在我看来,你想做一个有条件的PutItem
在此表上:如果没有其他相同的项目,则将该项目放入表中customer_id
。这很容易做到,因为customer_id
是表的哈希键。来自PutItem
文档:
Note
要防止新项目替换现有项目,请使用条件 put 操作比较运算符 set to NULL
为了
主键属性,或属性。
以下是我使用 Java SDK 中的 Dynamo DB 文档 API 编写并针对 DynamoDB Local 运行的快速示例:
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);
}
}
Output:
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: {custo[email protected], customer_name=Jim, customer_id=ABCD} }