/// <summary>
/// Analyses the provided expression and returns a DeferTransformation instance containing
/// information necessary to defer execution of expressions identified as unsuitable by the
/// supplied IExpressionAnalyser
/// </summary>
/// <param name="expression">The LINQ query expression to be analysed</param>
/// <param name="analyserFactory">A factory lambda used to retrieve an instance of the desired IExpressionAnalyser</param>
/// <returns>The results of the transformation process</returns>
public static DeferTransformation Transform(Expression expression, Func <IExpressionAnalyser> analyserFactory)
{
var analyser = analyserFactory();
var instance = new DeferExpressionTransformer(analyser);
instance._transformation.TransformedExpression = instance.Visit(expression);
return(instance._transformation);
}
/// <summary>
/// Wraps and executes the supplied expression.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="expression"></param>
/// <returns></returns>
public IEnumerator <T> ExecuteQuery <T>(Expression expression)
{
// transform the expression into the intermediate query, building the transformation
// object at the same time for postprocessing
var transformation = DeferExpressionTransformer.Transform(expression, _config.AnalyserFactory);
// create the inner query, which produces the intermediate objects
var createQueryMethod = typeof(IQueryProvider).GetGenericMethod("CreateQuery", BindingFlags.Instance | BindingFlags.Public, new[] { transformation.IntermediateItemType }, new[] { typeof(Expression) });
var intermediateQuery = createQueryMethod.Invoke(_innerProvider, new object[] { transformation.TransformedExpression });
// get the enumerator for the results of the inner query
var enumerableType = typeof(IEnumerable <>).MakeGenericType(transformation.IntermediateItemType);
var getEnumeratorMethod = enumerableType.GetMethod("GetEnumerator");
var intermediateEnumerator = getEnumeratorMethod.Invoke(intermediateQuery, new object[] { });
// wrap the inner enumerator with our post-processing enumerator and we're done
var postProcessEnumerator = new DeferPostProcessEnumerator <T>((IEnumerator)intermediateEnumerator, transformation.PostProcessLambda);
return(postProcessEnumerator);
}
