Rule Expressions and short circuit evaluation

[bmasotta-lcg]

I found that for the following expression, the engine tries to evaluate the entire expression instead of performing a short circuit evaluation. Is this by design?

Expression:
"input1.falseProp == true AND input1.missingProp"

Error Returned:
"Exception while parsing expression input1.falseProp == true AND input1.missingProp - Operator 'AND' incompatible with operand types 'Boolean' and 'Object'"

InputMessage:
{
"testInputName": "shortCircuitMissingProperty",
"falseProp": false
}

notice there's no "missingProp" property in input1 message
My idea is to handle different input message types (schemas) with several rules, all in the same workflow, by filtering by a message property:

input1.telemetryType == 'weather' AND input1.windSpeed > 100
...
input1.telemetryType == 'tracker' AND input1.motorCurrent > 5

Thanks a lot!

[bmasotta-lcg]

also I was looking to be able to handle short circuit evaluation by using nested rules and the OrElse operator...
but is not working for me
having two child rules with a different custom action each one, both custom actions gets executed, no matter if the first one is true, the second one also gets evaluated...

[abbasc52]

@bmasotta-lcg Short circuiting using nested rules works only if you enable perf mode in ReSettings. You can refer this example.

RulesEngine/test/RulesEngine.UnitTest/NestedRulesTest.cs

Lines 21 to 65 in 7b4e45d

	[InlineData(NestedRuleExecutionMode.All)]
	[InlineData(NestedRuleExecutionMode.Performance)]
	public async Task NestedRulesShouldFollowExecutionMode(NestedRuleExecutionMode mode)
	{
	var workflow = GetWorkflow();
	var reSettings = new ReSettings { NestedRuleExecutionMode = mode };
	var rulesEngine = new RulesEngine(workflow, reSettings: reSettings);
	dynamic input1 = new ExpandoObject();
	input1.trueValue = true;
	List<RuleResultTree> result = await rulesEngine.ExecuteAllRulesAsync("NestedRulesTest", input1);
	var andResults = result.Where(c => c.Rule.Operator == "And").ToList();
	var orResults = result.Where(c => c.Rule.Operator == "Or").ToList();
	Assert.All(andResults,
	c => Assert.False(c.IsSuccess)
	);
	Assert.All(orResults,
	c => Assert.True(c.IsSuccess));
	if (mode == NestedRuleExecutionMode.All)
	{
	Assert.All(andResults,
	c => Assert.Equal(c.Rule.Rules.Count(), c.ChildResults.Count()));
	Assert.All(orResults,
	c => Assert.Equal(c.Rule.Rules.Count(), c.ChildResults.Count()));
	}
	else if (mode == NestedRuleExecutionMode.Performance)
	{
	Assert.All(andResults,
	c => {
	Assert.Equal(c.IsSuccess, c.ChildResults.Last().IsSuccess);
	Assert.Single(c.ChildResults.Where(d => c.IsSuccess == d.IsSuccess));
	Assert.True(c.ChildResults.SkipLast(1).All(d => d.IsSuccess == true));
	});
	Assert.All(orResults,
	c => {
	Assert.Equal(c.IsSuccess, c.ChildResults.Last().IsSuccess);
	Assert.Single(c.ChildResults.Where(d => c.IsSuccess == d.IsSuccess));
	Assert.True(c.ChildResults.SkipLast(1).All(d => d.IsSuccess == false));
	});
	}

Also, on your earlier question, if you could provide me more details on how you are passing the input (and the type of it). I might be able to help you better.

[bmasotta]

thanks @abbasc52 . I was able to implement sce by using nested rules. Also found it's working with static types but not dynamic type.
I need to investigate a little more. But it's weird, when using dynamic type all the IEnumerable logic is lost (I think it's related to the linq expression library implementation)

e.g: if I use static type collection methods in a CustomType (e.g.: IEnumerable GetTelemetry()) there's no problem in using expressions as .Count(). Select(x=> and so on)
but if I switch to dynamic types (e.g.: IEnumerable GetTelemetry() ) I start to experience problems.

the thing is that for IoT solutions is very appreciated to be able to handle dynamic types (changin schemas) in a natural way

[bmasotta-lcg]

I was unable to handle missing or null values on dynamic types without using nested rules or separate workflows.
I created a sample repository showing this.
https://github.com/bmasotta-lcg/RulesEngineNullShortCircuit

While I create rules that look for always-present properties on dynamic type inputs I don't have any problem (that's similar to work with static types)

But if I need to work with dynamic or changing schemas in dynamic input messages and test for null on a specific field value, by using any kind of short circuit evaluation method, the RulesEngine will raise an error related to the expression evaluation.

  "Expression": "input1.value != null && input1.value == 10",

},
"ExceptionMessage": "Exception while parsing expression "input1.value != null && input1.value == 10" - The binary operator Equal is not defined for the types \u0027System.Object\u0027 and \u0027System.Int32\u0027."

"Expression": "input1.value != null AndAlso input1.value == 10",
"ExceptionMessage": "Exception while parsing expression \u0060input1.value != null AndAlso input1.value == 10\u0060 - The binary operator Equal is not defined for the types \u0027System.Object\u0027 and \u0027System.Int32\u0027."

(https://dynamic-linq.net/advanced-null-propagation)
"Expression": "np(input1.value, 0) == 10",
"ExceptionMessage": "Exception while parsing expression \u0060input1.value != null \u0026\u0026 input1.value == 10\u0060 - The binary operator Equal is not defined for the types \u0027System.Object\u0027 and \u0027System.Int32\u0027."

"Expression": "(input1.value == null ? 0 : input1.value) == 10",
"ExceptionMessage": "Exception while parsing expression \u0060(input1.value == null ? 0 : input1.value) == 10\u0060 - The binary operator Equal is not defined for the types \u0027System.Object\u0027 and \u0027System.Int32\u0027."

One thing to add is that I find very confusing mentioning in the readme file that the rule expressions are similar to regular c# lambda expression. This is not true. The RulesEngine is silently using the https://dynamic-linq.net library, a library that looks like official .NET due to the namespace it uses, but it has it's own syntax, not the same syntax as for lamba expressions

[SolzIT]

Any updates on this error. In my case I always have the attribute but it is either null or has a integer value. For whatever methods I try I am getting the same error

The binary operator Equal is not defined for the types System.Object and System.Int32."