/// <summary>
/// Map to a <see cref="IQueryable{T}"/> from the received <see cref="DbContext"/>.
/// Use the <see cref="DbContext.Set{TEntity}"/> method to select the appropriate
/// <see cref="IQueryable{TEntity}"/>.
/// </summary>
/// <typeparam name="TSource">The type of the value.</typeparam>
/// <typeparam name="TTarget">The type of the resulting queryable.</typeparam>
/// <param name="observable">The parent observable.</param>
/// <param name="mapping">The mapping function</param>
/// <returns>An instance of <see cref="IProviderObservable{TSource}"/>.</returns>
public static IProviderObservable <IQueryable <TTarget> > MapToQueryable <TSource, TTarget>(
this IProviderObservable <TSource> observable,
Func <DbContext, IQueryable <TTarget> > mapping)
where TSource : class =>
observable.MapToQueryable((s, c) => mapping(c));
