Question

我正在尝试从AWS DynamoDB数据库中获取数据。我设置了以下代码，但是我遇到了错误。不清楚如何从这里开始以便基于主键查询数据

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);

Answer 1

首先评论一下，看起来你在一个Activity中尝试这个 - 这肯定会在Android中引发网络主线程异常。

其次，作为一般指南，您需要设置一个单独的类，其中DynamoDB字段已设置并链接到类中的变量。例如：

@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;
    }
}

然后你可以这样做：

                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);
                }

您必须注意AWS使用单个查询设置的数据返回限制（因此PaginatedScan - 如果您希望超出限制，则需要检查是否存在更多数据要返回）。 / p>

从AWS DynamoDB for Android查询

1 个答案: