java - 无法将多个对象保存到 DynamoDB？

Question

我试图通过一项服务将多个条目添加到我的 DynamoDB 数据库中，但是在执行代码时，只保存了一个条目。这是我到目前为止所做的:

public int onStartCommand(Intent intent, int flags, int startId) {

    CognitoCachingCredentialsProvider credentialsProvider = new CognitoCachingCredentialsProvider(
            getApplicationContext(), // Context
            "us-east-1:851c121e-326d-4c9e-be47-fec40eb7b693", // Identity Pool ID
            Regions.US_EAST_1 // Region
    );

    AmazonDynamoDB client = new AmazonDynamoDBClient(credentialsProvider);

    Toast.makeText(this, "Adding To Database...", Toast.LENGTH_LONG).show();

    CognitoCachingCredentialsProvider cognitoProvider = new CognitoCachingCredentialsProvider(
            getApplicationContext(), // Context
            "us-east-1:851c121e-326d-4c9e-be47-fec40eb7b693", // Identity Pool ID
            Regions.US_EAST_1 // Region
    );

    AmazonDynamoDBClient ddbClient = new AmazonDynamoDBClient(cognitoProvider);

    DynamoDBMapper mapper = new DynamoDBMapper(ddbClient);

    String streamName = intent.getStringExtra("streamName");
    String userCreated = intent.getStringExtra("userCreated");
    ArrayList<String> selectedFriend = intent.getStringArrayListExtra("userInvolved");
    intent.getStringExtra("comment");

    for(int i = 0; i < selectedFriend.size(); i++){

        Streams streams = new Streams();

        streams.setStreamname(streamName);
        streams.setUsercreated(userCreated);
        streams.setUserinvolved(selectedFriend.get(i));
        streams.setUnread(true);
        streams.setDeleted(false);

        mapper.save(streams);

    }
}

就像我说的，只会保存一个条目。有人建议我使用数组列表，但我不确定该怎么做。谁能帮忙？

感谢所有帮助。

编辑:Streams.java 类:

@DynamoDBTable(tableName = "Streams")
public class Streams{

    private String streamname;
    private String usercreated;
    private String userinvolved;
    private boolean unread;
    private boolean deleted;

    @DynamoDBAttribute(attributeName = "Stream_Name")
    public String getStreamname() {
        return streamname;
    }

    public void setStreamname(String streamname) {
        this.streamname = streamname;
    }

    @DynamoDBHashKey(attributeName = "User_Created")
    public String getUsercreated() {
        return usercreated;
    }

    public void setUsercreated(String usercreated) {
        this.usercreated = usercreated;
    }

    @DynamoDBAttribute(attributeName = "User_Involved")
    public String getUserinvolved() {
        return userinvolved;
    }

    public void setUserinvolved(String userinvolved) {
        this.userinvolved = userinvolved;
    }

    @DynamoDBAttribute(attributeName = "Unread")
    public boolean isUnread() {
        return unread;
    }

    public void setUnread(boolean unread) {
        this.unread = unread;
    }

    @DynamoDBAttribute(attributeName = "Deleted")
    public boolean isDeleted() {
        return deleted;
    }

    public void setDeleted(boolean deleted) {
        this.deleted = deleted;
    }
}

Answer 1

您的 DynamoDB 哈希键似乎是 Stream 类中的 user created 字段。这是 DynamoDB 主键，它唯一标识 DynamoDB 表中的单个项目。

每次您调用 mapper.save(streams) 时，您都会覆盖您在循环的前一次迭代中编写的项目，因为您似乎只设置了 user created 字段一次在这里:

String userCreated = intent.getStringExtra("userCreated");。

尝试使用唯一标识符(例如 stream name 作为哈希键)。如果多个项目具有相同的哈希键，您还可以使用具有范围键的架构来创建(哈希键、范围键)主键以唯一标识 DynamoDB 表中的项目。