Fix: negative links did not handle null correctly

src/XrmMockup365/Internal/EntityMatcher.cs

@@ -80,6 +80,8 @@ private static bool Matches(object attr, ConditionOperator op, IEnumerable<objec
                     return IsEqual(attr, values);
 
                 case ConditionOperator.NotEqual:
+                    // Dataverse excludes null-valued records for "not" conditions (NULL <> value is unknown).
+                    if (attr == null) return false;
                     return !Matches(attr, ConditionOperator.Equal, values);
 
                 case ConditionOperator.GreaterThan:
@@ -89,6 +91,7 @@ private static bool Matches(object attr, ConditionOperator op, IEnumerable<objec
                     return Compare((IComparable)attr, op, (IComparable)ValueConverter.ConvertTo(values.First(), attr?.GetType()));
 
                 case ConditionOperator.NotLike:
+                    if (attr == null) return false;
                     return !Matches(attr, ConditionOperator.Like, values);
 
                 case ConditionOperator.Like:
@@ -129,6 +132,8 @@ private static bool Matches(object attr, ConditionOperator op, IEnumerable<objec
                     return values.Contains(ValueConverter.ConvertTo(attr, values.FirstOrDefault()?.GetType()));
 
                 case ConditionOperator.NotIn:
+                    // Only exclude nulls when there are values to compare; an empty NotIn matches all rows.
+                    if (attr == null && values.Any()) return false;
                     return !Matches(attr, ConditionOperator.In, values);
 
                 case ConditionOperator.BeginsWith:
@@ -144,6 +149,7 @@ private static bool Matches(object attr, ConditionOperator op, IEnumerable<objec
                     }
 
                 case ConditionOperator.DoesNotBeginWith:
+                    if (attr == null) return false;
                     return !Matches(attr, ConditionOperator.BeginsWith, values);
 
                 case ConditionOperator.EndsWith:
@@ -159,6 +165,7 @@ private static bool Matches(object attr, ConditionOperator op, IEnumerable<objec
                     }
 
                 case ConditionOperator.DoesNotEndWith:
+                    if (attr == null) return false;
                     return !Matches(attr, ConditionOperator.EndsWith, values);
                 default:
                     throw new NotImplementedException($"The ConditionOperator '{op}' has not been implemented yet.");

tests/XrmMockup365Test/TestRetrieveMultiple.cs

@@ -1010,6 +1010,71 @@ public void TestQueryExpressionLinkEntityNoSetEntityNameAndAlias()
             Assert.Equal(2, res.Count());
         }
 
+        [Fact]
+        public void TestQueryExpressionLinkEntityNotEqualExcludesNull()
+        {
+            // lead1 (-> contact1) has Address1_PostalCode = "MK111DW"; lead2 (-> contact2) has none (null).
+            // A NotEqual link-criteria must exclude the contact whose linked lead has a null value,
+            // matching real Dataverse (NULL <> value is unknown -> row excluded).
+            var query = new QueryExpression("contact")
+            {
+                ColumnSet = new ColumnSet("lastname")
+            };
+            query.Criteria = new FilterExpression(LogicalOperator.And);
+            query.Criteria.AddCondition(new ConditionExpression("lastname", ConditionOperator.Like, "contact%"));
+
+            var linkEntity = new LinkEntity()
+            {
+                LinkToEntityName = "lead",
+                LinkToAttributeName = "parentcontactid",
+                LinkFromEntityName = "contact",
+                LinkFromAttributeName = "contactid",
+                Columns = new ColumnSet("address1_postalcode"),
+                EntityAlias = "lead"
+            };
+            linkEntity.LinkCriteria = new FilterExpression(LogicalOperator.And);
+            linkEntity.LinkCriteria.AddCondition(new ConditionExpression("lead", "address1_postalcode", ConditionOperator.NotEqual, "ZZZ"));
+            query.LinkEntities.Add(linkEntity);
+
+            var res = orgAdminService.RetrieveMultiple(query).Entities;
+            Assert.Single(res);
+            Assert.Equal("contact1", res[0].GetAttributeValue<string>("lastname"));
+        }
+
+        [Fact]
+        public void TestQueryExpressionNotEqualExcludesNull()
+        {
+            // Only lead1 has a postal code; leads 2-4 are null. NotEqual must exclude the null rows.
+            var query = new QueryExpression("lead") { ColumnSet = new ColumnSet(true) };
+            query.Criteria.AddCondition(new ConditionExpression("address1_postalcode", ConditionOperator.NotEqual, "ZZZ"));
+
+            var res = orgAdminService.RetrieveMultiple(query).Entities.Cast<Lead>().ToList();
+            Assert.Single(res);
+            Assert.Equal(lead1.Id, res[0].Id);
+        }
+
+        [Fact]
+        public void TestQueryExpressionNotInExcludesNull()
+        {
+            var query = new QueryExpression("lead") { ColumnSet = new ColumnSet(true) };
+            query.Criteria.AddCondition(new ConditionExpression("address1_postalcode", ConditionOperator.NotIn, new[] { "AAA", "BBB" }));
+
+            var res = orgAdminService.RetrieveMultiple(query).Entities.Cast<Lead>().ToList();
+            Assert.Single(res);
+            Assert.Equal(lead1.Id, res[0].Id);
+        }
+
+        [Fact]
+        public void TestQueryExpressionDoesNotBeginWithExcludesNull()
+        {
+            var query = new QueryExpression("lead") { ColumnSet = new ColumnSet(true) };
+            query.Criteria.AddCondition(new ConditionExpression("address1_postalcode", ConditionOperator.DoesNotBeginWith, "ZZ"));
+
+            var res = orgAdminService.RetrieveMultiple(query).Entities.Cast<Lead>().ToList();
+            Assert.Single(res);
+            Assert.Equal(lead1.Id, res[0].Id);
+        }
+
         [Fact]
         public void TestQueryExpressionLinkEntityNoSetEntityName()
         {