# 处理全局二级索引：.NET
您可以使用 适用于 .NET 的 AWS SDK 低级 API 创建具有一个或多个全局二级索引的 Amazon DynamoDB 表、描述表中的索引，以及使用索引执行查询。这些操作映射到对应的 DynamoDB 操作。有关更多信息，请参阅 [Amazon DynamoDB API 参考](https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/)。
以下是使用 .NET 低级 API 执行表操作的常见步骤。
1. 创建 `AmazonDynamoDBClient` 类的实例。
1. 通过创建对应的请求对象，为操作提供必需参数和可选参数。
例如，创建一个 `CreateTableRequest` 对象以创建表；创建一个 `QueryRequest` 数据元以查询表或索引。
1. 执行您在前面步骤中创建的客户端提供的适当方法。
**Topics**
+ [创建一个具有全局二级索引的表。](#GSILowLevelDotNet.CreateTableWithIndex)
+ [描述一个具有全局二级索引的表](#GSILowLevelDotNet.DescribeTableWithIndex)
+ [查询全局二级索引](#GSILowLevelDotNet.QueryAnIndex)
+ [示例：使用 适用于 .NET 的 AWS SDK 低级 API 的全局二级索引](GSILowLevelDotNet.Example.md)
## 创建一个具有全局二级索引的表。
创建表时可以同时创建全局二级索引。为此，请使用 `CreateTable` 并为一个或多个全局二级索引提供您的规范。以下 C\$1 代码示例创建一个保存天气数据信息的表。分区键为 `Location`，排序键为 `Date`。全局二级索引 `PrecipIndex` 允许快速访问各个位置的降水数据。
以下是使用 .NET 低级别 API 创建具有全局二级索引的表的步骤。
1. 创建 `AmazonDynamoDBClient` 类的实例。
1. 创建 `CreateTableRequest` 类实例，以提供请求信息。
您必须提供表名称、主键以及预配置吞吐量值。对于全局二级索引，您必须提供索引名称、其预置的吞吐量设置、索引排序键的属性定义、索引的键架构以及属性投影。
1. 以参数形式提供请求对象，运行 `CreateTable` 方法。
以下 C\$1 代码示例演示了上述步骤。创建具有全局二级索引 (`PrecipIndex`) 的表 (`WeatherData`)。索引分区键为 `Date`，排序键为 `Precipitation`。所有表属性都投影到索引中。用户可以查询此索引以获取特定日期的天气数据，也可以选择按降水量对数据进行排序。
由于 `Precipitation` 不是表的键属性，它不是必需的。然而,`WeatherData` 项目不包含 `Precipitation`，不会显示在 `PrecipIndex` 中。
```
client = new AmazonDynamoDBClient();
string tableName = "WeatherData";
// Attribute definitions
var attributeDefinitions = new List()
{
{new AttributeDefinition{
AttributeName = "Location",
AttributeType = "S"}},
{new AttributeDefinition{
AttributeName = "Date",
AttributeType = "S"}},
{new AttributeDefinition(){
AttributeName = "Precipitation",
AttributeType = "N"}
}
};
// Table key schema
var tableKeySchema = new List()
{
{new KeySchemaElement {
AttributeName = "Location",
KeyType = "HASH"}}, //Partition key
{new KeySchemaElement {
AttributeName = "Date",
KeyType = "RANGE"} //Sort key
}
};
// PrecipIndex
var precipIndex = new GlobalSecondaryIndex
{
IndexName = "PrecipIndex",
ProvisionedThroughput = new ProvisionedThroughput
{
ReadCapacityUnits = (long)10,
WriteCapacityUnits = (long)1
},
Projection = new Projection { ProjectionType = "ALL" }
};
var indexKeySchema = new List {
{new KeySchemaElement { AttributeName = "Date", KeyType = "HASH"}}, //Partition key
{new KeySchemaElement{AttributeName = "Precipitation",KeyType = "RANGE"}} //Sort key
};
precipIndex.KeySchema = indexKeySchema;
CreateTableRequest createTableRequest = new CreateTableRequest
{
TableName = tableName,
ProvisionedThroughput = new ProvisionedThroughput
{
ReadCapacityUnits = (long)5,
WriteCapacityUnits = (long)1
},
AttributeDefinitions = attributeDefinitions,
KeySchema = tableKeySchema,
GlobalSecondaryIndexes = { precipIndex }
};
CreateTableResponse response = client.CreateTable(createTableRequest);
Console.WriteLine(response.CreateTableResult.TableDescription.TableName);
Console.WriteLine(response.CreateTableResult.TableDescription.TableStatus);
```
您必须等待 DynamoDB 创建该表并将表的状态设置为 `ACTIVE`。然后，您就可以开始在表中添加数据项目。
## 描述一个具有全局二级索引的表
要获取表上全局二级索引的信息，请使用 `DescribeTable`。对于每个索引，您都可以查看其名称、键架构和投影的属性。
以下介绍使用 .NET 低级 API 访问表中全局二级索引信息的步骤。
1. 创建 `AmazonDynamoDBClient` 类的实例。
1. 以参数形式提供请求对象，运行 `describeTable` 方法。
创建 `DescribeTableRequest` 类实例，以提供请求信息。您必须提供表名称。
以下 C\$1 代码示例演示了上述步骤。
**Example**
```
client = new AmazonDynamoDBClient();
string tableName = "WeatherData";
DescribeTableResponse response = client.DescribeTable(new DescribeTableRequest { TableName = tableName});
List globalSecondaryIndexes =
response.DescribeTableResult.Table.GlobalSecondaryIndexes;
// This code snippet will work for multiple indexes, even though
// there is only one index in this example.
foreach (GlobalSecondaryIndexDescription gsiDescription in globalSecondaryIndexes) {
Console.WriteLine("Info for index " + gsiDescription.IndexName + ":");
foreach (KeySchemaElement kse in gsiDescription.KeySchema) {
Console.WriteLine("\t" + kse.AttributeName + ": key type is " + kse.KeyType);
}
Projection projection = gsiDescription.Projection;
Console.WriteLine("\tThe projection type is: " + projection.ProjectionType);
if (projection.ProjectionType.ToString().Equals("INCLUDE")) {
Console.WriteLine("\t\tThe non-key projected attributes are: "
+ projection.NonKeyAttributes);
}
}
```
## 查询全局二级索引
您可以对全局二级索引使用 `Query`，基本上与对表执行 `Query` 操作相同。您需要指定索引名称、索引分区键和排序键（如果有）的查询条件以及要返回的属性。在本示例中，索引是 `PrecipIndex`，其分区键为 `Date`，排序键 `Precipitation`。索引查询返回特定日期降水量大于零的所有天气数据。
以下是使用 .NET 低级别 API 查询全局二级索引的步骤。
1. 创建 `AmazonDynamoDBClient` 类的实例。
1. 创建 `QueryRequest` 类实例，以提供请求信息。
1. 以参数形式提供请求对象，运行 `query` 方法。
属性名称 `Date` 是 DynamoDB 保留关键字。因此，您必须将表达式属性名称用作 `KeyConditionExpression` 的占位符。
以下 C\$1 代码示例演示了上述步骤。
**Example**
```
client = new AmazonDynamoDBClient();
QueryRequest queryRequest = new QueryRequest
{
TableName = "WeatherData",
IndexName = "PrecipIndex",
KeyConditionExpression = "#dt = :v_date and Precipitation > :v_precip",
ExpressionAttributeNames = new Dictionary {
{"#dt", "Date"}
},
ExpressionAttributeValues = new Dictionary {
{":v_date", new AttributeValue { S = "2013-08-01" }},
{":v_precip", new AttributeValue { N = "0" }}
},
ScanIndexForward = true
};
var result = client.Query(queryRequest);
var items = result.Items;
foreach (var currentItem in items)
{
foreach (string attr in currentItem.Keys)
{
Console.Write(attr + "---> ");
if (attr == "Precipitation")
{
Console.WriteLine(currentItem[attr].N);
}
else
{
Console.WriteLine(currentItem[attr].S);
}
}
Console.WriteLine();
}
```
# 示例：使用 适用于 .NET 的 AWS SDK 低级 API 的全局二级索引
以下 C\$1 代码示例显示如何处理全局二级索引。本示例创建了一个 `Issues` 表，可以用于软件开发的简单错误跟踪系统。分区键为 `IssueId`，排序键为 `Title`。此表上有 3 个全局二级索引：
+ `CreateDateIndex` — 分区键为 `CreateDate`，排序键为 `IssueId`。除了表键之外，属性 `Description` 和 `Status` 投影到索引中。
+ `TitleIndex` — 分区键为 `Title`，排序键为 `IssueId`。表键以外的其他属性都不投影到索引中。
+ `DueDateIndex` — 分区键为 `DueDate`；没有排序键。所有表属性都投影到索引中。
创建 `Issues` 表后，程序为该表加载表示软件问题报告的数据。然后使用全局二级索引查询这些数据。最后，程序会删除 `Issues` 表。
有关测试以下示例的分步说明，请参阅 [.NET 代码示例](CodeSamples.DotNet.md)。
**Example**
```
using System;
using System.Collections.Generic;
using System.Linq;
using Amazon.DynamoDBv2;
using Amazon.DynamoDBv2.DataModel;
using Amazon.DynamoDBv2.DocumentModel;
using Amazon.DynamoDBv2.Model;
using Amazon.Runtime;
using Amazon.SecurityToken;
namespace com.amazonaws.codesamples
{
class LowLevelGlobalSecondaryIndexExample
{
private static AmazonDynamoDBClient client = new AmazonDynamoDBClient();
public static String tableName = "Issues";
public static void Main(string[] args)
{
CreateTable();
LoadData();
QueryIndex("CreateDateIndex");
QueryIndex("TitleIndex");
QueryIndex("DueDateIndex");
DeleteTable(tableName);
Console.WriteLine("To continue, press enter");
Console.Read();
}
private static void CreateTable()
{
// Attribute definitions
var attributeDefinitions = new List()
{
{new AttributeDefinition {
AttributeName = "IssueId", AttributeType = "S"
}},
{new AttributeDefinition {
AttributeName = "Title", AttributeType = "S"
}},
{new AttributeDefinition {
AttributeName = "CreateDate", AttributeType = "S"
}},
{new AttributeDefinition {
AttributeName = "DueDate", AttributeType = "S"
}}
};
// Key schema for table
var tableKeySchema = new List() {
{
new KeySchemaElement {
AttributeName= "IssueId",
KeyType = "HASH" //Partition key
}
},
{
new KeySchemaElement {
AttributeName = "Title",
KeyType = "RANGE" //Sort key
}
}
};
// Initial provisioned throughput settings for the indexes
var ptIndex = new ProvisionedThroughput
{
ReadCapacityUnits = 1L,
WriteCapacityUnits = 1L
};
// CreateDateIndex
var createDateIndex = new GlobalSecondaryIndex()
{
IndexName = "CreateDateIndex",
ProvisionedThroughput = ptIndex,
KeySchema = {
new KeySchemaElement {
AttributeName = "CreateDate", KeyType = "HASH" //Partition key
},
new KeySchemaElement {
AttributeName = "IssueId", KeyType = "RANGE" //Sort key
}
},
Projection = new Projection
{
ProjectionType = "INCLUDE",
NonKeyAttributes = {
"Description", "Status"
}
}
};
// TitleIndex
var titleIndex = new GlobalSecondaryIndex()
{
IndexName = "TitleIndex",
ProvisionedThroughput = ptIndex,
KeySchema = {
new KeySchemaElement {
AttributeName = "Title", KeyType = "HASH" //Partition key
},
new KeySchemaElement {
AttributeName = "IssueId", KeyType = "RANGE" //Sort key
}
},
Projection = new Projection
{
ProjectionType = "KEYS_ONLY"
}
};
// DueDateIndex
var dueDateIndex = new GlobalSecondaryIndex()
{
IndexName = "DueDateIndex",
ProvisionedThroughput = ptIndex,
KeySchema = {
new KeySchemaElement {
AttributeName = "DueDate",
KeyType = "HASH" //Partition key
}
},
Projection = new Projection
{
ProjectionType = "ALL"
}
};
var createTableRequest = new CreateTableRequest
{
TableName = tableName,
ProvisionedThroughput = new ProvisionedThroughput
{
ReadCapacityUnits = (long)1,
WriteCapacityUnits = (long)1
},
AttributeDefinitions = attributeDefinitions,
KeySchema = tableKeySchema,
GlobalSecondaryIndexes = {
createDateIndex, titleIndex, dueDateIndex
}
};
Console.WriteLine("Creating table " + tableName + "...");
client.CreateTable(createTableRequest);
WaitUntilTableReady(tableName);
}
private static void LoadData()
{
Console.WriteLine("Loading data into table " + tableName + "...");
// IssueId, Title,
// Description,
// CreateDate, LastUpdateDate, DueDate,
// Priority, Status
putItem("A-101", "Compilation error",
"Can't compile Project X - bad version number. What does this mean?",
"2013-11-01", "2013-11-02", "2013-11-10",
1, "Assigned");
putItem("A-102", "Can't read data file",
"The main data file is missing, or the permissions are incorrect",
"2013-11-01", "2013-11-04", "2013-11-30",
2, "In progress");
putItem("A-103", "Test failure",
"Functional test of Project X produces errors",
"2013-11-01", "2013-11-02", "2013-11-10",
1, "In progress");
putItem("A-104", "Compilation error",
"Variable 'messageCount' was not initialized.",
"2013-11-15", "2013-11-16", "2013-11-30",
3, "Assigned");
putItem("A-105", "Network issue",
"Can't ping IP address 127.0.0.1. Please fix this.",
"2013-11-15", "2013-11-16", "2013-11-19",
5, "Assigned");
}
private static void putItem(
String issueId, String title,
String description,
String createDate, String lastUpdateDate, String dueDate,
Int32 priority, String status)
{
Dictionary item = new Dictionary();
item.Add("IssueId", new AttributeValue
{
S = issueId
});
item.Add("Title", new AttributeValue
{
S = title
});
item.Add("Description", new AttributeValue
{
S = description
});
item.Add("CreateDate", new AttributeValue
{
S = createDate
});
item.Add("LastUpdateDate", new AttributeValue
{
S = lastUpdateDate
});
item.Add("DueDate", new AttributeValue
{
S = dueDate
});
item.Add("Priority", new AttributeValue
{
N = priority.ToString()
});
item.Add("Status", new AttributeValue
{
S = status
});
try
{
client.PutItem(new PutItemRequest
{
TableName = tableName,
Item = item
});
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
private static void QueryIndex(string indexName)
{
Console.WriteLine
("\n***********************************************************\n");
Console.WriteLine("Querying index " + indexName + "...");
QueryRequest queryRequest = new QueryRequest
{
TableName = tableName,
IndexName = indexName,
ScanIndexForward = true
};
String keyConditionExpression;
Dictionary expressionAttributeValues = new Dictionary();
if (indexName == "CreateDateIndex")
{
Console.WriteLine("Issues filed on 2013-11-01\n");
keyConditionExpression = "CreateDate = :v_date and begins_with(IssueId, :v_issue)";
expressionAttributeValues.Add(":v_date", new AttributeValue
{
S = "2013-11-01"
});
expressionAttributeValues.Add(":v_issue", new AttributeValue
{
S = "A-"
});
}
else if (indexName == "TitleIndex")
{
Console.WriteLine("Compilation errors\n");
keyConditionExpression = "Title = :v_title and begins_with(IssueId, :v_issue)";
expressionAttributeValues.Add(":v_title", new AttributeValue
{
S = "Compilation error"
});
expressionAttributeValues.Add(":v_issue", new AttributeValue
{
S = "A-"
});
// Select
queryRequest.Select = "ALL_PROJECTED_ATTRIBUTES";
}
else if (indexName == "DueDateIndex")
{
Console.WriteLine("Items that are due on 2013-11-30\n");
keyConditionExpression = "DueDate = :v_date";
expressionAttributeValues.Add(":v_date", new AttributeValue
{
S = "2013-11-30"
});
// Select
queryRequest.Select = "ALL_PROJECTED_ATTRIBUTES";
}
else
{
Console.WriteLine("\nNo valid index name provided");
return;
}
queryRequest.KeyConditionExpression = keyConditionExpression;
queryRequest.ExpressionAttributeValues = expressionAttributeValues;
var result = client.Query(queryRequest);
var items = result.Items;
foreach (var currentItem in items)
{
foreach (string attr in currentItem.Keys)
{
if (attr == "Priority")
{
Console.WriteLine(attr + "---> " + currentItem[attr].N);
}
else
{
Console.WriteLine(attr + "---> " + currentItem[attr].S);
}
}
Console.WriteLine();
}
}
private static void DeleteTable(string tableName)
{
Console.WriteLine("Deleting table " + tableName + "...");
client.DeleteTable(new DeleteTableRequest
{
TableName = tableName
});
WaitForTableToBeDeleted(tableName);
}
private static void WaitUntilTableReady(string tableName)
{
string status = null;
// Let us wait until table is created. Call DescribeTable.
do
{
System.Threading.Thread.Sleep(5000); // Wait 5 seconds.
try
{
var res = client.DescribeTable(new DescribeTableRequest
{
TableName = tableName
});
Console.WriteLine("Table name: {0}, status: {1}",
res.Table.TableName,
res.Table.TableStatus);
status = res.Table.TableStatus;
}
catch (ResourceNotFoundException)
{
// DescribeTable is eventually consistent. So you might
// get resource not found. So we handle the potential exception.
}
} while (status != "ACTIVE");
}
private static void WaitForTableToBeDeleted(string tableName)
{
bool tablePresent = true;
while (tablePresent)
{
System.Threading.Thread.Sleep(5000); // Wait 5 seconds.
try
{
var res = client.DescribeTable(new DescribeTableRequest
{
TableName = tableName
});
Console.WriteLine("Table name: {0}, status: {1}",
res.Table.TableName,
res.Table.TableStatus);
}
catch (ResourceNotFoundException)
{
tablePresent = false;
}
}
}
}
}
```