📌  相关文章
📜  DocumentDB SQL-用户定义的函数

📅  最后修改于: 2020-11-28 13:40:02             🧑  作者: Mango

DocumentDB SQL提供对用户定义函数(UDF)的支持。 UDF只是您可以编写的另一种JavaScript函数，它们的功能与您期望的差不多。您可以创建UDF，以使用可在查询中引用的自定义业务逻辑来扩展查询语言。

使用这些UDF扩展了DocumentDB SQL语法，以支持自定义应用程序逻辑。 UDF可以在DocumentDB中注册，然后在SQL查询中被引用。

让我们考虑此示例的以下三个文档。

AndersenFamily文件如下。

{ 
   "id": "AndersenFamily", 
   "lastName": "Andersen", 
    
   "parents": [ 
      { "firstName": "Thomas", "relationship":  "father" }, 
      { "firstName": "Mary Kay", "relationship":  "mother" } 
   ],
   
   "children": [ 
      { 
         "firstName": "Henriette Thaulow", 
         "gender": "female", 
         "grade": 5, 
         "pets": [ { "givenName": "Fluffy", "type":  "Rabbit" } ] 
      } 
   ],
   
   "location": { "state": "WA", "county": "King", "city": "Seattle" }, 
   "isRegistered": true 
}

SmithFamily文件如下。

{ 
   "id": "SmithFamily", 
    
   "parents": [ 
      { "familyName": "Smith", "givenName": "James" }, 
      { "familyName": "Curtis", "givenName": "Helen" }
   ], 
    
   "children": [ 
      { 
         "givenName": "Michelle", 
         "gender": "female", 
         "grade": 1 
      }, 
        
      { 
         "givenName": "John", 
         "gender": "male", 
         "grade": 7,
            
         "pets": [ 
            { "givenName": "Tweetie", "type": "Bird" } 
         ] 
      }
   ],
   
   "location": { 
      "state": "NY", 
      "county": "Queens", 
      "city": "Forest Hills" 
   },
   
   "isRegistered": true 
}

WakefieldFamily文件如下。

{ 
   "id": "WakefieldFamily", 
    
   "parents": [ 
      { "familyName": "Wakefield", "givenName": "Robin" }, 
      { "familyName": "Miller", "givenName": "Ben" } 
   ],
   
   "children": [ 
      { 
         "familyName": "Merriam", 
         "givenName": "Jesse", 
         "gender": "female", 
         "grade": 6,
            
         "pets": [
            { "givenName": "Charlie Brown", "type": "Dog" }, 
            { "givenName": "Tiger", "type": "Cat" }, 
            { "givenName": "Princess", "type": "Cat" } 
         ] 
      },
        
      { 
         "familyName": "Miller", 
         "givenName": "Lisa", 
         "gender": "female", 
         "grade": 3,
            
         "pets": [ 
            { "givenName": "Jake", "type": "Snake" } 
         ] 
      } 
   ],
   
   "location": { "state": "NY", "county": "Manhattan", "city": "NY" }, 
   "isRegistered": false 
}

让我们看一个示例，在该示例中我们将创建一些简单的UDF。

以下是CreateUserDefinedFunctions的实现。

private async static Task CreateUserDefinedFunctions(DocumentClient client) { 
   Console.WriteLine(); 
   Console.WriteLine("**** Create User Defined Functions ****"); 
   Console.WriteLine();  
    
   await CreateUserDefinedFunction(client, "udfRegEx");  
}

我们有一个udfRegEx，在CreateUserDefinedFunction中，我们从本地文件中获取其JavaScript代码。我们为新的UDF构造定义对象，并使用集合的SelfLink和udfDefinition对象调用CreateUserDefinedFunctionAsync，如以下代码所示。

private async static Task
CreateUserDefinedFunction(DocumentClient client, string udfId) { 
   var udfBody = File.ReadAllText(@"..\..\Server\" + udfId + ".js"); 
    
   var udfDefinition = new UserDefinedFunction { 
      Id = udfId, 
      Body = udfBody 
   }; 
   
   var result = await client
      .CreateUserDefinedFunctionAsync(_collection.SelfLink, udfDefinition); 
   var udf = result.Resource; 
    
   Console.WriteLine("Created user defined function {0}; RID: {1}", 
      udf.Id, udf.ResourceId);  
        
   return udf; 
}

我们从结果的resource属性中获取新的UDF，并将其返回给调用方。要显示现有的UDF，下面是ViewUserDefinedFunctions的实现。我们调用CreateUserDefinedFunctionQuery并像往常一样遍历它们。

private static void ViewUserDefinedFunctions(DocumentClient client) { 
   Console.WriteLine(); 
   Console.WriteLine("**** View UDFs ****"); 
   Console.WriteLine(); 
    
   var udfs = client  
      .CreateUserDefinedFunctionQuery(_collection.UserDefinedFunctionsLink) 
      .ToList();  
        
   foreach (var udf in udfs) { 
      Console.WriteLine("User defined function {0}; RID: {1}", udf.Id, udf.ResourceId); 
   }
}

DocumentDB SQL不提供用于搜索子字符串或正则表达式的内置函数，因此以下小段代码可以弥补这一空白，它是JavaScript函数。

function udfRegEx(input, regex) { 
   return input.match(regex); 
}

给定第一个参数中的输入字符串，请使用JavaScript的内置正则表达式支持，将第二个参数中的模式匹配字符串传入。比赛。我们可以运行一个子字符串查询，以查找在其lastName属性中带有单词Andersen的所有商店。

private static void Execute_udfRegEx(DocumentClient client) { 
   var sql = "SELECT c.name FROM c WHERE udf.udfRegEx(c.lastName, 'Andersen') != null";
    
   Console.WriteLine(); 
   Console.WriteLine("Querying for Andersen"); 
    
   var documents = client.CreateDocumentQuery(_collection.SelfLink, sql).ToList();  
   Console.WriteLine("Found {0} Andersen:", documents.Count); 
    
   foreach (var document in documents) { 
      Console.WriteLine("Id: {0}, Name: {1}", document.id, document.lastName); 
   } 
}

请注意，我们必须使用前缀udf对每个UDF参考进行限定。就像任何普通查询一样，我们只是将SQL传递给CreateDocumentQuery 。最后，让我们从CreateDocumentClient任务中调用上述查询

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 = 'myfirstdb'").AsEnumerable().First();
      collection = client.CreateDocumentCollectionQuery(database.CollectionsLink, 
         "SELECT * FROM c WHERE c.id = 'Families'").AsEnumerable().First();
             
      await CreateUserDefinedFunctions(client);
   
      ViewUserDefinedFunctions(client);
   
      Execute_udfRegEx(client); 
   } 
}

执行以上代码后，将产生以下输出。

**** Create User Defined Functions ****  
Created user defined function udfRegEx; RID: kV5oANVXnwAlAAAAAAAAYA==  
**** View UDFs ****  
User defined function udfRegEx; RID: kV5oANVXnwAlAAAAAAAAYA==  
Querying for Andersen 
Found 1 Andersen: 
 Id: AndersenFamily, Name: Andersen