Ordo Rule Engine Development

Core Concepts

Step Flow Model

Ordo uses Step Flow model to organize rules:

• Decision Step: Conditional judgment, jumps to different steps based on conditions
• Action Step: Execute actions (set variables, call external services)
• Terminal Step: Terminate execution, return result

RuleSet Structure

rust
1use ordo_core::prelude::*;
2
3// Create ruleset
4let mut ruleset = RuleSet::new("rule_name", "entry_step_id");
5
6// Add steps
7ruleset.add_step(step);
8
9// Validate ruleset
10ruleset.validate()?;
11
12// Execute
13let executor = RuleExecutor::new();
14let result = executor.execute(&ruleset, input)?;

Creating Steps

Decision Step

rust
1// Builder pattern
2let step = Step::decision("check_balance", "Check Balance")
3    .branch(Condition::from_string("balance >= 1000"), "approve")
4    .branch(Condition::from_string("balance >= 500"), "review")
5    .default("reject")
6    .build();

Terminal Step

rust
1let step = Step::terminal(
2    "approve",
3    "Approved",
4    TerminalResult::new("APPROVED")
5        .with_message("User has been approved")
6        .with_output("allowed", Expr::literal(true))
7        .with_output("discount", Expr::literal(0.2))
8);

Action Step

rust
1let step = Step::action("set_discount", "Set Discount")
2    .set("discount_rate", Expr::literal(0.15))
3    .set("applied_at", Expr::field("timestamp"))
4    .next("final_check")
5    .build();

Condition Expressions

Basic Comparisons

rust
1Condition::from_string("age >= 18")
2Condition::from_string("status == \"active\"")
3Condition::from_string("balance > 0")

Logical Combinations

rust
1Condition::from_string("age >= 18 && status == \"active\"")
2Condition::from_string("tier == \"gold\" || tier == \"platinum\"")
3Condition::from_string("!(is_blocked == true)")

Field Access

rust
1Condition::from_string("user.profile.level >= 5")
2Condition::from_string("items[0].price > 100")
3Condition::from_string("len(orders) > 0")

JSON/YAML Format

JSON Rule Definition

json
1{
2  "config": {
3    "name": "discount-check",
4    "version": "1.0.0",
5    "entry_step": "check_vip"
6  },
7  "steps": {
8    "check_vip": {
9      "id": "check_vip",
10      "name": "Check VIP Status",
11      "type": "decision",
12      "branches": [
13        { "condition": "user.vip == true", "next_step": "vip_discount" }
14      ],
15      "default_next": "normal_discount"
16    },
17    "vip_discount": {
18      "id": "vip_discount",
19      "name": "VIP Discount",
20      "type": "terminal",
21      "result": { "code": "VIP", "message": "20% discount" }
22    }
23  }
24}

Loading and Executing

rust
1// Load from JSON and pre-compile
2let mut ruleset = RuleSet::from_json_compiled(json_str)?;
3
4// Or step by step
5let mut ruleset = RuleSet::from_json(json_str)?;
6ruleset.compile()?;  // Pre-compile expressions
7
8// Execute
9let executor = RuleExecutor::new();
10let input: Value = serde_json::from_str(r#"{"user": {"vip": true}}"#)?;
11let result = executor.execute(&ruleset, input)?;

Configuration Options

RuleSetConfig

FieldMissingBehavior

• Lenient: Treat missing field as null
• Strict: Error on missing field
• Default: Use default value

Compiled Rules (.ordo format)

rust
1// Compile to binary format
2let compiled = RuleSetCompiler::compile(&ruleset)?;
3compiled.save_to_file("rules.ordo")?;
4
5// Load and execute
6let loaded = CompiledRuleSet::load_from_file("rules.ordo")?;
7let executor = CompiledRuleExecutor::new();
8let result = executor.execute(&loaded, input)?;

Execution Tracing

rust
1// Enable tracing
2ruleset.config.enable_trace = true;
3
4let result = executor.execute(&ruleset, input)?;
5
6// Access trace information
7if let Some(trace) = result.trace {
8    for step in trace.steps {
9        println!("Step: {} -> {}", step.step_id, step.result);
10    }
11}

Key Files

• crates/ordo-core/src/rule/model.rs - RuleSet model
• crates/ordo-core/src/rule/step.rs - Step type definitions
• crates/ordo-core/src/rule/executor.rs - Rule executor
• crates/ordo-core/src/rule/compiler.rs - Rule compiler
• crates/ordo-core/examples/basic_usage.rs - Basic example