[GitHub] [drill] arina-ielchiieva commented on a change in pull request #1797: DRILL-7278: Refactor result set loader projection mechanism

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arina-ielchiieva commented on a change in pull request #1797: DRILL-7278: 
Refactor result set loader projection mechanism
URL: https://github.com/apache/drill/pull/1797#discussion_r289938524
 
 

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 File path: 
exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/scan/project/projSet/ProjectionSetBuilder.java
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 @@ -0,0 +1,101 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.drill.exec.physical.impl.scan.project.projSet;
+
+import java.util.Collection;
+
+import org.apache.drill.common.exceptions.CustomErrorContext;
+import org.apache.drill.common.expression.SchemaPath;
+import org.apache.drill.exec.physical.rowSet.ProjectionSet;
+import org.apache.drill.exec.physical.rowSet.project.RequestedTuple;
+import 
org.apache.drill.exec.physical.rowSet.project.RequestedTuple.TupleProjectionType;
+import org.apache.drill.exec.physical.rowSet.project.RequestedTupleImpl;
+import org.apache.drill.exec.record.metadata.TupleMetadata;
+
+public class ProjectionSetBuilder {
+
+  private RequestedTuple parsedProjection;
+  private TypeConverter typeConverter;
+  private CustomErrorContext errorContext;
+
+  /**
+   * Record (batch) readers often read a subset of available table columns,
+   * but want to use a writer schema that includes all columns for ease of
+   * writing. (For example, a CSV reader must read all columns, even if the 
user
+   * wants a subset. The unwanted columns are simply discarded.)
+   * <p>
+   * This option provides a projection list, in the form of column names, for
+   * those columns which are to be projected. Only those columns will be
+   * backed by value vectors; non-projected columns will be backed by "null"
+   * writers that discard all values.
+   *
+   * @param projection the list of projected columns
+   * @return this builder
+   */
+
+  public ProjectionSetBuilder projectionList(Collection<SchemaPath> 
projection) {
+    if (projection == null) {
+      parsedProjection = null;
+    } else {
+      parsedProjection = RequestedTupleImpl.parse(projection);
+    }
+    return this;
+  }
+
+  public ProjectionSetBuilder parsedProjection(RequestedTuple projection) {
+    parsedProjection = projection;
+    return this;
+  }
+
+  public ProjectionSetBuilder outputSchema(TupleMetadata schema) {
+    typeConverter = TypeConverter.builder().providedSchema(schema).build();
+    return this;
+  }
+
+  public ProjectionSetBuilder typeConverter(TypeConverter converter) {
+    this.typeConverter = converter;
+    return this;
+  }
+
+  public ProjectionSetBuilder errorContext(CustomErrorContext errorContext) {
+    this.errorContext = errorContext;
+    return this;
+  }
+
+  public ProjectionSet build() {
+    TupleProjectionType projType = parsedProjection == null ?
+        TupleProjectionType.ALL : parsedProjection.type();
+
+    ProjectionSet projSet;
+    switch (projType) {
+    case ALL:
+      projSet = new WildcardProjectionSet(typeConverter);
+      break;
+    case NONE:
+      projSet = ProjectionSetFactory.projectNone();
+      break;
+    case SOME:
+      projSet =  new ExplicitProjectionSet(parsedProjection, typeConverter);
 
 Review comment:
   ```suggestion
         projSet = new ExplicitProjectionSet(parsedProjection, typeConverter);
   ```

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