I was trying to delete a document in DocumentDB / CosmoDB and I was surprised to be faced with the error message of, ‘PartitionKey value must be supplied’. There doesn’t appear to be a way of passing the partition key to DeleteDocumentAsync. The trick is to use the request options. For example, if your collection is partitioned by ProductID;

await this.documentClient.DeleteDocumentAsync(productDocument._self, new RequestOptions { PartitionKey = new Microsoft.Azure.Documents.PartitionKey(productDocument.ProductID) });