Updated BigQuery expression capabilities

Author: fernst

src/main/java/io/cdap/plugin/gcp/bigquery/relational/SQLExpressionFactory.java

@@ -1,5 +1,6 @@
 package io.cdap.plugin.gcp.bigquery.relational;
 
+import io.cdap.cdap.etl.api.engine.sql.StandardSQLCapabilities;
 import io.cdap.cdap.etl.api.relational.Capability;
 import io.cdap.cdap.etl.api.relational.CoreExpressionCapabilities;
 import io.cdap.cdap.etl.api.relational.Expression;
@@ -12,7 +13,7 @@
 import io.cdap.cdap.etl.api.relational.StringExpressionFactoryType;
 import io.cdap.plugin.gcp.bigquery.sqlengine.builder.BigQueryBaseSQLBuilder;
 
-import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
 
@@ -22,6 +23,15 @@
  */
 public class SQLExpressionFactory implements ExpressionFactory<String> {
 
+  private static final Set<Capability> CAPABILITIES = Collections.unmodifiableSet(
+    new HashSet<Capability>() {{
+      add(StringExpressionFactoryType.SQL);
+      add(StandardSQLCapabilities.BIGQUERY);
+      add(CoreExpressionCapabilities.CAN_GET_QUALIFIED_DATASET_NAME);
+      add(CoreExpressionCapabilities.CAN_GET_QUALIFIED_COLUMN_NAME);
+      add(CoreExpressionCapabilities.CAN_SET_DATASET_ALIAS);
+    }});
+
   /**
    * Gets the expression factory type, which in this case is SQL.
    *
@@ -46,19 +56,17 @@ public Expression compile(String expression) {
   /**
    * Get the set of Capabilities supported, which in this case is SQL.
    *
-   * @return A single capability, {@link StringExpressionFactoryType}.SQL.
+   * @return a set containing all capabilities supported by this SQL engine.
    */
   @Override
   public Set<Capability> getCapabilities() {
-    return new HashSet<>(Arrays.asList(StringExpressionFactoryType.SQL,
-                                       CoreExpressionCapabilities.CAN_GET_QUALIFIED_DATASET_NAME,
-                                       CoreExpressionCapabilities.CAN_GET_QUALIFIED_COLUMN_NAME,
-                                       CoreExpressionCapabilities.CAN_SET_DATASET_ALIAS));
+    return CAPABILITIES;
   }
 
   /**
    * Returns qualified dataset name for an expression. For BigQuery, dataset names are wrapped in quotes (`).
    * The resulting expression will be invalid if the relation is not a {@link BigQueryRelation}.
+   *
    * @param relation supplied relation.
    * @return valid containing the column name wrapped in quotes; or invalid expression.
    */
@@ -78,8 +86,9 @@ public ExtractableExpression<String> getQualifiedDataSetName(Relation relation)
    * Returns qualified dataset column for a column. For BigQuery, dataset names are wrapped in quotes (`).
    * The resulting expression will be invalid if the relation is not a {@link BigQueryRelation}
    * or the column does not exist in this relation.
+   *
    * @param relation supplied relation.
-   * @param column column name.
+   * @param column   column name.
    * @return valid containing the column name wrapped in quotes; or invalid expression.
    */
   @Override
@@ -111,6 +120,7 @@ public Relation setDataSetAlias(Relation relation, String alias) {    // Ensure
 
   /**
    * Method used to build a qualified identified in BigQuery
+   *
    * @param identifier identifier
    * @return Identifier wrapped in quotes (`)
    */