在不使用扫描的情况下验证DynamoDB中的属性？

问题描述

如何在不使用dynamodb中使用scan的情况下验证属性是否存在于表中？

How to verify an attribute whether it present in table or not without using scan in dynamodb?

在我的用例中，来自客户端的客户请求及其Customer_id了解产品的价值。在服务器端，必须检查输入的customer_id是否已存在于DynamoDB表中。如果没有，则必须重新输入。

In my usecase, From client side, The customer request with their Customer_id for knowing the values of the product. In server side, have to check whether the entered customer_id already present in DynamoDB table or not. If not, have to make a new entry.

如何在不对表使用SCAN操作的情况下实现这种情况？

How can I implement this case without using SCAN operation to the table?

推荐答案

在我看来，您要在此表上执行条件 PutItem ：如果没有另一个具有相同<$的项目，则将该项目放入表中c $ c> customer_id 。这很容易做到，因为 customer_id 是表的哈希键。从 PutItem ：

It sounds to me that you want to do a conditional PutItem on this table: put the item into the table if there is not another item with the same customer_id. This is easy enough to do because the customer_id is the hash key of the table. From the PutItem documentation:

为防止新项目替换现有项目，请对
主键属性使用条件放置操作，将 ComparisonOperator 设置为 NULL ，或属性。

To prevent a new item from replacing an existing item, use a conditional put operation with ComparisonOperator set to NULL for the primary key attribute, or attributes.

这里是一个简单的示例，我使用Java SDK中的Dynamo DB文档API编写了代码，并针对DynamoDB Local运行：

Here is a quick example I coded up using the Dynamo DB document API in the Java SDK and running against DynamoDB Local:

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.Expected;
import com.amazonaws.services.dynamodbv2.document.Item;
import com.amazonaws.services.dynamodbv2.document.Table;
import com.amazonaws.services.dynamodbv2.model.AttributeDefinition;
import com.amazonaws.services.dynamodbv2.model.ConditionalCheckFailedException;
import com.amazonaws.services.dynamodbv2.model.CreateTableRequest;
import com.amazonaws.services.dynamodbv2.model.KeySchemaElement;
import com.amazonaws.services.dynamodbv2.model.KeyType;
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";

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

        // Create table with hash key 'customer_id'
        CreateTableRequest createTableRequest = new CreateTableRequest();
        createTableRequest.withTableName(EXAMPLE_TABLE_NAME);
        createTableRequest.withKeySchema(new KeySchemaElement("customer_id", KeyType.HASH));
        createTableRequest.withAttributeDefinitions(new AttributeDefinition("customer_id", ScalarAttributeType.S));
        createTableRequest.withProvisionedThroughput(new ProvisionedThroughput(15l, 15l));
        dynamoDB.createTable(createTableRequest);
        Tables.waitForTableToBecomeActive(client, EXAMPLE_TABLE_NAME);

        Table exampleTable = dynamoDB.getTable(EXAMPLE_TABLE_NAME);

        exampleTable.putItem(new Item()
                .withPrimaryKey("customer_id", "ABCD")
                .withString("customer_name", "Jim")
                .withString("customer_email", "[email protected]"));

        System.out.println("After Jim:");
        exampleTable.scan()
                    .forEach(System.out::println);
        System.out.println();

        try {
            exampleTable.putItem(new Item()
                    .withPrimaryKey("customer_id", "EFGH")
                    .withString("customer_name", "Garret")
                    .withString("customer_email", "[email protected]"), new Expected("customer_id").notExist());
        } catch (ConditionalCheckFailedException e) {
            System.out.println("Conditional check failed!");
        }

        System.out.println("After Garret:");
        exampleTable.scan()
                    .forEach(System.out::println);
        System.out.println();

        try {
            exampleTable.putItem(new Item()
                    .withPrimaryKey("customer_id", "ABCD")
                    .withString("customer_name", "Bob")
                    .withString("customer_email", "[email protected]"), new Expected("customer_id").notExist());
        } catch (ConditionalCheckFailedException e) {
            System.out.println("Conditional check failed!");
        }

        System.out.println("After Bob:");
        exampleTable.scan()
                    .forEach(System.out::println);
    }
}

输出：

After Jim:
{ Item: {[email protected], customer_name=Jim, customer_id=ABCD} }

After Garret:
{ Item: {[email protected], customer_name=Garret, customer_id=EFGH} }
{ Item: {[email protected], customer_name=Jim, customer_id=ABCD} }

Conditional check failed!
After Bob:
{ Item: {[email protected], customer_name=Garret, customer_id=EFGH} }
{ Item: {[email protected], customer_name=Jim, customer_id=ABCD} }

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