CODEWITHSUNDEEP
androidamazon-web-servicesamazon-dynamodb
joseph wallberg
joseph wallberg

Reputation: 85

Query from AWS DynamoDB for Android

I am trying to fetch data from my AWS DynamoDB database. I have the following code set up, however I am getting errors. Unclear how to proceed from here in order to query the data based on primary key

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import com.amazonaws.auth.CognitoCachingCredentialsProvider;
import com.amazonaws.regions.Regions;
import com.amazonaws.services.dynamodbv2.*;
import com.amazonaws.mobileconnectors.dynamodbv2.dynamodbmapper.*;

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}

CognitoCachingCredentialsProvider credentialsProvider = new CognitoCachingCredentialsProvider(
        getApplicationContext(),
        "**********************", // Identity Pool ID
        Regions.US_EAST_1 // Region
);

AmazonDynamoDBClient ddbClient = new AmazonDynamoDBClient(credentialsProvider);
DynamoDBMapper mapper = new DynamoDBMapper(ddbClient);

Upvotes: 0

Views: 1733

Answers (1)

heights1976
heights1976

Reputation: 500

First comment, it looks like you are trying to this in an Activity -- this will definitely throw Network on Main Thread exception in Android.

Second, as a general guide, you need to set up a separate class with your DynamoDB fields set up and linked to variables in the class. For example:

@DynamoDBTable(tableName = SA_AWSConstants.QUESTIONTABLENAME)
public class SA_Question implements Comparable<SA_Question> {

    // fields coming from AWS table
    private String questionguid_str; // : STRING, PRIMARY HASH KEY
    private String json_str;
    private long ordinalposition_int;

    ...

    @DynamoDBHashKey(attributeName = SA_AWSConstants.DBSCHEMA_QUESTIONGUID)
    public String getQuestionguid_str() {
        return questionguid_str;
    }

    public void setQuestionguid_str(String questionguid_str) {
        this.questionguid_str = questionguid_str;
    }

    @DynamoDBRangeKey(attributeName = SA_AWSConstants.DBSCHEMA_ORDINALPOS)
    public long getOrdinalposition_int() {
        return ordinalposition_int;
    }

    public void setOrdinalposition_int(long ordinalposition_int) {
        this.ordinalposition_int = ordinalposition_int;
    }

    @DynamoDBAttribute(attributeName = SA_AWSConstants.DBSCHEMA_QUESTION_JSONSTR)
    public String getJson_str() {
        return json_str;
    }

    public void setJson_str(String json_str) {
        this.json_str = json_str;
    }
}

Then you can do something like this:

                DynamoDBMapper mapper = new DynamoDBMapper(ddb);
                DynamoDBScanExpression scanExpression = new DynamoDBScanExpression();

                PaginatedScanList<SA_Question> paginatedq = mapper.scan(SA_Question.class, scanExpression);
                ArrayList<SA_Question> awsqlist = new ArrayList<SA_Question>();

                for (SA_Question q : paginatedq) {
                    q.initiateFromJSON();
                    awsqlist.add(q);
                }

You have to be mindful of the limits AWS sets on returns of data with a single query (hence the PaginatedScan -- if you expect to exceed the limit then you will need to check whether more data exists to be returned).

Upvotes: 1

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