private static Expression CheckNullInPath(
IReadOnlyList <Expression> steps,
bool canBeNull,
Expression compare,
bool ignoreLast)
{
steps = steps ?? throw new ArgumentNullException(nameof(steps));
compare = compare ?? throw new ArgumentNullException(nameof(compare));
var result = compare;
var combiner = canBeNull ? (Func <Expression, Expression, Expression>)Expression.OrElse : Expression.AndAlso;
var comparer = canBeNull ? (Func <Expression, Expression, Expression>)Expression.Equal : Expression.NotEqual;
var until = ignoreLast ? steps.Count - 1 : steps.Count;
for (var i = until - 1; i >= 0; i--)
{
var property = steps[i];
if (ComparisonBuilder.CanBeNull(property.Type))
{
result = combiner(
comparer(
property,
Expression.Constant(null, typeof(object))),
result);
}
}
return(result);
}
public Expression <Func <T, bool> > IsNullComparator <T>(ParameterExpression parameter, RsqlParser.ComparisonContext context)
{
parameter = parameter ?? throw new ArgumentNullException(nameof(parameter));
context = context ?? throw new ArgumentNullException(nameof(context));
var expressionPath = this._propertyAccessor.ParsePath(parameter, context.selector().GetText());
var value = (bool)ComparisonBuilder.GetSingleValue(typeof(bool), context);
var lastNullableExpression = expressionPath.ExpressionSteps.LastOrDefault(e => ComparisonBuilder.CanBeNull(e.Type));
if (lastNullableExpression == null)
{
// Can never be null
return(Expression.Lambda <Func <T, bool> >(Expression.Constant(!value), parameter));
}
var result = Expression.Lambda <Func <T, bool> >(
ComparisonBuilder.PathCanBeNull(
expressionPath,
Expression.Equal(
lastNullableExpression,
Expression.Constant(null, typeof(object)))),
parameter);
if (value)
{
return(result);
}
var body = Expression.Not(result.Body);
result = Expression.Lambda <Func <T, bool> >(body, parameter);
return(result);
}