Treat empty _in arrays as false, ie.

Author: u12206050

src/BccCode.Linq/Server/Filter.cs

@@ -112,10 +112,12 @@ private void _parse(string json)
             else if (new[] { "_in", "_nin" }.Contains(key))
             {
                 var array = JsonConvert.DeserializeObject<T[]>(value.ToString() ?? string.Empty);
-                if (array is null || array.Length == 0)
+                // Treat empty arrays as a valid value (resulting in a predicate that's always false for _in
+                // and always true for _nin). Only null is considered invalid.
+                if (array is null)
                 {
                     throw new ArgumentException(
-                        $"JSON filter rule is invalid. Array under {key} is null or empty.");
+                        $"JSON filter rule is invalid. Array under {key} is null.");
                 }
 
                 deserializedJson[key] = array;
@@ -135,12 +137,19 @@ private void _parse(string json)
                     ? typeof(ValueTuple<,>).MakeGenericType(propertyType, propertyType)
                     : typeof(Tuple<,>).MakeGenericType(propertyType, propertyType);
 
-                deserializedJson[key] = Activator.CreateInstance(tupleType,
+                var tupleInstance = Activator.CreateInstance(tupleType,
                     OperandToExpressionResolver.ConvertValue(propertyInfo?.PropertyType ?? GetFilterType(),
                         array[0].ToString()),
                     OperandToExpressionResolver.ConvertValue(propertyInfo?.PropertyType ?? GetFilterType(),
                         array[1].ToString())
                 );
+                
+                if (tupleInstance == null)
+                {
+                    throw new InvalidOperationException($"Failed to create tuple instance for key {key}");
+                }
+                
+                deserializedJson[key] = tupleInstance;
             }
             else if (key.StartsWith("_"))
             {

tests/BccCode.Linq.Tests/FilterTests.cs

@@ -77,11 +77,12 @@ public void should_cast_value_to_decimal_list()
     }
 
     [Fact]
-    public void should_throw_exception_on_empty_list()
+    public void should_allow_empty_list_in_in_operator()
     {
         var json = @"{ ""StringArrayProp"": { ""_in"": [] } }";
 
-        Assert.Throws<ArgumentException>(() => new Filter<TestClass>(json));
+        var ex = Record.Exception(() => new Filter<TestClass>(json));
+        Assert.Null(ex);
     }
 
     [Fact]

tests/BccCode.Linq.Tests/Server/FilterToLambdaParserTests.cs

@@ -111,4 +111,41 @@ public void should_get_correct_result_when_filtering_nested_object()
 
         Assert.Equal(expected.Count, result.Count);
     }
+
+    [Fact]
+    public void should_match_using_in_operator()
+    {
+        var jsonRule = "{\n  \"country\": { \n    \"_in\": [\"Poland\", \"Greece\"]\n  }\n}";
+
+        var expected = PeopleList.Where(person => new[] { "Poland", "Greece" }.Contains(person.Country)).ToList();
+        var f = new Filter<Person>(jsonRule);
+        var exp = FilterToLambdaParser.Parse(f);
+        var result = PeopleList.Where(exp.Compile()).ToList();
+
+        Assert.Equal(expected.Count, result.Count);
+    }
+
+    [Fact]
+    public void empty_in_array_should_match_no_items()
+    {
+        var jsonRule = "{\n  \"country\": { \n    \"_in\": []\n  }\n}";
+
+        var f = new Filter<Person>(jsonRule);
+        var exp = FilterToLambdaParser.Parse(f);
+        var result = PeopleList.Where(exp.Compile()).ToList();
+
+        Assert.Empty(result);
+    }
+
+    [Fact]
+    public void empty_nin_array_should_match_all_items()
+    {
+        var jsonRule = "{\n  \"country\": { \n    \"_nin\": []\n  }\n}";
+
+        var f = new Filter<Person>(jsonRule);
+        var exp = FilterToLambdaParser.Parse(f);
+        var result = PeopleList.Where(exp.Compile()).ToList();
+
+        Assert.Equal(PeopleList.Count, result.Count);
+    }
 }