@alcaeus Can you confirm that this is the right thing to do?

I see why not defining the authSource might make sense.
Yet, the official Docker image seems to hardcode the authentication database to be admin (according to their Docker Hub doc and the entrypoint) so maybe we could define it when we detected some credentials to make it a smooth experience for most users?

Regarding the main database I'm not sure to understand why we should not define it. Because if I get that correctly this means this will make any user of mongodb required to explicitly specify it in Doctrine's configuration, right?

I think it might also be interesting to ping @quentint who initially contributed the addition of the MONGODB_URL definition :)

👋 @alcaeus is on holiday so @GromNaN summoned me instead.

Consider a Docker Compose configuration for a MongoDB service as follows...

What is the purpose of MONGO_INITDB_DATABASE in the Docker Compose configuration if it's not utilized for the authentication database? Is that meant to be a default database for the application to use? If so, does that mean Docker always creates users in the admin database (perhaps so according to docker-entrypoint.sh, which @tucksaun shared).

In MongoDB connection strings, specifying a default working database in the URL path (e.g., mongodb://user:pass@127.0.0.1:27017/defaultDb) uses defaultDb as both the default and authentication database.

With respect to the PHP driver, there is no notion of a "default database" and it'd be helpful to only consider an "auth database" (with preference given to the authSource URI option over the "path" component in the URI. The MongoDB Connection String spec is the authority here.

That said, some other drivers/libraries may still infer a default database from the "path" component in the URI (see mongodb/mongo-php-driver#1470 (comment) for more context on that); however, this isn't relevant to Doctrine ODM.

According to DoctrineMongoDBExtension::loadConnections(), the server property for a connection is only used to construct the PHP library's MongoDB\Client object. The connection string seems entirely unrelated to any default database utilized for Doctrine ODM models.

In the absence of specifying a database name in the model metadata, ODM relies on Configuration::getDefaultDB(), and falls back to 'doctrine' (see: DocumentManager::getDocumentDatabase()). When using the Symfony bundle, Configuration::setDefaultDB() should always be called with something. If the application doesn't explicitly define default_database in the bundle config, the DIC configuration uses 'default' (see: Configuration::getConfigTreeBuilder()).

Yet, the official Docker image seems to hardcode the authentication database to be admin (according to their Docker Hub doc and the entrypoint) so maybe we could define it when we detected some credentials to make it a smooth experience for most users?

I see no reason to specify 'admin' as a default value, as drivers already use that as a default for database-related auth mechanisms (see: MongoDB Auth spec. Note that other auth mechanisms might use a different value (e.g. $external), but I expect those wouldn't come up with the Docker container being used here.

Some other thoughts:

I don't understand what the isMaster() function (called just above the diff in this PR) does. The function dates back to the first commit for envs.go in 5ac4bd9 and originally applied to pgsql, mysql, and mongodb schemes. It was later removed for pgsql and mysql in 1c0b3c8 but remains in place for MongoDB.

I also don't understand what the other environment variables are used for. MONGO_NAME, MONGO_DATABASE, and MONGO_DB are all still set to endpoint["path"]. Since we previously established that the "path" URI component is not a default database but merely a deprecated way of specifying the auth databsae, I wouldn't expect it to be used for any other purpose. And even if it was desirable to expose the "path" as an environment variable, assigning it to three different vars seems redundant and more likely to mislead users. This question relates more to the paste that @malhusseiny included in #451.

Going back to my original question about MONGO_INITDB_DATABASE in the Docker config. Perhaps that would be a sensible value to use for one of these other environment variables (if it is accessible within envs.go). If MONGO_INITDB_DATABASE is intended to be the application database, Symfony users would likely want to use the same value for the default_database option in the DoctrineMongoDBBundle config.