Conditional update in Dynamo Db using mapper

Question

I am trying to do a conditional update on a field Score in my table based on the condition that marks to be updated are greater than the current score.

I have written following code ,

StudentDO temp = mapper.load(StudentDO.class, student.getId());
temp.setScore(marks);
ArrayList<AttributeValue> list = new ArrayList<AttributeValue>();
            list.add(new AttributeValue().withN(Oldmarks.toString()));

            Map<String,ExpectedAttributeValue> expectedAttributes = new 
                                                                                                                   HashMap<String,ExpectedAttributeValue>();

            ExpectedAttributeValue expectedAttributeValue = new 
                                                                                                     ExpectedAttributeValue().withAttributeValueList(list)
                                                                                                                                       .withComparisonOperator("GT");

            expectedAttributes.put("Score",expectedAttributeValue);
            mapper.save(temp, new DynamoDBSaveExpression().withExpected(expectedAttributes));

This is failing with this runtime exception

com.amazonaws.services.dynamodbv2.model.ConditionalCheckFailedException: The conditional request failed (Service: null; Status Code: 400; Error Code: ConditionalCheckFailedException; Request ID: null)

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.amazonaws.services.dynamodbv2.local.embedded.DDBExceptionMappingInvocationHandler.handleDynamoDBLocalServiceException(DDBExceptionMappingInvocationHandler.java:87)
at com.amazonaws.services.dynamodbv2.local.embedded.DDBExceptionMappingInvocationHandler.invoke(DDBExceptionMappingInvocationHandler.java:66)
at com.sun.proxy.$Proxy19.updateItem(Unknown Source)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper$SaveObjectHandler.doUpdateItem(DynamoDBMapper.java:854)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper$2.executeLowLevelRequest(DynamoDBMapper.java:594)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper$SaveObjectHandler.execute(DynamoDBMapper.java:733)
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.save(DynamoDBMapper.java:623)
at com.amazonaws.services.dynamodbv2.datamodeling.AbstractDynamoDBMapper.save(AbstractDynamoDBMapper.java:128)

I am not able to debug why is it throwing Conditional Check Failed Exception. I could make out the request is not properly formed , but not sure where is it malformed ?

I have tried to align it to these docs http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/dynamodbv2/datamodeling/DynamoDBSaveExpression.html

http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/dynamodbv2/model/ExpectedAttributeValue.html

http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/dynamodbv2/model/AttributeValue.html

My DB schema is this

@DynamoDBTable(tableName = "Student")

public class StudentDO {
    @DynamoDBHashKey(attributeName = "Id")
    private Integer id;

    @DynamoDBAttribute(attributeName = "Name")
    private String name;

    @DynamoDBAttribute(attributeName = "Score")
    private Integer score;

    @Override
    public String toString() {

        return "Student [Name=" + name + ", id=" + id + ", score=" + score + "]";
    }


}

davidchuyaya davidchuyaya · Accepted Answer · 2019-06-24T17:24:45

Each DynamoDB attribute must have a public getter and setter, since DynamoDBMapper works on JavaBeans (a class with a no argument constructor, and getters + setters for each private var). Modify your class to this:

@DynamoDBTable(tableName = "Student")
public class StudentDO {
    private Integer id;
    private String name;
    private Integer score;

    @DynamoDBAttribute(attributeName = "Id")
    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    @DynamoDBAttribute(attributeName = "Name")
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @DynamoDBAttribute(attributeName = "Score")
    public Integer getScore() {
        return score;
    }

    public void setScore(Integer score) {
        this.score = score;
    }

    @Override
    public String toString() {

        return "Student [Name=" + name + ", id=" + id + ", score=" + score + "]";

    }
}

Conditional update in Dynamo Db using mapper

1 Answers