chore: cleaned up code and added docs

Author: GurtejSohi

document-store/src/integrationTest/java/org/hypertrace/core/documentstore/DocStoreQueryV1Test.java

@@ -3508,9 +3508,7 @@ SELECT item, MAX(date) AS latest_date
     */
     Query subQuery =
         Query.builder()
-            .addSelection(
-                SelectionSpec.of(
-                    IdentifierExpression.of("item")))
+            .addSelection(SelectionSpec.of(IdentifierExpression.of("item")))
             .addSelection(
                 SelectionSpec.of(
                     AggregateExpression.of(
@@ -3541,14 +3539,14 @@ SELECT item, MAX(date) AS latest_date
                         RelationalOperator.EQ,
                         AliasedIdentifierExpression.builder()
                             .name("item")
-                            .alias("latest")
+                            .contextAlias("latest")
                             .build()),
                     RelationalExpression.of(
                         IdentifierExpression.of("date"),
                         RelationalOperator.EQ,
                         AliasedIdentifierExpression.builder()
                             .name("latest_date")
-                            .alias("latest")
+                            .contextAlias("latest")
                             .build())))
             .build();
 

document-store/src/main/java/org/hypertrace/core/documentstore/expression/impl/AliasedIdentifierExpression.java

@@ -5,17 +5,28 @@
 import org.hypertrace.core.documentstore.parser.SelectTypeExpressionVisitor;
 
 /**
- * Expression representing an identifier/column name with an alias
+ * Expression for referencing an identifier/column name within a context having an alias.
  *
- * <p>Example: AliasedIdentifierExpression.of("col1", "col1_alias");
+ * <p>Example: In this query: <code>
+ *     SELECT item, quantity, date
+ *     FROM <implicit_collection>
+ *     JOIN (
+ *         SELECT item, MAX(date) AS latest_date
+ *         FROM <implicit_collection>
+ *         GROUP BY item
+ *     ) AS latest
+ *     ON item = latest.item
+ *     ORDER BY `item` ASC;
+ * </code> the rhs of the join condition "latest.item" can be expressed as: <code>
+ *  AliasedIdentifierExpression.builder().name("item").alias("alias1").build() </code>
  */
 @Value
 public class AliasedIdentifierExpression extends IdentifierExpression {
-  String alias;
+  String contextAlias;
 
-  private AliasedIdentifierExpression(final String name, final String alias) {
+  private AliasedIdentifierExpression(final String name, final String contextAlias) {
     super(name);
-    this.alias = alias;
+    this.contextAlias = contextAlias;
   }
 
   @Override
@@ -25,7 +36,7 @@ public <T> T accept(final SelectTypeExpressionVisitor visitor) {
 
   @Override
   public String toString() {
-    return "`" + getAlias() + "." + getName() + "`";
+    return "`" + getContextAlias() + "." + getName() + "`";
   }
 
   public static AliasedIdentifierExpressionBuilder builder() {
@@ -34,24 +45,25 @@ public static AliasedIdentifierExpressionBuilder builder() {
 
   public static class AliasedIdentifierExpressionBuilder {
     private String name;
-    private String alias;
+    private String contextAlias;
 
     public AliasedIdentifierExpressionBuilder name(final String name) {
       this.name = name;
       return this;
     }
 
-    public AliasedIdentifierExpressionBuilder alias(final String alias) {
-      this.alias = alias;
+    public AliasedIdentifierExpressionBuilder contextAlias(final String contextAlias) {
+      this.contextAlias = contextAlias;
       return this;
     }
 
     public AliasedIdentifierExpression build() {
       Preconditions.checkArgument(
           this.name != null && !this.name.isBlank(), "name is null or blank");
       Preconditions.checkArgument(
-          this.alias != null && !this.alias.isBlank(), "alias is null or blank");
-      return new AliasedIdentifierExpression(this.name, this.alias);
+          this.contextAlias != null && !this.contextAlias.isBlank(),
+          "contextAlias is null or blank");
+      return new AliasedIdentifierExpression(this.name, this.contextAlias);
     }
   }
 }

document-store/src/main/java/org/hypertrace/core/documentstore/expression/impl/SubQueryJoinExpression.java

@@ -12,6 +12,9 @@
 /**
  * Expression representing a join operation where the right side expression is a subquery. Note that
  * this currently supports a self-join only, so the collection to be joined with is implicit.
+ *
+ * <p>For an example of using this expression, see the testSelfJoinWithSubQuery method in
+ * DocStoreQueryV1Test.
  */
 @Value
 @Builder(toBuilder = true)

document-store/src/main/java/org/hypertrace/core/documentstore/mongo/query/parser/MongoAliasedIdentifierExpressionParser.java

@@ -2,18 +2,15 @@
 
 import lombok.NoArgsConstructor;
 import org.hypertrace.core.documentstore.expression.impl.AliasedIdentifierExpression;
+import org.hypertrace.core.documentstore.mongo.MongoUtils;
 
 @NoArgsConstructor
 public final class MongoAliasedIdentifierExpressionParser extends MongoSelectTypeExpressionParser {
 
-  MongoAliasedIdentifierExpressionParser(final MongoSelectTypeExpressionParser baseParser) {
-    super(baseParser);
-  }
-
   @SuppressWarnings("unchecked")
   @Override
   public String visit(final AliasedIdentifierExpression expression) {
-    return "$" + parse(expression);
+    return MongoUtils.PREFIX + parse(expression);
   }
 
   String parse(final AliasedIdentifierExpression expression) {

document-store/src/main/java/org/hypertrace/core/documentstore/mongo/query/parser/MongoLetClauseBuilder.java

@@ -96,7 +96,7 @@ public BasicDBObject visit(DocumentArrayFilterExpression expression) {
   private BasicDBObject createLetClause(
       AliasedIdentifierExpression aliasedExpression, String subQueryAlias) {
     BasicDBObject letClause = new BasicDBObject();
-    if (aliasedExpression.getAlias().equals(subQueryAlias)) {
+    if (aliasedExpression.getContextAlias().equals(subQueryAlias)) {
       letClause.put(aliasedExpression.getName(), "$" + aliasedExpression.getName());
     }
     return letClause;

document-store/src/main/java/org/hypertrace/core/documentstore/mongo/query/parser/filter/MongoRelationalFilterParserFactory.java

@@ -24,7 +24,6 @@ class MongoRelationalFilterContext {
 
     @Default FilterLocation location = OUTSIDE_EXPR;
     @Default MongoSelectTypeExpressionParser lhsParser = new MongoIdentifierExpressionParser();
-    // FIXME: how to parse AliasedIdentifierExpression / IdentifierExpression in rhs?
     @Default MongoSelectTypeExpressionParser rhsParser = new MongoConstantExpressionParser();
   }
 

document-store/src/main/java/org/hypertrace/core/documentstore/parser/FromTypeExpressionVisitor.java

@@ -6,6 +6,9 @@
 public interface FromTypeExpressionVisitor {
   <T> T visit(UnnestExpression unnestExpression);
 
+  /*
+   * Subquery join expression is not supported by default. Override this method to support it.
+   */
   default <T> T visit(SubQueryJoinExpression subQueryJoinExpression) {
     throw new UnsupportedOperationException("This operation is not supported");
   }