/// <remarks>
/// This is the entry point to the expression compilation system. The system
/// a) Will rewrite the expression to avoid null refs when any part of the expression tree is evaluated to null
/// b) Attempt to cache the result, or an intermediate part of the result.
/// If the provided expression is particularly obscure and the system doesn't know how to handle it, it will
/// return null.
/// </remarks>
/// <returns>
/// FROM: https://github.com/dotnet/aspnetcore/blob/v3.1.11/src/Mvc/Mvc.ViewFeatures/src/CachedExpressionCompiler.cs
/// </returns>
public static Func <TModel, object> Process <TModel, TResult>(
Expression <Func <TModel, TResult> > expression)
{
if (expression == null)
{
throw new ArgumentNullException(nameof(expression));
}
return(CachedExpressionCompiler.Process(expression));
}
private static void InsertIndexerInvocationText(
StringBuilder builder,
Expression indexExpression,
LambdaExpression parentExpression)
{
if (builder == null)
{
throw new ArgumentNullException(nameof(builder));
}
if (indexExpression == null)
{
throw new ArgumentNullException(nameof(indexExpression));
}
if (parentExpression == null)
{
throw new ArgumentNullException(nameof(parentExpression));
}
if (parentExpression.Parameters == null)
{
throw new ArgumentException(string.Format("The '{0}' property of '{1}' must not be null.",
nameof(parentExpression.Parameters),
nameof(parentExpression)));
}
var converted = Expression.Convert(indexExpression, typeof(object));
var fakeParameter = Expression.Parameter(typeof(object), null);
var lambda = Expression.Lambda <Func <object, object> >(converted, fakeParameter);
Func <object, object> func;
try
{
func = CachedExpressionCompiler.Process(lambda) ?? lambda.Compile();
}
catch (InvalidOperationException ex)
{
var parameters = parentExpression.Parameters.ToArray();
throw new InvalidOperationException(
string.Format("The expression compiler was unable to evaluate the indexer expression '{0}' because it references the model parameter '{1}' which is unavailable.",
indexExpression, parameters[0].Name),
ex);
}
builder.Insert(0, ']');
builder.Insert(0, Convert.ToString(func(null), CultureInfo.InvariantCulture));
builder.Insert(0, '[');
}
