feat(isthmus): add method to convert Plan into SQL strings using dialect (#704)

This PR adds a convenience function for translating a Substrait `Plan`
to a list of SQL strings in a given Calcite `SqlDialect`.

Signed-off-by: Niels Pardon <par@zurich.ibm.com>

Author: nielspardon

examples/isthmus-api/src/main/java/io/substrait/examples/ToSql.java

@@ -1,18 +1,13 @@
 package io.substrait.examples;
 
 import io.substrait.examples.IsthmusAppExamples.Action;
-import io.substrait.extension.DefaultExtensionCatalog;
-import io.substrait.extension.SimpleExtension;
-import io.substrait.isthmus.SubstraitToCalcite;
-import io.substrait.isthmus.SubstraitTypeSystem;
+import io.substrait.isthmus.SubstraitToSql;
 import io.substrait.plan.Plan;
 import io.substrait.plan.PlanProtoConverter;
 import io.substrait.plan.ProtoPlanConverter;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Paths;
-import org.apache.calcite.jdbc.JavaTypeFactoryImpl;
-import org.apache.calcite.rel.rel2sql.RelToSqlConverter;
 import org.apache.calcite.sql.SqlDialect;
 
 /**
@@ -50,28 +45,15 @@ public void run(String[] args) {
       final io.substrait.proto.Plan protoPlan = planToProto.toProto(substraitPlan);
       System.out.println(protoPlan);
 
-      final SimpleExtension.ExtensionCollection extensions =
-          DefaultExtensionCatalog.DEFAULT_COLLECTION;
-      final SubstraitToCalcite converter =
-          new SubstraitToCalcite(
-              extensions, new JavaTypeFactoryImpl(SubstraitTypeSystem.TYPE_SYSTEM));
-
       // Determine which SQL Dialect we want the converted queries to be in
       final SqlDialect sqlDialect = SqlDialect.DatabaseProduct.MYSQL.getDialect();
 
-      // Create the Sql to Calcite Relation Parser
-      final RelToSqlConverter relToSql = new RelToSqlConverter(sqlDialect);
+      SubstraitToSql substraitToSql = new SubstraitToSql();
 
       System.out.println("\n");
 
       // Convert each of the Substrait plan roots to SQL
-      substraitPlan.getRoots().stream()
-          // Substrait -> Calcite Rel
-          .map(root -> converter.convert(root).project(true))
-          // Calcite Rel -> Calcite SQL
-          .map(calciteRelNode -> relToSql.visitRoot(calciteRelNode).asStatement())
-          // Calcite SQL -> SQL String
-          .map(sqlNode -> sqlNode.toSqlString(sqlDialect).getSql())
+      substraitToSql.convert(substraitPlan, sqlDialect).stream()
           .forEachOrdered(System.out::println);
 
     } catch (IOException e) {

isthmus/src/main/java/io/substrait/isthmus/SubstraitToSql.java

@@ -1,22 +1,55 @@
 package io.substrait.isthmus;
 
 import io.substrait.extension.SimpleExtension;
+import io.substrait.plan.Plan;
+import io.substrait.plan.Plan.Root;
 import io.substrait.relation.Rel;
+import java.util.ArrayList;
+import java.util.List;
 import org.apache.calcite.prepare.Prepare;
 import org.apache.calcite.rel.RelNode;
+import org.apache.calcite.rel.rel2sql.RelToSqlConverter;
+import org.apache.calcite.sql.SqlDialect;
 
 public class SubstraitToSql extends SqlConverterBase {
 
+  protected SubstraitToCalcite substraitToCalcite;
+
   public SubstraitToSql() {
     super(FEATURES_DEFAULT);
   }
 
   public SubstraitToSql(SimpleExtension.ExtensionCollection extensions) {
     super(FEATURES_DEFAULT, extensions);
+
+    substraitToCalcite = new SubstraitToCalcite(extensions, factory);
   }
 
   public RelNode substraitRelToCalciteRel(Rel relRoot, Prepare.CatalogReader catalog) {
     return SubstraitRelNodeConverter.convert(
         relRoot, relOptCluster, catalog, parserConfig, extensionCollection);
   }
+
+  /**
+   * Converts a Substrait {@link Plan} to a list of SQL strings in the given {@link SqlDialect}.
+   *
+   * @param plan the Substrait {@link Plan} to convert to SQL, must not be null
+   * @param dialect the {@link SqlDialect} to generate the SQL strings for, must not be null
+   * @return list containing a SQL string for each {@link Plan.Root} in {@code plan}
+   */
+  public List<String> convert(Plan plan, SqlDialect dialect) {
+    List<String> result = new ArrayList<>();
+    RelToSqlConverter relToSql = new RelToSqlConverter(dialect);
+
+    for (Root root : plan.getRoots()) {
+      result.add(
+          relToSql
+              .visitRoot(substraitToCalcite.convert(root).project(true))
+              .asStatement()
+              .toSqlString(dialect)
+              .getSql());
+    }
+
+    return result;
+  }
 }