[CALCITE-4804] Support Snapshot operator serialization and deserizali…

…zation

This closes apache#2955

core/src/main/java/org/apache/calcite/rel/core/Snapshot.java

@@ -18,6 +18,7 @@
 
 import org.apache.calcite.plan.RelOptCluster;
 import org.apache.calcite.plan.RelTraitSet;
+import org.apache.calcite.rel.RelInput;
 import org.apache.calcite.rel.RelNode;
 import org.apache.calcite.rel.RelWriter;
 import org.apache.calcite.rel.SingleRel;
@@ -36,6 +37,8 @@
 import java.util.List;
 import java.util.Objects;
 
+import static java.util.Objects.requireNonNull;
+
 /**
  * Relational expression that returns the contents of a relation expression as
  * it was at a given time in the past.
@@ -56,6 +59,17 @@ public abstract class Snapshot extends SingleRel implements Hintable {
 
   //~ Constructors -----------------------------------------------------------
 
+  /**
+   * Creates a Snapshot by parsing serialized output.
+   */
+  public Snapshot(RelInput input) {
+    this(input.getCluster(),
+        input.getTraitSet(),
+        ImmutableList.of(),
+        input.getInput(),
+        requireNonNull(input.getExpression("period"), "period"));
+  }
+
   /**
    * Creates a Snapshot.
    *

core/src/main/java/org/apache/calcite/rel/logical/LogicalSnapshot.java

@@ -21,6 +21,7 @@
 import org.apache.calcite.plan.RelTraitSet;
 import org.apache.calcite.rel.RelCollationTraitDef;
 import org.apache.calcite.rel.RelDistributionTraitDef;
+import org.apache.calcite.rel.RelInput;
 import org.apache.calcite.rel.RelNode;
 import org.apache.calcite.rel.core.Snapshot;
 import org.apache.calcite.rel.hint.RelHint;
@@ -40,6 +41,14 @@
 public class LogicalSnapshot extends Snapshot {
 
   //~ Constructors -----------------------------------------------------------
+
+  /**
+   * Creates a LogicalSnapshot by parsing serialized output.
+   */
+  public LogicalSnapshot(RelInput input) {
+    super(input);
+  }
+
   /**
    * Creates a LogicalSnapshot.
    *

core/src/test/java/org/apache/calcite/plan/RelWriterTest.java

@@ -68,6 +68,7 @@
 import org.apache.calcite.util.ImmutableBitSet;
 import org.apache.calcite.util.JsonBuilder;
 import org.apache.calcite.util.TestUtil;
+import org.apache.calcite.util.TimestampString;
 
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.core.type.TypeReference;
@@ -867,6 +868,30 @@ void testAggregateWithAlias(SqlExplainFormat format) {
     assertThat(s, isLinux(expected));
   }
 
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-4804">[CALCITE-4804]
+   * Support Snapshot operator serialization and deserizalization</a>. */
+  @Test void testSnapshot() {
+    // Equivalent SQL:
+    //   SELECT *
+    //   FROM products_temporal FOR SYSTEM_TIME AS OF TIMESTAMP '2011-07-20 12:34:56'
+    final RelBuilder builder = RelBuilder.create(RelBuilderTest.config().build());
+    RelNode root =
+        builder.scan("products_temporal")
+            .snapshot(
+                builder.getRexBuilder().makeTimestampLiteral(
+                    new TimestampString("2011-07-20 12:34:56"), 0))
+            .build();
+
+    RelJsonWriter jsonWriter = new RelJsonWriter();
+    root.explain(jsonWriter);
+    String relJson = jsonWriter.asString();
+    String s = deserializeAndDumpToTextFormat(getSchema(root), relJson);
+    String expected = "LogicalSnapshot(period=[2011-07-20 12:34:56])\n"
+        + "  LogicalTableScan(table=[[scott, products_temporal]])\n";
+    assertThat(s, isLinux(expected));
+  }
+
   @Test void testDeserializeInvalidOperatorName() {
     final FrameworkConfig config = RelBuilderTest.config().build();
     final RelBuilder builder = RelBuilder.create(config);