如何基于分区键和排序键[Java]查询DynamoDB？

我是DynamoDB新手，想知道如何使用hashKey和sortKey在DynamoDB中查询表

我有一个名为

Items

的表。它的模式是

1. Product (Partition Key of type String)
2. ID (Sort Key of type int)
3. Date ( attribute of type String)

获取所有具有

product=10

的项目的查询是

Items it = new Items();
it.setProduct("apple");

DynamoDBQueryExpression<Items> queryExpression = new DynamoDBQueryExpression<Items>()
            .withHashKeyValues(it);


List<Items> itemList = mapper.query(Items.class, queryExpression);

Items it=newitems（）；
it.setProduct（“苹果”）；
DynamoDBQueryExpression queryExpression=新建DynamoDBQueryExpression（）
.withHashKeyValues（it）；
List itemList=mapper.query（Items.class，queryExpression）；

但是，现在我想获得所有具有

Product=“apple”

和

ID=100

的项目

---

我可以在

Java

中为

DynamoDB

编写一个查询

以便使用分区键和排序键从DynamoDB获取数据。您可以使用

DynamoDBMapper

类中的

load

方法

DynamoDBMapper mapper = new DynamoDBMapper(dynamoDBClient);
String product = "ball";
Integer id = 1;
Item itemObj = mapper.load(Items.class, product, id);

模型类，即您的案例中的项目类：-

您应该使用哈希和范围键的适当注释定义Item类

@DynamoDBTable(tableName = "Items")
public class Item {

    private String product;
    private Integer id;

    @DynamoDBHashKey(attributeName = "Product")
    public String getProduct() {
        return autoID;
    }   
    @DynamoDBRangeKey(attributeName = "ID")
    public String getId() {
        return id;
    }           
}   

---

我想添加一种更低级的方法（不使用映射器和注释）：

String accessKey=…；//不要在生产中硬编码密钥。
字符串secretKey=。。。；
AmazonDynamoDB Dynamodb客户端=
=AmazondynamodClientBuilder
.standard（）
.withRegion（“us-east-1”）
.具有凭据（新的AWSStaticCredentialsProvider（新的基本凭据（accessKey、secretKey）））
.build（）；
字符串tableName=。。。
Map.Entry partitionKey=。。。
Map.Entry sortKey=。。。
GetItemRequest请求=
新建GetItemRequest（）.withTableName（tableName）
.withKey（分区键、排序键）；
GetItemResult=dynamoDBClient.getItem（请求）；
Map item=result.getItem（）；

GetItemRequest GetItemRequest=new GetItemRequest（）.withTableName（“员工”）。
addKeyEntry（“departmentId”，新的AttributeValue（）.with（String.valueOf（departmentId）））。
addKeyEntry（“employeeId”，新的AttributeValue（）.withN（String.valueOf（employeeId）））；
Map responseItem=dynamoDbClient.getItem（getItemRequest.getItem（）；

给定此发电机表：

该表包含以下详细信息：

• 分区键艺术家
• 排序键-歌曲标题

鉴于这一类别：

@DynamoDBTable(tableName="Music")
public class MusicItems {

    //Set up Data Members that correspond to items in the Music Table
    private String artist;
    private String songTitle;
    private String albumTitle;
    private int awards;

    @DynamoDBHashKey(attributeName="Artist")
    public String getArtist() { return this.artist; }
    public void setArtist(String artist) {this.artist = artist; }

    @DynamoDBRangeKey(attributeName="SongTitle")
    public String getSongTitle() { return this.songTitle; }
    public void setSongTitle(String title) {this.songTitle = title; }

    @DynamoDBAttribute(attributeName="AlbumTitle")
    public String getAlbumTitle() { return this.albumTitle; }
    public void setAlbumTitle(String title) {this.albumTitle = title; }

    @DynamoDBAttribute(attributeName="Awards")
    public int getAwards() { return this.awards; }
    public void setAwards(int awards) {this.awards = awards; }



}

此代码适用于：

    import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
    import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
    import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAttribute;
    import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBHashKey;
    import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper;
    import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapperConfig;
    import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTable;

    public class UseDynamoMapping {

    public static void main(String[] args)
    {

       AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();
       MusicItems items = new MusicItems();

       try{

          //add new content to the Music Table
           items.setArtist("Famous Band");
           items.setSongTitle("Our Famous Song");
           items.setAlbumTitle("Our First Album");
           items.setAwards(0);

           // Save the item
           DynamoDBMapper mapper = new DynamoDBMapper(client);
           mapper.save(items);

            //Load an item based on the Partition Key and Sort Key
           //both values need to be passed to the mapper.load method
           String artist = "Famous Band";
           String songQueryTitle = "Our Famous Song";

           // Retrieve the item.
           MusicItems itemRetrieved = mapper.load(MusicItems.class, artist, songQueryTitle);
           System.out.println("Item retrieved:");
           System.out.println(itemRetrieved);

            //Modify the Award value
           itemRetrieved.setAwards(2);
           mapper.save(itemRetrieved);
           System.out.println("Item updated:");
           System.out.println(itemRetrieved);


            System.out.print("Done");
       }
       catch (Exception e)
       {
           e.getStackTrace();
       }

    }
}

---

示例的URL-

我得到一个错误，说，table；没有范围键ID的映射是排序键而不是范围键。已使用模型类更新答案。同样，也可以定义非关键属性。但要使load正常工作，不需要非键属性。如果我想在一个非常大的数据库上运行排序键，它的加载速度和查询速度一样快，这并没有性能。唯一的区别是不能按非关键点属性过滤。查询API有一个功能，可以在筛选条件中包括非关键属性以及关键属性。

@DynamoDBTable(tableName="Music")
public class MusicItems {

    //Set up Data Members that correspond to items in the Music Table
    private String artist;
    private String songTitle;
    private String albumTitle;
    private int awards;

    @DynamoDBHashKey(attributeName="Artist")
    public String getArtist() { return this.artist; }
    public void setArtist(String artist) {this.artist = artist; }

    @DynamoDBRangeKey(attributeName="SongTitle")
    public String getSongTitle() { return this.songTitle; }
    public void setSongTitle(String title) {this.songTitle = title; }

    @DynamoDBAttribute(attributeName="AlbumTitle")
    public String getAlbumTitle() { return this.albumTitle; }
    public void setAlbumTitle(String title) {this.albumTitle = title; }

    @DynamoDBAttribute(attributeName="Awards")
    public int getAwards() { return this.awards; }
    public void setAwards(int awards) {this.awards = awards; }



}

    import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
    import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
    import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAttribute;
    import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBHashKey;
    import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper;
    import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapperConfig;
    import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTable;

    public class UseDynamoMapping {

    public static void main(String[] args)
    {

       AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();
       MusicItems items = new MusicItems();

       try{

          //add new content to the Music Table
           items.setArtist("Famous Band");
           items.setSongTitle("Our Famous Song");
           items.setAlbumTitle("Our First Album");
           items.setAwards(0);

           // Save the item
           DynamoDBMapper mapper = new DynamoDBMapper(client);
           mapper.save(items);

            //Load an item based on the Partition Key and Sort Key
           //both values need to be passed to the mapper.load method
           String artist = "Famous Band";
           String songQueryTitle = "Our Famous Song";

           // Retrieve the item.
           MusicItems itemRetrieved = mapper.load(MusicItems.class, artist, songQueryTitle);
           System.out.println("Item retrieved:");
           System.out.println(itemRetrieved);

            //Modify the Award value
           itemRetrieved.setAwards(2);
           mapper.save(itemRetrieved);
           System.out.println("Item updated:");
           System.out.println(itemRetrieved);


            System.out.print("Done");
       }
       catch (Exception e)
       {
           e.getStackTrace();
       }

    }
}