在关系数据库中,参数化查询是一种查询,其中占位符用于参数,参数值在执行时提供. DocumentDB还支持参数化查询,参数化查询中的参数可以用熟悉的@表示法表示.使用参数化查询的最重要原因是避免SQL注入攻击.它还可以提供强大的处理和用户输入的转义.
让我们看一下我们将使用.Net SDK的示例.以下是将删除集合的代码.
private async static Task DeleteCollection(DocumentClient client, string collectionId) { Console.WriteLine(); Console.WriteLine(">>> Delete Collection {0} in {1} <<<", collectionId, _database.Id); var query = new SqlQuerySpec { QueryText = "SELECT * FROM c WHERE c.id = @id", Parameters = new SqlParameterCollection { new SqlParameter { Name = "@id", Value = collectionId } } }; DocumentCollection collection = client.CreateDocumentCollectionQuery(database.SelfLink, query).AsEnumerable().First(); await client.DeleteDocumentCollectionAsync(collection.SelfLink); Console.WriteLine("Deleted collection {0} from database {1}", collectionId, _database.Id); }
参数化查询的构造如下:
var query = new SqlQuerySpec { QueryText = "SELECT * FROM c WHERE c.id = @id", Parameters = new SqlParameterCollection { new SqlParameter { Name = "@id", Value = collectionId } } };
我们没有对collectionId进行硬编码,因此可以使用此方法删除任何集合.我们可以使用'@'符号来为参数名称添加前缀,类似于SQL Server.
在上面的示例中,我们通过Id查询特定集合,其中Id参数在此定义SqlParameterCollection分配给此SqlQuerySpec的参数属性.然后,SDK完成构建DocumentDB的最终查询字符串的工作,其中嵌入了collectionId.我们运行查询,然后使用其SelfLink删除集合.
以下是CreateDocumentClient任务实现.
private static async Task CreateDocumentClient() { // Create a new instance of the DocumentClient using (var client = new DocumentClient(new Uri(EndpointUrl), AuthorizationKey)) { database = client.CreateDatabaseQuery("SELECT * FROM c WHERE c.id = 'earthquake'").AsEnumerable().First(); collection = client.CreateDocumentCollectionQuery(database.CollectionsLink, "SELECT * FROM c WHERE c.id = 'myfirstdb'").AsEnumerable().First(); await DeleteCollection(client, "MyCollection1"); await DeleteCollection(client, "MyCollection2"); } }
执行代码时,会产生以下输出.
**** Delete Collection MyCollection1 in mydb **** Deleted collection MyCollection1 from database myfirstdb **** Delete Collection MyCollection2 in mydb **** Deleted collection MyCollection2 from database myfirstdb
让我们看看另一个例子.我们可以编写一个以姓氏和地址状态为参数的查询,然后根据用户输入为lastname和location.state的各种值执行它.
SELECT * FROM Families f WHERE f.lastName = @lastName AND f.location.state = @addressState
然后可以将此请求作为参数化JSON查询发送到DocumentDB,如以下代码所示.
{ "query": "SELECT * FROM Families f WHERE f.lastName = @lastName AND f.location.state = @addressState", "parameters": [ {"name": "@lastName", "value": "Wakefield"}, {"name": "@addressState", "value": "NY"}, ] }