the caller to filter results and control how
* the scan is executed.
* <p>
* Callers should be aware that the returned list is unmodifiable, and any
* attempts to modify the list will result in an
* UnsupportedOperationException.
*
* @param <T>
* The type of the objects being returned.
*
* @param clazz
* The class annotated with DynamoDB annotations describing how
* to store the object data in AWS DynamoDB.
* @param scanExpression
* Details on how to run the scan, including any filters to apply
* to limit results.
*
* @return An unmodifiable list of the objects constructed from the results
* of the scan operation.
*
* @throws Exception
* If there were any problems loading the data from AWS
* DynamoDB.
*/
public <T> List<T> scan(Class<T> clazz, DynamoDBScanExpression scanExpression) throws Exception {
ScanRequest scanRequest = createScanRequestFromExpression(clazz, scanExpression);
ScanResult scanResult = db.scan(applyUserAgent(scanRequest));
int count = scanResult.getCount();
// If the results are truncated, figure out the count
if (scanResult.getLastEvaluatedKey() != null) {
count = count(clazz, scanExpression);
}
return new PaginatedScanList<T>(this, clazz, db, count, scanRequest, scanResult);
}
/**
* Queries an AWS DynamoDB table and returns the matching results as an
* unmodifiable list of instantiated objects. The table to query is
* determined by looking at the annotations on the specified class, which
* declares where to store the object data in AWS DynamoDB, and the query
* expression parameter allows the caller to filter results and control how
* the query is executed.
* <p>
* Callers should be aware that the returned list is unmodifiable, and any
* attempts to modify the list will result in an
* UnsupportedOperationException.
*
* @param <T>
* The type of the objects being returned.
*
* @param clazz
* The class annotated with DynamoDB annotations describing how
* to store the object data in AWS DynamoDB.
* @param queryExpression
* Details on how to run the query, including any filters to
* apply to limit the results.
*
* @return An unmodifiable list of the objects constructed from the results
* of the query operation.
*
* @throws Exception
* If there were any problems loading the data from AWS
* DynamoDB.
*/
public <T> List<T> query(Class<T> clazz, DynamoDBQueryExpression queryExpression) throws Exception {
QueryRequest queryRequest = createQueryRequestFromExpression(clazz, queryExpression);
QueryResult queryResult = db.query(applyUserAgent(queryRequest));
int count = queryResult.getCount();
// If the results are truncated, figure out the count
if (queryResult.getLastEvaluatedKey() != null) {
count = count(clazz, queryExpression);
}
return new PaginatedQueryList<T>(this, clazz, db, count, queryRequest, queryResult);
}
/**
* Evaluates the specified scan expression and returns the count of matching
* items, without returning any of the actual item data.
*
* @param clazz
* The class mapped to a DynamoDB table.
* @param scanExpression
* The parameters for running the scan.
*
* @return The count of matching items, without returning any of the actual
* item data.
*
* @throws Exception
* If any problems were encountered making the request to AWS
* DynamoDB.
*/
public int count(Class<?> clazz, DynamoDBScanExpression scanExpression) throws Exception {
ScanRequest scanRequest = createScanRequestFromExpression(clazz, scanExpression);
scanRequest.setCount(true);
// Count scans can also be truncated for large datasets
int count = 0;
ScanResult scanResult = null;
do {
scanResult = db.scan(applyUserAgent(scanRequest));
count += scanResult.getCount();
scanRequest.setExclusiveStartKey(scanResult.getLastEvaluatedKey());
} while (scanResult.getLastEvaluatedKey() != null);
return count;
}
public int count(Class<?> clazz, DynamoDBQueryExpression queryExpression) throws Exception {
QueryRequest queryRequest = createQueryRequestFromExpression(clazz, queryExpression);
queryRequest.setCount(true);
// Count queries can also be truncated for large datasets
int count = 0;
QueryResult queryResult = null;
do {
queryResult = db.query(applyUserAgent(queryRequest));
count += queryResult.getCount();
queryRequest.setExclusiveStartKey(queryResult.getLastEvaluatedKey());
} while (queryResult.getLastEvaluatedKey() != null);
return count;
}
private ScanRequest createScanRequestFromExpression(Class<?> clazz, DynamoDBScanExpression scanExpression) {
DynamoDBTable table = reflector.getTable(clazz);
ScanRequest scanRequest = new ScanRequest();
scanRequest.setTableName(table.tableName());
scanRequest.setScanFilter(scanExpression.getScanFilter());
return scanRequest;
}
private QueryRequest createQueryRequestFromExpression(Class<?> clazz, DynamoDBQueryExpression queryExpression) {
DynamoDBTable table = reflector.getTable(clazz);
QueryRequest queryRequest = new QueryRequest();
queryRequest.setConsistentRead(queryExpression.isConsistentRead());
queryRequest.setTableName(table.tableName());
queryRequest.setHashKeyValue(queryExpression.getHashKeyValue());
queryRequest.setScanIndexForward(queryExpression.isScanIndexForward());
queryRequest.setRangeKeyCondition(queryExpression.getRangeKeyCondition());
return queryRequest;
}
static <X extends AmazonWebServiceRequest> X applyUserAgent(X request) {
request.getRequestClientOptions().addClientMarker(USER_AGENT);
return request;
}
}