查询某类产品

Question

我在 DynamoDb 中有一个简单的“products”表。每个产品都有一个categories 属性，它是一组类别 ID，如下所示：

[{ "N" : "4" },{ "N" : "5" },{ "N" : "6" },{ "N" : "8" }]

products 表有id（哈希键）和accountId（范围键）

是否可以进行查询以查找属于类别 6 和 accountId 1 的所有产品无需进行扫描？或者我可以通过其他方式对此进行建模吗？

如果它是一个关系数据库，我将有一个产品到类别表，并加入产品。如果我在 Dynamo 中有一个类似的表，那么我需要为产品表中的每个产品创建一个 GetItem，这感觉是个坏主意？

Answer 1

根据您的描述，听起来最好的解决方法是使用GSI。

您的表格结构如下：

• 哈希键：id
• 范围键：accountId
• 属性-categories

您将创建一个具有此结构的全局二级索引：

• 哈希键：accountId
• 范围键：id
• 属性-categories

然后您就可以使用您提到的条件查询该索引：

1. accountId = 1
2. categories contains 6

这是我针对 DynamoDB local 编写的一个快速示例，它将所有属性投影到索引上。

import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClient;
import com.amazonaws.services.dynamodbv2.document.DynamoDB;
import com.amazonaws.services.dynamodbv2.document.Index;
import com.amazonaws.services.dynamodbv2.document.Item;
import com.amazonaws.services.dynamodbv2.document.QueryFilter;
import com.amazonaws.services.dynamodbv2.document.Table;
import com.amazonaws.services.dynamodbv2.document.spec.QuerySpec;
import com.amazonaws.services.dynamodbv2.model.AttributeDefinition;
import com.amazonaws.services.dynamodbv2.model.CreateTableRequest;
import com.amazonaws.services.dynamodbv2.model.GlobalSecondaryIndex;
import com.amazonaws.services.dynamodbv2.model.KeySchemaElement;
import com.amazonaws.services.dynamodbv2.model.KeyType;
import com.amazonaws.services.dynamodbv2.model.Projection;
import com.amazonaws.services.dynamodbv2.model.ProjectionType;
import com.amazonaws.services.dynamodbv2.model.ProvisionedThroughput;
import com.amazonaws.services.dynamodbv2.model.ScalarAttributeType;
import com.amazonaws.services.dynamodbv2.util.Tables;
public class StackOverflow {

    private static final String EXAMPLE_TABLE_NAME = "example_table";
    private static final String HASH_KEY = "id";
    private static final String RANGE_KEY = "accountId";
    private static final String GSI = "accountIdToId";
    private static final String CATEGORIES = "categories";

    public static void main(String[] args) throws InterruptedException {
        AmazonDynamoDB
            client =
            new AmazonDynamoDBClient(new BasicAWSCredentials("accessKey", "secretKey"));
        client.setEndpoint("http://localhost:4000");
        DynamoDB dynamoDB = new DynamoDB(client);
        if (Tables.doesTableExist(client, EXAMPLE_TABLE_NAME)) {
            client.deleteTable(EXAMPLE_TABLE_NAME);
        }

        CreateTableRequest createTableRequest = new CreateTableRequest();
        createTableRequest.withTableName(EXAMPLE_TABLE_NAME);
        createTableRequest.withKeySchema(new KeySchemaElement(HASH_KEY, KeyType.HASH),
                                         new KeySchemaElement(RANGE_KEY, KeyType.RANGE));
        createTableRequest.withAttributeDefinitions(
            new AttributeDefinition(HASH_KEY, ScalarAttributeType.S),
            new AttributeDefinition(RANGE_KEY, ScalarAttributeType.S));
        createTableRequest.withProvisionedThroughput(new ProvisionedThroughput(15l, 15l));
        // GSI definition
        final GlobalSecondaryIndex
            accountIdToId =
            new GlobalSecondaryIndex().withIndexName(GSI).withKeySchema(
                new KeySchemaElement(RANGE_KEY, KeyType.HASH),
                new KeySchemaElement(HASH_KEY, KeyType.RANGE)).withProvisionedThroughput(
                new ProvisionedThroughput(10l, 10l)).withProjection(
                new Projection().withProjectionType(ProjectionType.ALL));
        createTableRequest.withGlobalSecondaryIndexes(accountIdToId);

        final Table table = dynamoDB.createTable(createTableRequest);
        table.waitForActive();

        table.putItem(new Item()
                          .withPrimaryKey(HASH_KEY, "1", RANGE_KEY, "6")
                          .withNumberSet(CATEGORIES, 1, 2, 5, 6));

        table.putItem(new Item()
                                 .withPrimaryKey(HASH_KEY, "2", RANGE_KEY, "6")
                                 .withNumberSet(CATEGORIES, 5, 6));

        table.putItem(new Item()
                                 .withPrimaryKey(HASH_KEY, "5", RANGE_KEY, "6")
                                 .withNumberSet(CATEGORIES, 1, 2));

        table.putItem(new Item()
                                 .withPrimaryKey(HASH_KEY, "5", RANGE_KEY, "8")
                                 .withNumberSet(CATEGORIES, 1, 2, 6));

        System.out.println("Scan the table, no filters");
        table.scan().forEach(System.out::println);
        System.out.println();

        final Index gsi = table.getIndex(GSI);

        System.out.println("Scan the GSI without filter");
        gsi.scan().forEach(System.out::println);
        System.out.println();
        System.out.println("Query the GSI with range key condition and contains");

        final QuerySpec querySpec = new QuerySpec()
            .withHashKey(RANGE_KEY, "6")
            .withQueryFilters(new QueryFilter(CATEGORIES).contains(6));
        gsi.query(querySpec).forEach(System.out::println);
        System.out.println();
    }
}

输出：

Scan the table, no filters
{ Item: {accountId=6, id=1, categories=[1, 2, 5, 6]} }
{ Item: {accountId=6, id=5, categories=[1, 2]} }
{ Item: {accountId=8, id=5, categories=[1, 2, 6]} }
{ Item: {accountId=6, id=2, categories=[5, 6]} }

Scan the GSI without filter
{ Item: {accountId=6, id=1, categories=[1, 2, 5, 6]} }
{ Item: {accountId=6, id=5, categories=[1, 2]} }
{ Item: {accountId=8, id=5, categories=[1, 2, 6]} }
{ Item: {accountId=6, id=2, categories=[5, 6]} }

Query the GSI with range key condition and contains
{ Item: {accountId=6, id=1, categories=[1, 2, 5, 6]} }
{ Item: {accountId=6, id=2, categories=[5, 6]} }

Answer 2

创建另一个表，并在更新主表时对其进行更新。真的，无论如何，这就是在 RDBMS 中发生的事情，只是它在后台。当亚马逊为表设置二级索引时，它们基本上只是自动化了人们一直在做的事情。