public static T FindIn(Expression expression)
{
if (expression == null)
{
return(default(T));
}
var finder = new ConstantFinder <T>();
finder.Visit(expression);
return(finder.Result);
}
public IQueryable <TElement> CreateQuery <TElement>(Expression expression)
{
if (!(expression is MethodCallExpression mc))
{
throw new ArgumentException("Invalid expression", nameof(expression));
}
var queryable = ConstantFinder <IQueryable <TSource> > .FindIn(mc.Arguments[0]);
if (queryable == null)
{
throw new InvalidOperationException("Cannot find source.");
}
if (mc.Method.TryFindMethod(out var method))
{
var arguments = mc.Arguments.Select(x =>
LambdaFinder.FindIn(x) ?? ConstantFinder <object> .FindIn(x)).ToArray();
return((IQueryable <TElement>)method.Invoke(null, arguments));
}
var source = new Lazy <IEnumerable <TSource> >(() => (queryable as IQueryableCollection <TSource>)?.Source ?? queryable);
var collection = new Lazy <IReadOnlyObservableCollection <TSource> >(() => source.Value as IReadOnlyObservableCollection <TSource>);
var list = new Lazy <IReadOnlyObservableList <TSource> >(() => source.Value as IReadOnlyObservableList <TSource>);
switch (mc.Method.Name)
{
case "OfType" when mc.Arguments.Count == 1 && collection.Value != null:
return(list.Value != null
? new CastingReadOnlyObservableList <TSource, TElement>(list.Value.ListWhere(x => x is TElement)).AsQueryableCollection()
: new CastingReadOnlyObservableCollection <TSource, TElement>(source.Value.ListWhere(x => x is TElement)).AsQueryableCollection());
case "Cast" when mc.Arguments.Count == 1 && collection.Value != null:
return(list.Value != null
? new CastingReadOnlyObservableList <TSource, TElement>(list.Value).AsQueryableCollection()
: new CastingReadOnlyObservableCollection <TSource, TElement>(collection.Value).AsQueryableCollection());
}
var updater = new QueryModifier();
expression = updater.Visit(expression);
if (updater.Source == null)
{
throw new InvalidOperationException();
}
var result = updater.Source.Provider.CreateQuery <TElement>(expression);
return(result);
}
public TResult Execute <TResult>(Expression expression)
{
if (expression is MethodCallExpression mc)
{
if (mc.Method.TryFindMethod(out var method))
{
var arguments = mc.Arguments.Select(x =>
LambdaFinder.FindIn(x) ?? ConstantFinder <object> .FindIn(x)).ToArray();
return((TResult)method.Invoke(null, arguments));
}
}
var updater = new QueryModifier();
expression = updater.Visit(expression);
if (updater.Source == null)
{
throw new InvalidOperationException();
}
var result = updater.Source.Provider.Execute <TResult>(expression);
return(result);
}