如何从 Cosmos DB 中过滤的 FeedIterator 获取总数

Question

I have the following code to filter some data in a Cosmos DB:

Container container = await service.GetContainer(containerName, partitionKeyA);
using (FeedIterator<T> resultSet = container.GetItemQueryIterator<T>(
    queryDefinition: GetComplexSQLQueryDefinition(),
    paginationInfo.Token,
    requestOptions: new QueryRequestOptions()
    {
      PartitionKey = new PartitionKey(partitionKey),
      MaxItemCount = 10
    }
    ))
{ 
  FeedResponse<T> response = await resultSet.ReadNextAsync();
  //get total count
  int totalCount = -1;
}

The query can yield many records, hence I need the pagination .

Unfortunately I need the total count of the items - and it can vary according to the filtering.

According to this answer , I have only 2 options:

1. I create a second SQL query that uses an SQL select command to count the records - then query the database again to select the actual records:

    var query = new QueryDefinition("SELECT value count(1) FROM c WHERE c.tenantId = @type"); query.WithParameter("@type", '5d484526d76e9653e6226aa2'); var container = client.GetContainer("DatabaseName", "CollectionName"); var iterator = container.GetItemQueryIterator<int>(query); var count = 0; while (iterator.HasMoreResults) { var currentResultSet = await iterator.ReadNextAsync(); foreach (var res in currentResultSet) { count += res; } } Console.WriterLine($"The first count is: {count}");

2. I translate my complex SQL query to LINQ and use its Count method:

   //should be formatted as code

   var count = container.GetItemLinqQueryable(true).Count(item => item.tenantId.Equals('5d484526d76e9653e6226aa2'));

Both seems quite cumbersome for such a simple task so I wonder if there is any better or more effective approach.

What else could I try?

Answer 1

Here's roughly the code I've used to perform count operations with .NET SDK v3 based on an arbitrary QueryDefinition . There are a few aspects not shown like the full logic of deserialization with System.Text.Json, but hopefully the gist comes across. The idea is to provide a query with base:

SELECT VALUE COUNT(1) FROM c

To get a single document as result which contains the result count;

public async Task<int?> CountAsync(QueryDefinition query, string partitionKey)
{
    var options = new QueryRequestOptions() { PartitionKey = new(partitionKey), MaxItemCount = 1 };
    int? count = null;
    using var resultSet = cosmosService.DataContainer.GetItemQueryStreamIterator(query, requestOptions: options);
    while (resultSet.HasMoreResults)
    {
        using var response = await resultSet.ReadNextAsync();
        if (response.IsSuccessStatusCode)
        {
            // Deserialize response into CosmosResponse<int>
            var deserializeResult = await FromJsonStream<CosmosResponse<int>>(response.Content);
            if (!deserializeResult.HasSuccessValue(out CosmosResponse<int>? responseContent))
            {
                return null; // Or some failure
            }

            if (responseContent.Documents.Any())
            {
                count = responseContent.Documents[0];
                break;
            }
            else
            {
                return null;// Or some failure
            }
        }
        else // Unexpected status. Abort processing.
        {
            return null;// Or some failure
        }
    }

    return count;
}

Helper class to deserialize the response:

public class CosmosResponse<T>
{
    [JsonPropertyName("Documents")]
    public IReadOnlyList<T> Documents { get; set; } = Array.Empty<T>();

    [JsonPropertyName("_count")]
    public int Count { get; set; }
}