使用本機次要索引：.NET

您可以使用 AWS SDK for .NET 低階 API 建立含有一或多個本機次要索引的 Amazon DynamoDB 資料表、描述資料表上的索引，以及使用索引執行查詢。這些操作會映射至對應的低階 DynamoDB API 動作。如需詳細資訊，請參閱 .NET 程式碼範例。

下列是使用 .NET 低階 API 執行資料表操作的一般步驟。

使用本機次要索引建立資料表

您必須同時建立資料表和本機次要索引。若要執行這項操作，請使用 CreateTable，並提供一或多個本機次要索引的規格。以下 C# 程式碼範例會建立資料表來保存音樂收藏中歌曲的相關資訊。分割區索引鍵為 Artist，而排序索引鍵為 SongTitle。次要索引 AlbumTitleIndex 有助於依照專輯標題查詢。

以下是使用 .NET 低階 API 建立具有本機次要索引之資料表的步驟。

下列 C# 程式碼範例示範前述步驟。程式碼會建立一個資料表 (Music) 與次要索引 AlbumTitle 屬性。資料表分割區索引鍵和排序索引鍵以及索引排序索引鍵，是唯一投影到索引的屬性。

AmazonDynamoDBClient client = new AmazonDynamoDBClient();
string tableName = "Music";

CreateTableRequest createTableRequest = new CreateTableRequest()
{
    TableName = tableName
};

//ProvisionedThroughput
createTableRequest.ProvisionedThroughput = new ProvisionedThroughput()
{
    ReadCapacityUnits = (long)5,
    WriteCapacityUnits = (long)5
};

//AttributeDefinitions
List<AttributeDefinition> attributeDefinitions = new List<AttributeDefinition>();

attributeDefinitions.Add(new AttributeDefinition()
{
    AttributeName = "Artist",
    AttributeType = "S"
});

attributeDefinitions.Add(new AttributeDefinition()
 {
     AttributeName = "SongTitle",
     AttributeType = "S"
 });

attributeDefinitions.Add(new AttributeDefinition()
 {
     AttributeName = "AlbumTitle",
     AttributeType = "S"
 });

createTableRequest.AttributeDefinitions = attributeDefinitions;

//KeySchema
List<KeySchemaElement> tableKeySchema = new List<KeySchemaElement>();

tableKeySchema.Add(new KeySchemaElement() { AttributeName = "Artist", KeyType = "HASH" });  //Partition key
tableKeySchema.Add(new KeySchemaElement() { AttributeName = "SongTitle", KeyType = "RANGE" });  //Sort key

createTableRequest.KeySchema = tableKeySchema;

List<KeySchemaElement> indexKeySchema = new List<KeySchemaElement>();
indexKeySchema.Add(new KeySchemaElement() { AttributeName = "Artist", KeyType = "HASH" });  //Partition key
indexKeySchema.Add(new KeySchemaElement() { AttributeName = "AlbumTitle", KeyType = "RANGE" });  //Sort key

Projection projection = new Projection() { ProjectionType = "INCLUDE" };

List<string> nonKeyAttributes = new List<string>();
nonKeyAttributes.Add("Genre");
nonKeyAttributes.Add("Year");
projection.NonKeyAttributes = nonKeyAttributes;

LocalSecondaryIndex localSecondaryIndex = new LocalSecondaryIndex()
{
    IndexName = "AlbumTitleIndex",
    KeySchema = indexKeySchema,
    Projection = projection
};

List<LocalSecondaryIndex> localSecondaryIndexes = new List<LocalSecondaryIndex>();
localSecondaryIndexes.Add(localSecondaryIndex);
createTableRequest.LocalSecondaryIndexes = localSecondaryIndexes;

CreateTableResponse result = client.CreateTable(createTableRequest);
Console.WriteLine(result.CreateTableResult.TableDescription.TableName);
Console.WriteLine(result.CreateTableResult.TableDescription.TableStatus);

您必須等到 DynamoDB 建立資料表，並將資料表狀態設定為 ACTIVE。之後，您可以開始將資料項目放入資料表中。

使用本機次要索引描述資料表

若要取得資料表上本機次要索引的資訊，請使用 DescribeTable API。對於每個索引，您可以存取其名稱、索引鍵結構描述和投影屬性。

以下是使用 .NET 低階 API 存取資料表的本機次要索引資訊的步驟。

下列 C# 程式碼範例示範前述步驟。

AmazonDynamoDBClient client = new AmazonDynamoDBClient();
string tableName = "Music";

DescribeTableResponse response = client.DescribeTable(new DescribeTableRequest() { TableName = tableName });
List<LocalSecondaryIndexDescription> localSecondaryIndexes =
    response.DescribeTableResult.Table.LocalSecondaryIndexes;

// This code snippet will work for multiple indexes, even though
// there is only one index in this example.
foreach (LocalSecondaryIndexDescription lsiDescription in localSecondaryIndexes)
{
    Console.WriteLine("Info for index " + lsiDescription.IndexName + ":");

    foreach (KeySchemaElement kse in lsiDescription.KeySchema)
    {
        Console.WriteLine("\t" + kse.AttributeName + ": key type is " + kse.KeyType);
    }

    Projection projection = lsiDescription.Projection;

    Console.WriteLine("\tThe projection type is: " + projection.ProjectionType);

    if (projection.ProjectionType.ToString().Equals("INCLUDE"))
    {
        Console.WriteLine("\t\tThe non-key projected attributes are:");

        foreach (String s in projection.NonKeyAttributes)
        {
            Console.WriteLine("\t\t" + s);
        }

    }
}

查詢本機次要索引

您可以依照與 Query 資料表大致相同的方式在本機次要索引上使用 Query。您必須指定索引名稱、索引排序索引鍵的查詢準則，以及您要傳回的屬性。在本例中，索引是 AlbumTitleIndex，而索引排序索引鍵為 AlbumTitle。

傳回的唯一屬性是已投影到索引的屬性。您也可以修改此查詢來選擇非索引鍵屬性，但這需要相對昂貴的資料表擷取活動。如需資料表擷取的詳細資訊，請參閱 屬性投影

以下是使用 .NET 低階 API 查詢本機次要索引的步驟。

下列 C# 程式碼範例示範前述步驟。

QueryRequest queryRequest = new QueryRequest
{
    TableName = "Music",
    IndexName = "AlbumTitleIndex",
    Select = "ALL_ATTRIBUTES",
    ScanIndexForward = true,
    KeyConditionExpression = "Artist = :v_artist and AlbumTitle = :v_title",
    ExpressionAttributeValues = new Dictionary<string, AttributeValue>()
    {
        {":v_artist",new AttributeValue {S = "Acme Band"}},
        {":v_title",new AttributeValue {S = "Songs About Life"}}
    },
};

QueryResponse response = client.Query(queryRequest);

foreach (var attribs in response.Items)
{
    foreach (var attrib in attribs)
    {
        Console.WriteLine(attrib.Key + " ---> " + attrib.Value.S);
    }
    Console.WriteLine();
}