[DatabaseLoader] Create higher level convenient methods for DatabaseLoader

[CESARDELATORRE]

As mentioned by Diego, these additions would help by simplifying the API usage for users even further and it should be pretty easy to implement for us: 👍

@divega commented: https://github.com/dotnet/machinelearning-samples/pull/617#pullrequestreview-284597248

@CESARDELATORRE, I did a deferred review. The experience seems pretty good.

1: And I agree with you that it could be even better with some sugar method that loads directly from the arguments of DatabaseSource.

2: I can also see other possible shortcuts of similar nature. For example, although DbProviderFactory is the all encompassing root concept if you need everything from an ADO.NET provider, a DbConnection can give you everything but DbConnectionStringBuilder, and it is a much more familiar abstraction for most users than the DbProviderFactory. So, unless you need to manipulate connection strings in a provider agnostic way (not commonly an useful thing to do), you could make the sugar Load method generic on the provider's DbConnection type. All in all, I would would love to meet with you and the devs and walk trough the product code and API. It is likely that more things like this will come up.

[Pomoinytskyi]

Hi @divega and @CESARDELATORRE

I am interested in this task. Could you please explain what sugar methods you want to have in more details? You wrote:

you could make the sugar Load method generic on the provider's DbConnection type

What providers type do you mean under

provider's DbConnection type

if I am correctly understand you, it is not the DbProviderFactory.

I can propose such methods: public static IDataView Load<TData>(this DbConnection connection, string connectionString, string query, IHostEnvironment host) or public static IDataView Load<TData>(this DatabaseSource source, string connectionString, string query, IHostEnvironment host)

Thanks.