使用Java创建DynamoDB表

在这篇文章中，我们将使用java方法在DynamoDB数据库上创建表。在开始之前，我们需要安装本地dynamodb，因为我们要避免使用dynamodb的任何费用。有一个以前的岗位上本地dynamodb。

如果您使用docker，则可以找到本地dynamodb映像，也可以按照此处所述自行创建一个。 dynamodb java sdk使我们能够使用java代码创建dynamodb表。

最基本的操作是使用哈希键创建表。在这种情况下，用户的电子邮件将是哈希密钥。

List<KeySchemaElement> elements = new ArrayList<KeySchemaElement>();KeySchemaElement keySchemaElement = new KeySchemaElement().withKeyType(KeyType.HASH).withAttributeName("email");elements.add(keySchemaElement);List<AttributeDefinition> attributeDefinitions = new ArrayList<>();attributeDefinitions.add(new AttributeDefinition().withAttributeName("email").withAttributeType(ScalarAttributeType.S));CreateTableRequest createTableRequest = new CreateTableRequest().withTableName("Users").withKeySchema(elements).withProvisionedThroughput(new ProvisionedThroughput().withReadCapacityUnits(5L).withWriteCapacityUnits(5L)).withAttributeDefinitions(attributeDefinitions);amazonDynamoDB.createTable(createTableRequest);

我们所做的是使用他的电子邮件作为哈希键创建Users表。下表称为“登录名”。每次用户登录时，登录都应保持跟踪。除了使用哈希键之外，我们还将使用范围键。

List<KeySchemaElement> elements = new ArrayList<KeySchemaElement>();KeySchemaElement hashKey = new KeySchemaElement().withKeyType(KeyType.HASH).withAttributeName("email");KeySchemaElement rangeKey = new KeySchemaElement().withKeyType(KeyType.RANGE).withAttributeName("timestamp");elements.add(hashKey);elements.add(rangeKey);List<AttributeDefinition> attributeDefinitions = new ArrayList<>();attributeDefinitions.add(new AttributeDefinition().withAttributeName("email").withAttributeType(ScalarAttributeType.S));attributeDefinitions.add(new AttributeDefinition().withAttributeName("timestamp").withAttributeType(ScalarAttributeType.N));CreateTableRequest createTableRequest = new CreateTableRequest().withTableName("Logins").withKeySchema(elements).withProvisionedThroughput(new ProvisionedThroughput().withReadCapacityUnits(5L).withWriteCapacityUnits(5L)).withAttributeDefinitions(attributeDefinitions);amazonDynamoDB.createTable(createTableRequest);

通过使用电子邮件作为哈希键，我们可以查询特定用户的登录名。通过使用登录发生的日期作为范围键，可以查找登录条目的排序或基于特定用户的登录日期执行高级查询。

但是，在大多数情况下，哈希键和范围键不足以满足我们的需求。 DynamoDB为我们提供了全局二级索引和本地二级索引。

我们将创建表SupervisorS。 Supervisor的哈希键将是他的名字。主管将为公司工作。该公司将成为我们的全球二级指数。由于公司拥有多个工厂，因此实地工厂将成为范围的关键。

List<KeySchemaElement> elements = new ArrayList<>();KeySchemaElement hashKey = new KeySchemaElement().withKeyType(KeyType.HASH).withAttributeName("name");elements.add(hashKey);List<GlobalSecondaryIndex> globalSecondaryIndices = new ArrayList<>();ArrayList<KeySchemaElement> indexKeySchema = new ArrayList<>();indexKeySchema.add(new KeySchemaElement().withAttributeName("company").withKeyType(KeyType.HASH));  //Partition keyindexKeySchema.add(new KeySchemaElement().withAttributeName("factory").withKeyType(KeyType.RANGE));  //Sort keyGlobalSecondaryIndex factoryIndex = new GlobalSecondaryIndex().withIndexName("FactoryIndex").withProvisionedThroughput(new ProvisionedThroughput().withReadCapacityUnits((long) 10).withWriteCapacityUnits((long) 1)).withKeySchema(indexKeySchema).withProjection(new Projection().withProjectionType(ProjectionType.ALL));globalSecondaryIndices.add(factoryIndex);List<AttributeDefinition> attributeDefinitions = new ArrayList<>();attributeDefinitions.add(new AttributeDefinition().withAttributeName("name").withAttributeType(ScalarAttributeType.S));attributeDefinitions.add(new AttributeDefinition().withAttributeName("company").withAttributeType(ScalarAttributeType.S));attributeDefinitions.add(new AttributeDefinition().withAttributeName("factory").withAttributeType(ScalarAttributeType.S));CreateTableRequest createTableRequest = new CreateTableRequest().withTableName("Supervisors").withKeySchema(elements).withProvisionedThroughput(new ProvisionedThroughput().withReadCapacityUnits(5L).withWriteCapacityUnits(5L)).withGlobalSecondaryIndexes(factoryIndex).withAttributeDefinitions(attributeDefinitions);amazonDynamoDB.createTable(createTableRequest);

下一个表将是公司表。哈希键将是母公司，范围键将是子公司。每个公司都有一位首席执行官。 CEO将是本地二级索引的范围键。

List<KeySchemaElement> elements = new ArrayList<>();KeySchemaElement hashKey = new KeySchemaElement().withKeyType(KeyType.HASH).withAttributeName("name");KeySchemaElement rangeKey = new KeySchemaElement().withKeyType(KeyType.RANGE).withAttributeName("subsidiary");elements.add(hashKey);elements.add(rangeKey);List<LocalSecondaryIndex> localSecondaryIndices = new ArrayList<>();ArrayList<KeySchemaElement> indexKeySchema = new ArrayList<>();indexKeySchema.add(new KeySchemaElement().withAttributeName("name").withKeyType(KeyType.HASH));indexKeySchema.add(new KeySchemaElement().withAttributeName("ceo").withKeyType(KeyType.RANGE));LocalSecondaryIndex ceoIndex = new LocalSecondaryIndex().withIndexName("CeoIndex").withKeySchema(indexKeySchema).withProjection(new Projection().withProjectionType(ProjectionType.ALL));localSecondaryIndices.add(ceoIndex);List<AttributeDefinition> attributeDefinitions = new ArrayList<>();attributeDefinitions.add(new AttributeDefinition().withAttributeName("name").withAttributeType(ScalarAttributeType.S));attributeDefinitions.add(new AttributeDefinition().withAttributeName("subsidiary").withAttributeType(ScalarAttributeType.S));attributeDefinitions.add(new AttributeDefinition().withAttributeName("ceo").withAttributeType(ScalarAttributeType.S));CreateTableRequest createTableRequest = new CreateTableRequest().withTableName("Companies").withKeySchema(elements).withProvisionedThroughput(new ProvisionedThroughput().withReadCapacityUnits(5L).withWriteCapacityUnits(5L)).withLocalSecondaryIndexes(localSecondaryIndices).withAttributeDefinitions(attributeDefinitions);amazonDynamoDB.createTable(createTableRequest);

您可以在github上找到源代码。