Paging with CosmosClient in CosmosDB

Question

I'm trying to implement paging using the SDK v3 CosmosClient instead of the old DocumentClient.

Reason for this is it seems DocumentClient doesn't translate LINQ queries that contains spatial functions very well (ie: When using Within() I'll get an error from DocumentClient stating the methods is not implemented).

Paging works well with DocumentClient.CreateDocumentQuery<T> as such:

var query = DocumentClient.CreateDocumentQuery<T>(UriFactory.CreateDocumentCollectionUri("master", "features"), feedOptions)
                .Where(t => t.Type == typeof(T).Name)
                .Where(pred)
                .AsDocumentQuery();

string queryContinuationToken = null;
var page = await query.ExecuteNextAsync<T>();
if (query.HasMoreResults)
    queryContinuationToken = page.ResponseContinuation;

I'm at a little loss as to where to gather a continuation token using CosmosClient and its Container class:

QueryRequestOptions options = new QueryRequestOptions();
options.MaxItemCount = maxRecords;

FeedIterator<T> feed;

if (continuationToken == "")
    feed = Container.GetItemLinqQueryable<T>(true, null, options).Where(x => x.Type == typeof(T).Name).Where(pred).ToFeedIterator();
else
    feed = Container.GetItemLinqQueryable<T>(true, continuationToken, options).Where(x => x.Type == typeof(T).Name).Where(pred).ToFeedIterator();

FeedIterator seems to have some of the members IDocumentQuery has (like HasMoreResults) but I can't find a continuation token anywhere.

What am I missing?

Answer 1

Alright, here's a Where method I implemented. Seems to work at first glance.

If you do var f = feed.ReadNextAsync() you won't get an object that's of type FeedResponse, preventing you access to the token. You need to declare f explicitly of type FeedResponse<T>

public async Task<(IEnumerable<T> Results, string ContinuationToken)> Where<T>(Expression<Func<T, bool>> pred, int maxRecords = 0, string partitionKey = "", string continuationToken = "") where T : IDocumentModel
{

    QueryRequestOptions options = new QueryRequestOptions();

    if (partitionKey != "")
        options.PartitionKey = new PartitionKey(partitionKey);


    if (maxRecords == 0)
    {
        return (Container.GetItemLinqQueryable<T>(true, null, options).Where(x => x.Type == typeof(T).Name).Where(pred), "");
    }
    else
    {
        options.MaxItemCount = maxRecords;
        string token = "";
        FeedIterator<T> feed;
        List<T> res = new List<T>();

        if (continuationToken == "")
            feed = Container.GetItemLinqQueryable<T>(true, null, options).Where(x => x.Type == typeof(T).Name).Where(pred).ToFeedIterator();
        else
            feed = Container.GetItemLinqQueryable<T>(true, continuationToken, options).Where(x => x.Type == typeof(T).Name).Where(pred).ToFeedIterator();

        Microsoft.Azure.Cosmos.FeedResponse<T> f = await feed.ReadNextAsync();
        token = f.ContinuationToken;

        foreach (var item in f)
        {
            res.Add(item);
        }

        return (res, token);
    }

}