Querying and creating document collections

The following lines declare the code for the CreateCollectionIfNotExistsAsync asynchronous static method, which creates a new document collection if a collection with id equal to the value stored in the collectionId field doesn't exist in the database. Add the following lines to the existing code of the Program.cs file. The code file for the sample is included in the learning_cosmos_db_04_01 folder in the dot_net_core_2_samples/SampleApp1/SampleApp1/Program.cs file:

private static async Task<DocumentCollection> CreateCollectionIfNotExistsAsync() 
{ 
    var databaseUri = UriFactory.CreateDatabaseUri(databaseId); 
    DocumentCollection documentCollectionResource; 
    var isCollectionCreated = await client.CreateDocumentCollectionQuery(databaseUri) 
        .Where(c => c.Id == collectionId) 
        .CountAsync() == 1; 
    if (isCollectionCreated) 
    { 
        Console.WriteLine($"The collection {collectionId} already exists."); 
   ...