/// <summary>
/// Asynchronously returns a projected document matching the filter condition.
/// </summary>
/// <typeparam name="TDocument">The type representing a Document.</typeparam>
/// <typeparam name="TKey">The type of the primary key for a Document.</typeparam>
/// <typeparam name="TProjection">The type representing the model you want to project to.</typeparam>
/// <param name="filter">A LINQ expression filter.</param>
/// <param name="projection">The projection expression.</param>
/// <param name="partitionKey">An optional partition key.</param>
public virtual async Task <TProjection> ProjectOneAsync <TDocument, TProjection, TKey>(Expression <Func <TDocument, bool> > filter, Expression <Func <TDocument, TProjection> > projection, string partitionKey = null)
where TDocument : IDocument <TKey>
where TKey : IEquatable <TKey>
where TProjection : class
{
return(await MongoDbReader.ProjectOneAsync <TDocument, TProjection, TKey>(filter, projection, partitionKey));
}