Dynamodb 简明教程

DynamoDB - Creating Items

在 DynamoDB 中创建项目主要包括项目和属性规范，以及指定条件的选项。每个项目都作为一个属性集存在，每个属性都命名并分配了特定类型的某个值。

Creating an item in DynamoDB consists primarily of item and attribute specification, and the option of specifying conditions. Each item exists as a set of attributes, with each attribute named and assigned a value of a certain type.

值类型包括标量、文档或集合。项目的尺寸限制为 400KB，但在该限制内可以容纳的属性数量不受限制。名称和值大小（二进制和 UTF-8 长度）决定项目大小。使用短属性名称有助于减小项目大小。

Value types include scalar, document, or set. Items carry a 400KB size limit, with the possibility of any amount of attributes capable of fitting within that limit. Name and value sizes (binary and UTF-8 lengths) determine item size. Using short attribute names aids in minimizing item size.

Note − 您必须指定所有主键属性，而主键只需分区键即可；复合键则需要分区键和排序键。

Note − You must specify all primary key attributes, with primary keys only requiring the partition key; and composite keys requiring both the partition and sort key.

另外，请记住表不拥有预定义架构。您可以在一张表中存储截然不同的数据集。

Also, remember tables possess no predefined schema. You can store dramatically different datasets in one table.

使用 GUI 控制台、Java 或其他工具来执行此任务。

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

How to Create an Item Using the GUI Console?

导航到控制台。在左侧导航窗格中，选择 Tables 。选择用作目标的表名，然后选择 Items 选项卡，如下面的屏幕截图所示。

Navigate to the console. In the navigation pane on the left side, select Tables. Choose the table name for use as the destination, and then select the Items tab as shown in the following screenshot.

选择 Create Item 。创建项目屏幕提供了一个用于输入所需属性值的界面。还必须输入任何辅助索引。

Select Create Item. The Create Item screen provides an interface for entering the required attribute values. Any secondary indices must also be entered.

如果您需要更多属性，请选择 Message 左边的操作菜单。然后选择 Append 和所需的数据类型。

If you require more attributes, select the action menu on the left of the Message. Then select Append, and the desired data type.

在输入所有必要信息后，选择 Save 以添加项目。

After entering all essential information, select Save to add the item.

How to Use Java in Item Creation?

在项目创建操作中使用 Java 包括创建 DynamoDB 类实例、Table 类实例、Item 类实例，以及指定要创建的项目的主键和属性。然后使用 putItem 方法添加新项目。

Using Java in item creation operations consists of creating a DynamoDB class instance, Table class instance, Item class instance, and specifying the primary key and attributes of the item you will create. Then add your new item with the putItem method.

Example

DynamoDB dynamoDB = new DynamoDB (new AmazonDynamoDBClient(
   new ProfileCredentialsProvider()));
Table table = dynamoDB.getTable("ProductList");

// Spawn a related items list
List<Number> RELItems = new ArrayList<Number>();
RELItems.add(123);
RELItems.add(456);
RELItems.add(789);

//Spawn a product picture map
Map<String, String> photos = new HashMap<String, String>();
photos.put("Anterior", "http://xyz.com/products/101_front.jpg");
photos.put("Posterior", "http://xyz.com/products/101_back.jpg");
photos.put("Lateral", "http://xyz.com/products/101_LFTside.jpg");

//Spawn a product review map
Map<String, List<String>> prodReviews = new HashMap<String, List<String>>();
List<String> fiveStarRVW = new ArrayList<String>();
fiveStarRVW.add("Shocking high performance.");
fiveStarRVW.add("Unparalleled in its market.");
prodReviews.put("5 Star", fiveStarRVW);
List<String> oneStarRVW = new ArrayList<String>();
oneStarRVW.add("The worst offering in its market.");
prodReviews.put("1 Star", oneStarRVW);

// Generate the item
Item item = new Item()
   .withPrimaryKey("Id", 101)
   .withString("Nomenclature", "PolyBlaster 101")
   .withString("Description", "101 description")
   .withString("Category", "Hybrid Power Polymer Cutter")
   .withString("Make", "Brand – XYZ")
   .withNumber("Price", 50000)
   .withString("ProductCategory", "Laser Cutter")
   .withBoolean("Availability", true)
   .withNull("Qty")
   .withList("ItemsRelated", RELItems)
   .withMap("Images", photos)
   .withMap("Reviews", prodReviews);

// Add item to the table
PutItemOutcome outcome = table.putItem(item);

您还可以查看以下更大的示例。

You can also look at the following larger example.

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).

以下示例还使用 Eclipse IDE、AWS 凭证文件以及 Eclipse AWS Java 项目中的 AWS Toolkit。

The following 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 CreateItemOpSample {
   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());
      }
   }
}