Dynamodb 简明教程

DynamoDB - Update Items

在 DynamoDB 中更新一个项目主要包括为项目指定完整的主键和表名。您需要修改的每个属性都需要一个新值。该操作使用 UpdateItem ，它修改现有项目或在发现缺少项目时创建它们。

Updating an item in DynamoDB mainly consists of specifying the full primary key and table name for the item. It requires a new value for each attribute you modify. The operation uses UpdateItem, which modifies the existing items or creates them on discovery of a missing item.

更新中，您可能希望通过在操作之前和之后显示原始值和新值来跟踪更改。UpdateItem 使用 ReturnValues 参数来实现此目的。

In updates, you might want to track the changes by displaying the original and new values, before and after the operations. UpdateItem uses the ReturnValues parameter to achieve this.

Note − 该操作不报告预留单元消耗，但您可以使用 ReturnConsumedCapacity 参数。

Note − The operation does not report capacity unit consumption, but you can use the ReturnConsumedCapacity parameter.

使用 GUI 控制台、Java 或任何其他工具执行此任务。

Use the GUI console, Java, or any other tool to perform this task.

How to Update Items Using GUI Tools?

导航到控制台。在左侧的导航窗格中，选择 Tables 。选择所需的表，然后选择 Items 选项卡。

Navigate to the console. In the navigation pane on the left side, select Tables. Choose the table needed, and then select the Items tab.

选择希望更新的项目，然后选择 Actions | Edit 。

Choose the item desired for an update, and select Actions | Edit.

在 Edit Item 窗口中修改任何必要的属性或值。

Modify any attributes or values necessary in the Edit Item window.

Update Items Using Java

在项目更新操作中使用 Java 就需要创建一个表类实例，并调用其 updateItem 方法。然后，指定项目的键并提供详细的 UpdateExpression 属性修改。

Using Java in the item update operations requires creating a Table class instance, and calling its updateItem method. Then you specify the item’s primary key, and provide an UpdateExpression detailing attribute modifications.

以下是一个相同的示例 −

The Following is an example of the same −

DynamoDB dynamoDB = new DynamoDB(new AmazonDynamoDBClient(
   new ProfileCredentialsProvider()));

Table table = dynamoDB.getTable("ProductList");

Map<String, String> expressionAttributeNames = new HashMap<String, String>();
expressionAttributeNames.put("#M", "Make");
expressionAttributeNames.put("#P", "Price
expressionAttributeNames.put("#N", "ID");

Map<String, Object> expressionAttributeValues = new HashMap<String, Object>();
expressionAttributeValues.put(":val1",
   new HashSet<String>(Arrays.asList("Make1","Make2")));
expressionAttributeValues.put(":val2", 1);       //Price

UpdateItemOutcome outcome =  table.updateItem(
   "internalID",                                 // key attribute name
   111,                                          // key attribute value
   "add #M :val1 set #P = #P - :val2 remove #N", // UpdateExpression
   expressionAttributeNames,
   expressionAttributeValues);

updateItem 方法还允许指定条件，可以在以下示例中看到 −

The updateItem method also allows for specifying conditions, which can be seen in the following example −

Table table = dynamoDB.getTable("ProductList");
Map<String, String> expressionAttributeNames = new HashMap<String, String>();
expressionAttributeNames.put("#P", "Price");

Map<String, Object> expressionAttributeValues = new HashMap<String, Object>();
expressionAttributeValues.put(":val1", 44);  // change Price to 44
expressionAttributeValues.put(":val2", 15);  // only if currently 15

UpdateItemOutcome outcome = table.updateItem (new PrimaryKey("internalID",111),
   "set #P = :val1",                        // Update
   "#P = :val2",                            // Condition
   expressionAttributeNames,
   expressionAttributeValues);

Update Items Using Counters

DynamoDB 允许原子计数器，这意味着可以使用 UpdateItem 递增/递减属性值，而不会影响其他请求；此外，计数器总是更新。

DynamoDB allows atomic counters, which means using UpdateItem to increment/decrement attribute values without impacting other requests; furthermore, the counters always update.

以下是解释如何执行此操作的示例。

The following is an example that explains how it can be done.

Note − 以下示例可能假设之前创建过数据源。在尝试执行之前，获取支持库并创建必要的数据源（具有所需特性的表，或其他参考源）。

Note − The following sample may assume a previously created data source. Before attempting to execute, acquire supporting libraries and create necessary data sources (tables with required characteristics, or other referenced sources).

此示例还使用 Eclipse IDE、AWS 凭据文件和 Eclipse AWS Java 项目中的 AWS 工具包。

This sample also uses Eclipse IDE, an AWS credentials file, and the AWS Toolkit within an Eclipse AWS Java Project.

package com.amazonaws.codesamples.document;

import java.io.IOException;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;

import com.amazonaws.auth.profile.ProfileCredentialsProvider;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClient;
import com.amazonaws.services.dynamodbv2.document.DeleteItemOutcome;
import com.amazonaws.services.dynamodbv2.document.DynamoDB;
import com.amazonaws.services.dynamodbv2.document.Item;
import com.amazonaws.services.dynamodbv2.document.Table;

import com.amazonaws.services.dynamodbv2.document.UpdateItemOutcome;
import com.amazonaws.services.dynamodbv2.document.spec.DeleteItemSpec;
import com.amazonaws.services.dynamodbv2.document.spec.UpdateItemSpec;
import com.amazonaws.services.dynamodbv2.document.utils.NameMap;
import com.amazonaws.services.dynamodbv2.document.utils.ValueMap;
import com.amazonaws.services.dynamodbv2.model.ReturnValue;

public class UpdateItemOpSample {
   static DynamoDB dynamoDB = new DynamoDB(new AmazonDynamoDBClient(
      new ProfileCredentialsProvider()));
   static String tblName = "ProductList";

   public static void main(String[] args) throws IOException {
      createItems();
      retrieveItem();

      // Execute updates
      updateMultipleAttributes();
      updateAddNewAttribute();
      updateExistingAttributeConditionally();

      // Item deletion
      deleteItem();
   }
   private static void createItems() {
      Table table = dynamoDB.getTable(tblName);
      try {
         Item item = new Item()
            .withPrimaryKey("ID", 303)
            .withString("Nomenclature", "Polymer Blaster 4000")
            .withStringSet( "Manufacturers",
            new HashSet<String>(Arrays.asList("XYZ Inc.", "LMNOP Inc.")))
            .withNumber("Price", 50000)
            .withBoolean("InProduction", true)
            .withString("Category", "Laser Cutter");
            table.putItem(item);

         item = new Item()
            .withPrimaryKey("ID", 313)
            .withString("Nomenclature", "Agitatatron 2000")
            .withStringSet( "Manufacturers",
            new HashSet<String>(Arrays.asList("XYZ Inc,", "CDE Inc.")))
            .withNumber("Price", 40000)
            .withBoolean("InProduction", true)
            .withString("Category", "Agitator");
            table.putItem(item);
      } catch (Exception e) {
         System.err.println("Cannot create items.");
         System.err.println(e.getMessage());
      }
   }
   private static void updateAddNewAttribute() {
      Table table = dynamoDB.getTable(tableName);
      try {
         Map<String, String> expressionAttributeNames = new HashMap<String, String>();
         expressionAttributeNames.put("#na", "NewAttribute");
         UpdateItemSpec updateItemSpec = new UpdateItemSpec()
            .withPrimaryKey("ID", 303)
            .withUpdateExpression("set #na = :val1")
            .withNameMap(new NameMap()
            .with("#na", "NewAttribute"))
            .withValueMap(new ValueMap()
            .withString(":val1", "A value"))
            .withReturnValues(ReturnValue.ALL_NEW);
            UpdateItemOutcome outcome =  table.updateItem(updateItemSpec);

         // Confirm
         System.out.println("Displaying updated item...");
         System.out.println(outcome.getItem().toJSONPretty());
      } catch (Exception e) {
         System.err.println("Cannot add an attribute in " + tableName);
         System.err.println(e.getMessage());
      }
   }
}