Initial implementation for nested property selector. Not null safe.

McRule.Tests/Filtering.cs

@@ -26,6 +26,7 @@ namespace McRule.Tests {
             public int? number { get; set; }
             public bool stillWithUs { get; set; }
             public string[] tags { get; set; }
+            public People? relatedTo {  get; set; }
 
             public People(string name, string kind, int? number, bool stillWithUs, string[] tags = null)
             {
@@ -326,6 +327,23 @@ namespace McRule.Tests {
             var failedGenerator = new FailedExpressionGeneratorBase();
             Assert.Throws<NotImplementedException>(() => { _ = eans.GeneratePredicateExpression<People>(failedGenerator); });
         }
+
+
+        [Test]
+        public void SelectPropertyOfMemberObject() {
+            var filter = vikings.GetPredicateExpression<People>()?.Compile();
+
+            // This should be the two Vikings: Lars then Ragnar, in that order
+            var folks = peoples.Where(filter).OrderBy(x => x.name);
+
+            // We specify that Lars is related to Ragnar
+            folks.First().relatedTo = folks.Skip(1).First();
+
+            var testMembersProperty = ("People", "relatedTo.name", "Ragnar").ToFilterRule().GetPredicateExpression<People>().Compile();
+
+            Assert.NotNull(folks);
+            Assert.True(testMembersProperty(folks.First()));
+        }
     }
 
     internal class FailedExpressionGeneratorBase : ExpressionGeneratorBase

McRule/PredicateExpressionPolicyExtensions.cs

@@ -91,7 +91,9 @@ public static partial class PredicateExpressionPolicyExtensions
         // Bind to the property by name and make the constant value
         // we'll be passing into the Contains() call
         var parameter = Expression.Parameter(typeof(T), "x");
-        var opLeft = Expression.Property(parameter, property);
+        Expression opLeft = parameter;
+        foreach (string p in property.Split(".")) opLeft = Expression.PropertyOrField(opLeft, p);
+
         var opRight = Expression.Constant(value);
 
         // Create generic method which is bound with the Call Expression below
@@ -281,7 +283,9 @@ public abstract class ExpressionGeneratorBase : ExpressionGenerator
     public Expression<Func<T, bool>> GetPredicateExpressionForType<T>(string property, string value)
     {
         var parameter = Expression.Parameter(typeof(T), "x");
-        var opLeft = Expression.Property(parameter, property);
+        Expression opLeft = parameter;
+        foreach (string p in property.Split(".")) opLeft = Expression.PropertyOrField(opLeft, p);
+
         (bool literalFound, LiteralValue? processedValue) = GetStringValueLiteral(value);
         var opRight = Expression.Constant(value);
         Expression? comparison = null;