wrangler sql execution initial setup

wrangler-api/src/main/java/io/cdap/wrangler/api/Directive.java

@@ -16,6 +16,8 @@
 
 package io.cdap.wrangler.api;
 
+import io.cdap.cdap.etl.api.relational.Relation;
+import io.cdap.cdap.etl.api.relational.RelationalTranformContext;
 import io.cdap.wrangler.api.parser.UsageDefinition;
 
 import java.util.List;
@@ -51,7 +53,8 @@
  *   }
  * </code>
  */
-public interface Directive extends Executor<List<Row>, List<Row>>, EntityMetrics {
+public interface Directive extends Executor<List<Row>, List<Row>>, EntityMetrics,
+    DirectiveRelationalTransform {
   /**
    * This defines a interface variable that is static and final for specify
    * the {@code type} of the plugin this interface would provide.
@@ -126,4 +129,11 @@ default List<EntityCountMetric> getCountMetrics() {
     // no op
     return null;
   }
+
+  @Override
+  default Relation transform(RelationalTranformContext relationalTranformContext,
+      Relation relation) {
+    // no-op
+    return relation;
+  }
 }

wrangler-api/src/main/java/io/cdap/wrangler/api/DirectiveRelationalTransform.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright © 2023 Cask Data, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package io.cdap.wrangler.api;
+
+import io.cdap.cdap.etl.api.relational.InvalidRelation;
+import io.cdap.cdap.etl.api.relational.LinearRelationalTransform;
+import io.cdap.cdap.etl.api.relational.Relation;
+import io.cdap.cdap.etl.api.relational.RelationalTranformContext;
+
+/**
+ * {@link DirectiveRelationalTransform} provides relational transform support for
+ * wrangler directives.
+ */
+public interface DirectiveRelationalTransform extends LinearRelationalTransform {
+
+  /**
+   * Implementation of linear relational transform for each supported directive.
+   *
+   * @param relationalTranformContext transformation context with engine, input and output parameters
+   * @param relation input relation upon which the transformation is applied.
+   * @return transformed relation as the output relation. By default, returns an Invalid relation
+   * for unsupported directives.
+   */
+  default Relation transform(RelationalTranformContext relationalTranformContext,
+      Relation relation) {
+    return new InvalidRelation("SQL execution for the directive is currently not supported.");
+  }
+
+  /**
+   * Indicates whether the directive is supported by relational transformation or not.
+   *
+   * @return boolean value for the directive SQL support.
+   * By default, returns false, indicating that the directive is currently not supported.
+   */
+  default boolean isSQLSupported() {
+    return false;
+  }
+
+}

wrangler-core/src/main/java/io/cdap/directives/column/Drop.java

@@ -19,6 +19,8 @@
 import io.cdap.cdap.api.annotation.Description;
 import io.cdap.cdap.api.annotation.Name;
 import io.cdap.cdap.api.annotation.Plugin;
+import io.cdap.cdap.etl.api.relational.Relation;
+import io.cdap.cdap.etl.api.relational.RelationalTranformContext;
 import io.cdap.wrangler.api.Arguments;
 import io.cdap.wrangler.api.Directive;
 import io.cdap.wrangler.api.DirectiveExecutionException;
@@ -88,4 +90,18 @@ public Mutation lineage() {
       .drop(Many.of(columns))
       .build();
   }
+
+  @Override
+  public Relation transform(RelationalTranformContext relationalTranformContext,
+      Relation relation) {
+    for (String col: columns) {
+      relation = relation.dropColumn(col);
+    }
+    return relation;
+  }
+
+  @Override
+  public boolean isSQLSupported() {
+    return true;
+  }
 }

wrangler-core/src/main/java/io/cdap/wrangler/utils/SqlExpressionGenerator.java

@@ -0,0 +1,34 @@
+/*
+ *  Copyright © 2023 Cask Data, Inc.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ *  use this file except in compliance with the License. You may obtain a copy of
+ *  the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ *  License for the specific language governing permissions and limitations under
+ *  the License.
+ */
+
+package io.cdap.wrangler.utils;
+
+import io.cdap.cdap.etl.api.relational.Expression;
+import io.cdap.cdap.etl.api.relational.ExpressionFactory;
+import io.cdap.cdap.etl.api.relational.RelationalTranformContext;
+import io.cdap.cdap.etl.api.relational.StringExpressionFactoryType;
+
+import java.util.Optional;
+
+/**
+ * Utility class that contains methods for sql expression generation.
+ */
+public class SqlExpressionGenerator {
+
+  public static Optional<ExpressionFactory<String>> getExpressionFactory(RelationalTranformContext ctx) {
+    return ctx.getEngine().getExpressionFactory(StringExpressionFactoryType.SQL);
+  }
+}