[FIXED] MAUI Blazor App can't connect to MongoDB Atlas via ConnectionString, why?

Issue

I coded a MAUI Blazor App which connects to MongoDB Atlas and loads some Data in the App. Everything works fine if I run the App on a Windows PC. But if I compile/run the same code on an Android device I get this error in the development tools:

 **blazor.webview.js:1 List of configured name servers must not be empty. (Parameter 'servers')**
   at DnsClient.LookupClient.QueryInternal(DnsQuestion question, DnsQuerySettings queryOptions, IReadOnlyCollection`1 servers)
   at DnsClient.LookupClient.Query(DnsQuestion question)
   at DnsClient.LookupClient.Query(String query, QueryType queryType, QueryClass queryClass)
   at MongoDB.Driver.Core.Misc.DnsClientWrapper.ResolveTxtRecords(String domainName, CancellationToken cancellationToken)
   at MongoDB.Driver.Core.Configuration.ConnectionString.Resolve(Boolean resolveHosts, CancellationToken cancellationToken)
   at MongoDB.Driver.MongoUrl.Resolve(Boolean resolveHosts, CancellationToken cancellationToken)
   at MongoDB.Driver.MongoClientSettings.FromUrl(MongoUrl url)
   at MongoDB.Driver.MongoClientSettings.FromConnectionString(String connectionString)
   at MongoDB.Driver.MongoClient..ctor(String connectionString)
   at MBz_MauiAndMongoDb.Pages.Index.OnInitializedAsync() in **C:\Users\XXX\source\repos\MBz_MauiAndMongoDb\MBz_MauiAndMongoDb\Pages\Index.razor:line 23
   at Microsoft.AspNetCore.Components.ComponentBase.RunInitAndSetParametersAsync()**

The error occures at is moment:

var client = new MongoClient(MongoDbConnectionString);
var db = client.GetDatabase(MongoDbName);

The ConnectionString works perfect if run on a Windows maschine. The ConnectionString looks like this:

"mongodb+srv://AtlasUser: myUserName+myCluster/test?retryWrites=true&w=majority&ssl=true"

I use the MongoDB.Bson and the C# MongoDB.Driver.

In the Documentations I only find the connectionString Syntax I use. But that seems to NOT work with MAUI App on a Android-Device! If I just use "mongodb://AtlasUser:..." without the 'srv' I get a timeout error. Or is it a problem with permissions under Android, I didn't change the original MAUI Blazor template stuff in that regard. Any Ideas?

Thx for your Help!

Solution

It's simple: on WebAssembly you cannot do something impossible to do using JavaScript in a browser.

The mongodb:// protocol is a TCP based protocol and cannot be connected from any kind of code running in a browser. This limitation is not specific to Blazor.. any other WebAssembly like Uno Platform will have the exact same limitations.

You have 2 options to circumvent this:

1. You connect to a server part of your application using http/https (it could be REST API, WebSockets, SignalR or whatever else running on http) and, from there, you connect to the MongoDB server.
2. You connect directly to the MongoDB server using a REST interface -- but I'm pretty sure the MongoDB.Driver won't be able to use them and you'll have to build your queries by yourself.

Disclamer: I'm a senior architect at Uno Platform working on the WebAssembly platform.

Answered By - Carl de Billy
Answer Checked By - Dawn Plyler (JavaFixing Volunteer)