feat: initial subquery support (#37)

Co-authored-by: Suriya Kandaswamy <[email protected]>
Co-authored-by: Suriya Kandaswamy <[email protected]>

datafusion-federation/src/lib.rs

@@ -4,16 +4,50 @@ use std::{
     sync::Arc,
 };
 
-use datafusion::optimizer::analyzer::Analyzer;
+use datafusion::{
+    execution::context::{SessionContext, SessionState},
+    optimizer::{optimizer::Optimizer, OptimizerRule},
+};
 
-mod analyzer;
-pub use analyzer::*;
+mod optimizer;
+pub use optimizer::*;
 mod table_provider;
 pub use table_provider::*;
 
 mod plan_node;
 pub use plan_node::*;
 
+pub fn default_session_state() -> SessionState {
+    let df_state = SessionContext::new().state();
+
+    let rules = default_optimizer_rules();
+    df_state
+        .with_optimizer_rules(rules)
+        .with_query_planner(Arc::new(FederatedQueryPlanner::new()))
+}
+
+pub fn default_optimizer_rules() -> Vec<Arc<dyn OptimizerRule + Send + Sync>> {
+    // Get the default optimizer
+    let df_default = Optimizer::new();
+    let mut default_rules = df_default.rules;
+
+    // Insert the FederationOptimizerRule after the ScalarSubqueryToJoin.
+    // This ensures ScalarSubquery are replaced before we try to federate.
+    let Some(pos) = default_rules
+        .iter()
+        .position(|x| x.name() == "scalar_subquery_to_join")
+    else {
+        panic!("Could not locate ScalarSubqueryToJoin");
+    };
+
+    // TODO: check if we should allow other optimizers to run before the federation rule.
+
+    let federation_rule = Arc::new(FederationOptimizerRule::new());
+    default_rules.insert(pos + 1, federation_rule);
+
+    default_rules
+}
+
 pub type FederationProviderRef = Arc<dyn FederationProvider>;
 pub trait FederationProvider: Send + Sync {
     // Returns the name of the provider, used for comparison.
@@ -23,9 +57,9 @@ pub trait FederationProvider: Send + Sync {
     // will execute a query. For example: database instance & catalog.
     fn compute_context(&self) -> Option<String>;
 
-    // Returns an analyzer that can cut out part of the plan
+    // Returns an optimizer that can cut out part of the plan
     // to federate it.
-    fn analyzer(&self) -> Option<Arc<Analyzer>>;
+    fn optimizer(&self) -> Option<Arc<Optimizer>>;
 }
 
 impl fmt::Display for dyn FederationProvider {