How to implement a rule engine?

Question

I have a db table that stores the following:

RuleID  objectProperty ComparisonOperator  TargetValue
1       age            'greater_than'             15
2       username       'equal'             'some_name'
3       tags           'hasAtLeastOne'     'some_tag some_tag2'

Now say I have a collection of these rules:

List rules = db.GetRules();

Now I have an instance of a user also:

User user = db.GetUser(....);

How would I loop through these rules, and apply the logic and perform the comparisons etc?

if(user.age > 15)

if(user.username == "some_name")

Since the object's property like 'age' or 'user_name' is stored in the table, along with the comparison operater 'great_than' and 'equal', how could I possible do this?

C# is a statically typed language, so not sure how to go forward.

user_4382557 · Answer

I have created a package for a rich and high performance rule engine written in dotnet, check out this repo for more info. Once installed, you can use it as simple as:

var engine = new RulesService(new RulesCompiler(), new LazyCache.Mocks.MockCachingService());
            
    var matchingRules = engine.GetMatchingRules(
        new TestModel { NumericField = 5 },
        new[] {
            new RulesConfig {
                Id = Guid.NewGuid(),
                RulesOperator = Rule.InterRuleOperatorType.And,
                RulesGroups = new RulesGroup[] {
                    new RulesGroup {
                        RulesOperator = Rule.InterRuleOperatorType.And,
                        Rules = new[] {
                            new Rule { 
                            ComparisonOperator = Rule.ComparisonOperatorType.Equal,
                            ComparisonValue = 5.ToString(),
                            ComparisonPredicate = nameof(TestModel.NumericField) 
                            }
                        }
                    }
                }
            }
        });

user_1123146 · Answer

I want to add Microsoft's Rules Engine library for future visits;

https://github.com/microsoft/RulesEngine

How to implement a rule engine?

12 Answers