如何基于分区键和排序键查询DynamoDB [Java]？

How to query DynamoDB based on Partition Key and Sort Key [Java]?

提问by John Constantine

I am new to DynamoDB and wanted to know how can we query on a table in DynamoDB with the hashKey and sortKey.

我是 DynamoDB 的新手，想知道我们如何使用 hashKey 和 sortKey 查询 DynamoDB 中的表。

I have a table named Items. It`s schema is

我有一张名为Items. 它的架构是

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

My query for getting all items having product = 10is

我获取所有项目的查询product = 10是

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

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


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

But, now I want to get all items having Product = "apple"and ID = 100.

但是，现在我想获得所有具有Product = "apple"和 的项目ID = 100。

I can I write a query in Javafor DynamoDB.

我可以在Javafor 中写一个查询DynamoDB。

回答by notionquest

In order to get the data from DynamoDB using partition key and sort key. You can use the loadmethod present on DynamoDBMapperclass.

为了使用分区键和排序键从 DynamoDB 获取数据。您可以使用课堂load上的方法DynamoDBMapper。

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

Model class i.e. in your case Item class:-

模型类，即在您的情况下 Item 类：-

You should have the Item class defined with proper annotation for Hash and Range key.

您应该使用 Hash 和 Range 键的正确注释定义 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;
    }           
}   

回答by MarcG

I would like to add a more low-level way (not using Mapper and annotations):

我想添加一个更底层的方式（不使用 Mapper 和注释）：

String accessKey = ...; // Don't hardcode keys in production.
String secretKey = ...; 

AmazonDynamoDB dynamoDBClient =
      = AmazonDynamoDBClientBuilder
            .standard()
            .withRegion("us-east-1")
            .withCredentials(new AWSStaticCredentialsProvider(new BasicAWSCredentials(accessKey, secretKey)))
            .build();

String tableName = ...
Map.Entry<String, AttributeValue> partitionKey = ...
Map.Entry<String, AttributeValue> sortKey = ...

GetItemRequest request = 
    new GetItemRequest().withTableName(tableName)
                        .withKey(partitionKey, sortKey);

GetItemResult result = dynamoDBClient.getItem(request);
Map<String, AttributeValue> item = result.getItem();

回答by smac2020

Given this DynamoDB table:

鉴于此 DynamoDB 表：

The table has the following details:

该表具有以下详细信息：

• Partition key — Artist
• Sort key — SongTitle

• 分区键 — 艺术家
• 排序键 — SongTitle

Given this class:

鉴于这个类：

@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; }



}

This code works:

此代码有效：

    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();
       }

    }
}

回答by Vikky

GetItemRequest getItemRequest = new GetItemRequest().withTableName("Employee").
            addKeyEntry("departmentId", new AttributeValue().withS(String.valueOf(departmentId))).
            addKeyEntry("employeeId", new AttributeValue().withN(String.valueOf(employeeId)));

    Map<String, AttributeValue> responseItem = dynamoDbClient.getItem(getItemRequest).getItem();