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Mongodb – How to use Dependency Injection (.net8) to Inject two MongoBb Clients

How do I use Dependency Injection (.net8) to Inject two MongoBb Clients? I have a scenario where I need to read from Db1/collection1 and then save something to Db2/collection2. In my startup I have the following but not sure how to inject a second IMongoClient (both have different connection string)

services.AddSingleton<IMongoClient>x => new
    MongoClient(My_Server_Connection1));

services.AddSingleton<IMongoClient>x => new
    MongoClient(My_Server_Connection2));

I would like to be able to do something like this in my DataStore constructor

Db DataStore 1:

public DataStore1(IMongoClient clientWithConStr1, IMongoClient clientWithConStr2)
{
    database1 = clientWithConStr1.GetDatabase(DatabaseName1);
    database2 = clientWithConStr2.GetDatabase(DatabaseName1);
}
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2

Answers


  1. 0

    MongoClient instance is not restricted to use a single database or collection which means that you can operate with as many dbs/collections as you want with a single client. So, I see no reasons to have dedicated instance in your case.

    Also, even though you create a 2 different MongoClient variables like:

    var inst1 = new MongoClient(); 
var inst2 = new MongoClient();
// inst1 == inst2;

    effectively it will be still a single instance as long as provided connection strings are the same. See my answer here for details.

    Don’t forget that when you create a mongo client, you effectively create a few background threads and some other shared resources like connection pool which, in turns, holds opened sockets, session pool and so on, so it’s heavy operation and it’s a good idea to reuse it.

    However, if you really want to distinguish these clients, configure ApplicationName option in MongoClientSettings or connectionString.

    UPDATE: If your question is only DI related, then consider Keyed service dependency injection, see this article:

    var builder = WebApplication.CreateBuilder(args);
builder.Services.AddKeyedSingleton<IMongoClient, MongoClient>("connection1");
builder.Services.AddKeyedSingleton<IMongoClient, MongoClient>("connection2");

    Consuming:

    public class Connection1Wrapper([FromKeyedServices("connection1")] IMongoClient client)
{
    public string SomeWork(string message) => client.#some work#;
}
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  2. 0

    For your scenario to handle multiple MongoClients with different connection strings, it is better to implement a factory to select the MongoClient (provider) by type.

    1. An interface and class provider to initiate and retrive the MongoClient by type.
    public interface IMongoClientProvider
{
    public int Type { get; }

    public IMongoClient GetMongoClient();
}

public class MongoClientProvider : IMongoClientProvider
{
    public int Type { get; init; }
    private readonly IMongoClient _client;

    public MongoClientProvider(int type, string connectionString)
    {
        Type = type;
        _client = new MongoClient(connectionString);
    }

    public IMongoClient GetMongoClient()
    {
        return _client;
    }
}
    1. A factory to select the MongoClientProvider by type`.
    using System.Collections.Generic;
using System.Linq;

public class MongoClientFactory
{
    private readonly IEnumerable<IMongoClientProvider> _providers;

    public MongoClientFactory(IEnumerable<IMongoClientProvider> providers)
    {
        _providers = providers;
    }

    public MongoClient GetMongoClient(int type)
    {
        var provider = _providers.SingleOrDefault(x => x.Type == type);
        if (provider == null)
        {
            throw new Exception("Unsupported type for provider.");
        }

        return provider.GetMongoClient();
    }
}
    1. Register the MongoClientProvider and MongoClientFactory into DI container.
    services.AddSingleton<IMongoClientProvider>(new MongoClientProvider(1, My_Server_Connection));
services.AddSingleton<IMongoClientProvider>(new MongoClientProvider(2, My_Server_Connection2));

services.AddSingleton<MongoClientFactory>();
    1. In the DataStore class, get the MongoClientFactory from the DI and retrieve the MongoClient instance by type.
    public class DataStore1
{
    private readonly IMongoDatabase database;
    private readonly string databaseName = "DatabaseName1";
    
    public DataStore1(MongoClientFactory factory)
    {
        var client = factory.GetMongoClient(1);
        database = client.GetDatabase(databaseName);
    }
}

public class DataStore2
{
    private readonly IMongoDatabase database;
    private readonly string databaseName = "DatabaseName2";
    
    public DataStore2(MongoClientFactory factory)
    {
        var client = factory.GetMongoClient(2);
        database = client.GetDatabase(databaseName);
    }
}
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