In DocumentDB, we actually use SQL to query documents. If we are doing .NET development, there is also a LINQ provider that can be used and which can generate appropriate SQL from a LINQ query.

Supported Data Types

In DocumentDB, all JSON primitive types are supported in the LINQ provider included with the DocumentDB .NET SDK which are as follows −

• Numeric
• Boolean
• String
• Null

Supported Expression

The following scalar expressions are supported in the LINQ provider included with the DocumentDB .NET SDK.

• Constant Values − Includes constant values of the primitive data types.

• Property/Array Index Expressions − Expressions refer to the property of an object or an array element.

• Arithmetic Expressions − Includes common arithmetic expressions on numerical and Boolean values.

• String Comparison Expression − Includes comparing a string value to some constant string value.

• Object/Array Creation Expression − Returns an object of compound value type or anonymous type or an array of such objects. These values can be nested.

Supported LINQ Operators

Here is a list of supported LINQ operators in the LINQ provider included with the DocumentDB .NET SDK.

• Select − Projections translate to the SQL SELECT including object construction.

• Where − Filters translate to the SQL WHERE, and support translation between && , || and ! to the SQL operators.

• SelectMany − Allows unwinding of arrays to the SQL JOIN clause. Can be used to chain/nest expressions to filter array elements.

• OrderBy and OrderByDescending − Translates to ORDER BY ascending/descending.

• CompareTo − Translates to range comparisons. Commonly used for strings since they’re not comparable in .NET.

• Take − Translates to the SQL TOP for limiting results from a query.

• Math Functions − Supports translation from .NET’s Abs, Acos, Asin, Atan, Ceiling, Cos, Exp, Floor, Log, Log10, Pow, Round, Sign, Sin, Sqrt, Tan, Truncate to the equivalent SQL built-in functions.

• String Functions − Supports translation from .NET’s Concat, Contains, EndsWith, IndexOf, Count, ToLower, TrimStart, Replace, Reverse, TrimEnd, StartsWith, SubString, ToUpper to the equivalent SQL built-in functions.

• Array Functions − Supports translation from .NET’s Concat, Contains, and Count to the equivalent SQL built-in functions.

• Geospatial Extension Functions − Supports translation from stub methods Distance, Within, IsValid, and IsValidDetailed to the equivalent SQL built-in functions.

• User-Defined Extension Function − Supports translation from the stub method UserDefinedFunctionProvider.Invoke to the corresponding user-defined function.

• Miscellaneous − Supports translation of coalesce and conditional operators. Can translate Contains to String CONTAINS, ARRAY_CONTAINS or the SQL IN depending on context.

Let’s take a look at an example where we will be using the .Net SDK. Following are the three documents which we will be consider for this example.

New Customer 1

{ 
   "name": "New Customer 1", 
   "address": { 
      "addressType": "Main Office", 
      "addressLine1": "123 Main Street", 
		
      "location": { 
         "city": "Brooklyn", 
         "stateProvinceName": "New York" 
      },
	  
      "postalCode": "11229", 
      "countryRegionName": "United States" 
   }, 
}

New Customer 2

{ 
   "name": "New Customer 2", 
	
   "address": {
      "addressType": "Main Office", 
      "addressLine1": "678 Main Street", 
		
      "location": { 
         "city": "London", 
         "stateProvinceName": " London " 
      }, 
	  
      "postalCode": "11229", 
      "countryRegionName": "United Kingdom" 
   }, 
}

New Customer 3

{ 
   "name": "New Customer 3", 
	
   "address": { 
      "addressType": "Main Office", 
      "addressLine1": "12 Main Street", 
		
      "location": { 
         "city": "Brooklyn", 
         "stateProvinceName": "New York" 
      },
	  
      "postalCode": "11229", 
      "countryRegionName": "United States" 
   },
}

Following is the code in which we query using LINQ. We”ve defined a LINQ query in q, but it won”t execute until we run .ToList on it.

private static void QueryDocumentsWithLinq(DocumentClient client) { 
   Console.WriteLine(); 
   Console.WriteLine("**** Query Documents (LINQ) ****"); 
   Console.WriteLine();  
   Console.WriteLine("Quering for US customers (LINQ)"); 
   var q = 
      from d in client.CreateDocumentQuery<Customer>(collection.DocumentsLink) 
      where d.Address.CountryRegionName == "United States" 
		
   select new { 
      Id = d.Id, 
      Name = d.Name, 
      City = d.Address.Location.City 
   };
   
   var documents = q.ToList();  
   Console.WriteLine("Found {0} US customers", documents.Count); 
	
   foreach (var document in documents) { 
      var d = document as dynamic; 
      Console.WriteLine(" Id: {0}; Name: {1}; City: {2}", d.Id, d.Name, d.City); 
   }
   
   Console.WriteLine(); 
}

The SDK will convert our LINQ query into SQL syntax for DocumentDB, generating a SELECT and WHERE clause based on our LINQ syntax.

Let’s call the above queries from the CreateDocumentClient task.

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 = ''MyCollection''").AsEnumerable().First();  
      QueryDocumentsWithLinq(client); 
   } 
}

When the above code is executed, it produces the following output.

**** Query Documents (LINQ) **** 
 
Quering for US customers (LINQ) 
Found 2 US customers 
   Id: 7e9ad4fa-c432-4d1a-b120-58fd7113609f; Name: New Customer 1; City: Brooklyn 
   Id: 34e9873a-94c8-4720-9146-d63fb7840fad; Name: New Customer 1; City: Brooklyn