How to correctly get all Items from DocumentDB via webapi

Question

I have the following DocumentDB Repository helper class

using Microsoft.Azure.Documents;
using Microsoft.Azure.Documents.Client;
using Microsoft.Azure.Documents.Linq;
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Linq;
using System.Linq.Expressions;
using System.Threading.Tasks;
using System.Web;

namespace TenantManagementWebApi.DataAccess
{
    public static class DocumentDBRepository<T> where T : class
    {
        private static readonly string DatabaseId = ConfigurationManager.AppSettings["database"];
        private static readonly string CollectionId = ConfigurationManager.AppSettings["collection"];
        private static DocumentClient client;

        public static async Task<T> GetItemAsync(string id)
        {
            try
            {
                Document document = await client.ReadDocumentAsync(UriFactory.CreateDocumentUri(DatabaseId, CollectionId, id));
                return (T)(dynamic)document;
            }
            catch (DocumentClientException e)
            {
                if (e.StatusCode == System.Net.HttpStatusCode.NotFound)
                {
                    return null;
                }
                else
                {
                    throw;
                }
            }
        }

        public static async Task<IEnumerable<T>> GetItemsAsync(Expression<Func<T, bool>> predicate)
        {
            IDocumentQuery<T> query = client.CreateDocumentQuery<T>(
                UriFactory.CreateDocumentCollectionUri(DatabaseId, CollectionId),
                new FeedOptions { MaxItemCount = -1 })
                .Where(predicate)
                .AsDocumentQuery();

            List<T> results = new List<T>();
            while (query.HasMoreResults)
            {
                results.AddRange(await query.ExecuteNextAsync<T>());
            }

            return results;
        }

        public static async Task<Document> CreateItemAsync(T item)
        {
            return await client.CreateDocumentAsync(UriFactory.CreateDocumentCollectionUri(DatabaseId, CollectionId), item);
        }

        public static async Task<Document> UpdateItemAsync(string id, T item)
        {
            return await client.ReplaceDocumentAsync(UriFactory.CreateDocumentUri(DatabaseId, CollectionId, id), item);
        }

        public static async Task DeleteItemAsync(string id)
        {
            await client.DeleteDocumentAsync(UriFactory.CreateDocumentUri(DatabaseId, CollectionId, id));
        }

        public static void Initialize()
        {
            client = new DocumentClient(new Uri(ConfigurationManager.AppSettings["endpoint"]), ConfigurationManager.AppSettings["authKey"]);
            CreateDatabaseIfNotExistsAsync().Wait();
            CreateCollectionIfNotExistsAsync().Wait();
        }

        private static async Task CreateDatabaseIfNotExistsAsync()
        {
            try
            {
                await client.ReadDatabaseAsync(UriFactory.CreateDatabaseUri(DatabaseId));
            }
            catch (DocumentClientException e)
            {
                if (e.StatusCode == System.Net.HttpStatusCode.NotFound)
                {
                    await client.CreateDatabaseAsync(new Database { Id = DatabaseId });
                }
                else
                {
                    throw;
                }
            }
        }

        private static async Task CreateCollectionIfNotExistsAsync()
        {
            try
            {
                await client.ReadDocumentCollectionAsync(UriFactory.CreateDocumentCollectionUri(DatabaseId, CollectionId));
            }
            catch (DocumentClientException e)
            {
                if (e.StatusCode == System.Net.HttpStatusCode.NotFound)
                {
                    await client.CreateDocumentCollectionAsync(
                        UriFactory.CreateDatabaseUri(DatabaseId),
                        new DocumentCollection { Id = CollectionId },
                        new RequestOptions { OfferThroughput = 1000 });
                }
                else
                {
                    throw;
                }
            }
        }
    }
}

And I need to do the webapi crud controller for one entity:

 public class Tenant
    {
        public string TenantId { get; set; }
        public string TenantUrl { get; set; }
        public string CertificatePath { get; set; }
        public string CertificatePassword { get; set; }

        public override string ToString()
        {
            return JsonConvert.SerializeObject(this);
        }
    }

I am not sure what to put in the Predicate to get all items which Are Tenant.

 public async Task<List<Tenant>> GetTenants()
        {
            return await  DocumentDBRepository<List<Tenant>>.GetItemsAsync(d => d. != null);
        }

Answer 1

You need to make your generic T object more specific. Limit it to a class that implements an interface of some sort like ICosmosEntity and add a EntityType property on that interface.

Then make your DTOs implement that interface and set the EntityType to the class name. That way you are able to create a dynamic predicate that gets nameof(T) and automatically adds it in the Where clause of your LINQ query.

If you just wanna get all the items in the collection then in your code the x => true predicate will do that but it won't limit it in tenants unless the collection only has tenant objects in it.

Also ReadDocumentAsync will only worth that way when your collection has no partition key (which is not really recommended)

It might worth taking a look at Cosmonaut as it does exactly what you want and more. It supports the exact same collection sharing logic that you are trying to code.

Disclaimer, I am the creator of Cosmonaut.