Issue #398: Fix small overhead added during the refactoirng (#436)

* Fix QbeastStats serialization/deserialization

core/src/main/scala/io/qbeast/core/model/QbeastStats.scala

@@ -19,4 +19,4 @@ case class QbeastStats(
     numRecords: Long,
     minValues: Map[String, String],
     maxValues: Map[String, String],
-    nullCount: Map[String, Int])
+    nullCount: Map[String, String])

delta/src/main/scala/io/qbeast/spark/delta/DeltaMetadataWriter.scala

@@ -20,6 +20,7 @@ import io.qbeast.core.model.IndexFile
 import io.qbeast.core.model.PreCommitHook
 import io.qbeast.core.model.PreCommitHook.PreCommitHookOutput
 import io.qbeast.core.model.QTableID
+import io.qbeast.core.model.QbeastFile
 import io.qbeast.core.model.QbeastHookLoader
 import io.qbeast.core.model.RevisionID
 import io.qbeast.core.model.TableChanges
@@ -151,10 +152,9 @@ private[delta] case class DeltaMetadataWriter(
    * @return
    *   A Map[String, String] representing the combined outputs of all hooks.
    */
-  private def runPreCommitHooks(actions: Seq[Action]): PreCommitHookOutput = {
-    val qbeastActions = actions.map(DeltaQbeastFileUtils.fromAction)
+  private def runPreCommitHooks(actions: Seq[QbeastFile]): PreCommitHookOutput = {
     preCommitHooks.foldLeft(Map.empty[String, String]) { (acc, hook) =>
-      acc ++ hook.run(qbeastActions)
+      acc ++ hook.run(actions)
     }
   }
 
@@ -173,21 +173,24 @@ private[delta] case class DeltaMetadataWriter(
       // Register metrics to use in the Commit Info
       val statsTrackers = createStatsTrackers(txn)
       registerStatsTrackers(statsTrackers)
-      // Execute write
 
-      val (changes, indexFiles, deleteFiles) = writer
+      // Execute write
+      val (tableChanges, indexFiles, deleteFiles) = writer
       val addFiles = indexFiles.map(DeltaQbeastFileUtils.toAddFile(dataChange = true))
       val removeFiles = deleteFiles.map(DeltaQbeastFileUtils.toRemoveFile(dataChange = false))
 
       // Update Qbeast Metadata (replicated set, revision..)
-      var actions = updateMetadata(txn, changes, addFiles, removeFiles)
+      var actions = updateMetadata(txn, tableChanges, addFiles, removeFiles)
       // Set transaction identifier if specified
       for (txnVersion <- options.txnVersion; txnAppId <- options.txnAppId) {
         actions +:= SetTransaction(txnAppId, txnVersion, Some(System.currentTimeMillis()))
       }
 
       // Run pre-commit hooks
-      val tags = runPreCommitHooks(actions)
+      val revision = tableChanges.updatedRevision
+      val dimensionCount = revision.transformations.length
+      val qbeastActions = actions.map(DeltaQbeastFileUtils.fromAction(dimensionCount))
+      val tags = runPreCommitHooks(qbeastActions)
 
       // Commit the information to the DeltaLog
       val op =

delta/src/main/scala/io/qbeast/spark/delta/DeltaQbeastFileUtils.scala

@@ -135,9 +135,9 @@ private[delta] object DeltaQbeastFileUtils {
    * @param action
    *   the action instance
    */
-  def fromAction(action: Action): QbeastFile = {
+  def fromAction(dimensionCount: Int)(action: Action): QbeastFile = {
     action match {
-      case addFile: AddFile => fromAddFile(1)(addFile)
+      case addFile: AddFile => fromAddFile(dimensionCount)(addFile)
       case removeFile: RemoveFile => fromRemoveFile(removeFile)
       case _ => null
     }

delta/src/main/scala/io/qbeast/spark/delta/DeltaQbeastSnapshot.scala

@@ -49,9 +49,9 @@ case class DeltaQbeastSnapshot(tableID: QTableID) extends QbeastSnapshot with De
    */
   override def isInitial: Boolean = snapshot.version == -1
 
-  override val schema: StructType = snapshot.metadata.schema
+  override lazy val schema: StructType = snapshot.metadata.schema
 
-  override val allFilesCount: Long = snapshot.allFiles.count
+  override lazy val allFilesCount: Long = snapshot.allFiles.count
 
   private val metadataMap: Map[String, String] = snapshot.metadata.configuration
 

delta/src/main/scala/io/qbeast/spark/delta/DeltaQbeastStatsUtils.scala

@@ -19,6 +19,7 @@ import com.fasterxml.jackson.core.JsonGenerator
 import com.fasterxml.jackson.core.JsonParseException
 import com.fasterxml.jackson.core.JsonParser
 import com.fasterxml.jackson.databind.module.SimpleModule
+import com.fasterxml.jackson.databind.node.JsonNodeType
 import com.fasterxml.jackson.databind.DeserializationContext
 import com.fasterxml.jackson.databind.JsonDeserializer
 import com.fasterxml.jackson.databind.JsonMappingException
@@ -30,9 +31,12 @@ import io.qbeast.core.model.mapper
 import io.qbeast.core.model.QbeastStats
 
 private[delta] object QbeastStatsUtils {
-  private val module = new SimpleModule()
-  module.addSerializer(classOf[String], new ValueSerializer)
-  module.addDeserializer(classOf[String], new ValueDeserializer)
+
+  val module: SimpleModule = new SimpleModule()
+    .addSerializer(classOf[String], new ValueSerializer)
+    .addDeserializer(classOf[String], new ValueDeserializer)
+    .addDeserializer(classOf[Map[String, String]], new MapDeserializer)
+
   mapper.registerModule(module)
 
   def fromString(jsonString: String): Option[QbeastStats] = {
@@ -55,24 +59,49 @@ private[delta] object QbeastStatsUtils {
 
 }
 
-class ValueSerializer extends JsonSerializer[String] {
+class ValueSerializer extends JsonSerializer[Any] {
 
   override def serialize(
-      value: String,
+      value: Any,
       gen: JsonGenerator,
       serializers: SerializerProvider): Unit = {
-    try {
-      val intValue = value.toInt
-      gen.writeNumber(intValue)
-    } catch {
-      case _: NumberFormatException =>
+    value match {
+      case m: Map[_, _] =>
+        gen.writeStartObject()
+        m.foreach { case (key, v) =>
+          gen.writeFieldName(key.toString)
+          v match {
+            case nestedMap: Map[_, _] =>
+              serialize(nestedMap, gen, serializers)
+            case s: String =>
+              try {
+                val jsonNode = mapper.readTree(s)
+                gen.writeTree(jsonNode)
+              } catch {
+                case _: Exception =>
+                  gen.writeString(s)
+              }
+            case i: Int => gen.writeNumber(i)
+            case l: Long => gen.writeNumber(l)
+            case d: Double => gen.writeNumber(d)
+            case other => gen.writeString(other.toString)
+          }
+        }
+        gen.writeEndObject()
+
+      case s: String =>
         try {
-          val doubleValue = value.toDouble
-          gen.writeNumber(doubleValue)
+          val jsonNode = mapper.readTree(s)
+          gen.writeTree(jsonNode)
         } catch {
-          case _: NumberFormatException =>
-            gen.writeString(value)
+          case _: Exception =>
+            gen.writeString(s)
         }
+
+      case i: Int => gen.writeNumber(i)
+      case l: Long => gen.writeNumber(l)
+      case d: Double => gen.writeNumber(d)
+      case other => gen.writeString(other.toString)
     }
   }
 
@@ -92,3 +121,26 @@ class ValueDeserializer extends JsonDeserializer[String] {
   }
 
 }
+
+class MapDeserializer extends JsonDeserializer[Map[String, String]] {
+
+  override def deserialize(p: JsonParser, ctxt: DeserializationContext): Map[String, String] = {
+    val node = p.getCodec.readTree[JsonNode](p)
+    val mapBuilder = scala.collection.mutable.Map[String, String]()
+
+    if (node.isObject) {
+      node.fields().forEachRemaining { entry =>
+        val key = entry.getKey
+        val valueNode = entry.getValue
+        if (valueNode.getNodeType == JsonNodeType.OBJECT) {
+          mapBuilder(key) = valueNode.toString
+        } else {
+          mapBuilder(key) = valueNode.asText()
+        }
+      }
+    }
+
+    mapBuilder.toMap
+  }
+
+}

delta/src/test/scala/io/qbeast/spark/delta/DeltaQbeastStatsTest.scala

@@ -0,0 +1,102 @@
+/*
+ * Copyright 2021 Qbeast Analytics, S.L.
+ *
+ * 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.qbeast.spark.delta
+
+import com.fasterxml.jackson.databind.JsonNode
+import com.fasterxml.jackson.databind.ObjectMapper
+import io.qbeast.core.model.mapper
+import io.qbeast.core.model.QbeastStats
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+class DeltaQbeastStatsTest extends AnyFlatSpec with Matchers {
+
+  mapper.registerModule(QbeastStatsUtils.module)
+
+  def areJsonEqual(json1: String, json2: String): Boolean = {
+    val basicMapper = new ObjectMapper()
+
+    try {
+      val node1: JsonNode = basicMapper.readTree(json1)
+      val node2: JsonNode = basicMapper.readTree(json2)
+
+      node1.equals(node2)
+    } catch {
+      case e: Exception =>
+        println(s"Error parsing JSON: ${e.getMessage}")
+        false
+    }
+  }
+
+  "ValueSerializer" should "serialize a numeric string to a number" in {
+    val json = mapper.writeValueAsString("123") // This uses ValueSerializer
+    json shouldEqual "123" // It should output a number in JSON
+  }
+
+  it should "serialize a non-numeric string as is" in {
+    val json = mapper.writeValueAsString("hello") // This uses ValueSerializer
+    json shouldEqual "\"hello\""
+  }
+
+  "ValueDeserializer" should "deserialize a number string to a string" in {
+    val value = mapper.readValue("123", classOf[String]) // This uses ValueDeserializer
+    value shouldEqual "123"
+  }
+
+  it should "deserialize a textual value as is" in {
+    val value = mapper.readValue("\"hello\"", classOf[String]) // This uses ValueDeserializer
+    value shouldEqual "hello"
+  }
+
+  "MapDeserializer" should "deserialize a JSON object to a Map[String, String]" in {
+    val json = """{"key1": "value1", "key2": {"innerKey": "innerValue"}}"""
+    val result = mapper.readValue(json, classOf[Map[String, String]]) // This uses MapDeserializer
+
+    result should contain("key1" -> "value1")
+    result should contain("key2" -> """{"innerKey":"innerValue"}""")
+  }
+
+  "QbeastStatsUtils" should "serialize and deserialize correctly" in {
+    val jsonString =
+      """{"numRecords":52041,"minValues":{"key1": "value1", "key2": {"innerKey": "innerValue"}},
+        |"maxValues":{"key3": "value3", "key4": "value4"},"nullCount":{"key5": 0, "key6": 2}}""".stripMargin
+
+    // Create the expected QbeastStats object
+    val expectedStats = QbeastStats(
+      numRecords = 52041,
+      minValues = Map("key2" -> """{"innerKey":"innerValue"}""", "key1" -> "value1"),
+      maxValues = Map("key3" -> "value3", "key4" -> "value4"),
+      nullCount = Map("key5" -> "0", "key6" -> "2"))
+
+    // Deserialize the JSON string
+    val deserializedStats = QbeastStatsUtils.fromString(jsonString)
+
+    // Verify that deserialization was successful and matches expected values
+    deserializedStats shouldBe defined // Ensure deserialization was successful
+
+    deserializedStats.foreach { ds =>
+      ds.numRecords shouldEqual expectedStats.numRecords
+      ds.minValues should contain theSameElementsAs expectedStats.minValues
+      ds.maxValues should contain theSameElementsAs expectedStats.maxValues
+      ds.nullCount should contain theSameElementsAs expectedStats.nullCount
+    }
+
+    // Serialize back to JSON string and verify it matches the original
+    val serializedJsonString = QbeastStatsUtils.toString(deserializedStats.get)
+    areJsonEqual(serializedJsonString, jsonString) shouldBe true
+  }
+
+}

src/main/scala/io/qbeast/sources/QbeastBaseRelation.scala

@@ -58,15 +58,14 @@ object QbeastBaseRelation {
     val spark = SparkSession.active
     val tableID = table.tableID
     val snapshot = QbeastContext.metadataManager.loadSnapshot(tableID)
-    val schema = QbeastContext.metadataManager.loadCurrentSchema(tableID)
     if (snapshot.isInitial) {
       // If the Table is initial, read empty relation
       // This could happen if we CREATE/REPLACE TABLE without inserting data
       // In this case, we use the options variable
       new HadoopFsRelation(
         EmptyFileIndex,
         partitionSchema = StructType(Seq.empty[StructField]),
-        dataSchema = schema,
+        dataSchema = snapshot.schema,
         bucketSpec = None,
         new ParquetFileFormat(),
         options)(spark) with InsertableRelation {
@@ -87,7 +86,7 @@ object QbeastBaseRelation {
       new HadoopFsRelation(
         fileIndex,
         partitionSchema = StructType(Seq.empty[StructField]),
-        dataSchema = schema,
+        dataSchema = snapshot.schema,
         bucketSpec = bucketSpec,
         file,
         parameters)(spark) with InsertableRelation {

src/test/scala/io/qbeast/spark/delta/QbeastDeltaIntegrationTest.scala

@@ -15,6 +15,8 @@
  */
 package io.qbeast.spark.delta
 
+import com.fasterxml.jackson.databind.JsonNode
+import com.fasterxml.jackson.databind.ObjectMapper
 import io.delta.tables._
 import io.qbeast.QbeastIntegrationTestSpec
 import org.apache.spark.sql.delta.DeltaLog
@@ -31,6 +33,21 @@ class QbeastDeltaIntegrationTest extends QbeastIntegrationTestSpec {
     Seq(("A", 1), ("B", 2), ("C", 3)).toDF("a", "b")
   }
 
+  def areJsonEqual(json1: String, json2: String): Boolean = {
+    val basicMapper = new ObjectMapper()
+
+    try {
+      val node1: JsonNode = basicMapper.readTree(json1)
+      val node2: JsonNode = basicMapper.readTree(json2)
+
+      node1.equals(node2)
+    } catch {
+      case e: Exception =>
+        println(s"Error parsing JSON: ${e.getMessage}")
+        false
+    }
+  }
+
   "Qbeast" should "output correctly Operation Metrics in Delta History" in
     withQbeastContextSparkAndTmpDir((spark, tmpDir) => {
 
@@ -63,10 +80,13 @@ class QbeastDeltaIntegrationTest extends QbeastIntegrationTestSpec {
       val stats =
         DeltaLog.forTable(spark, tmpDir).unsafeVolatileSnapshot.allFiles.collect().map(_.stats)
       stats.length shouldBe >(0)
-      stats.head shouldBe "{\"numRecords\":3,\"minValues\":{\"a\":\"A\",\"b\":1}," +
-        "\"maxValues\":{\"a\":\"C\",\"b\":3}," +
-        "\"nullCount\":{\"a\":0,\"b\":0}}"
 
+      val expectedStats =
+        """{"numRecords":3,"minValues":{"a":"A","b":1},
+          |"maxValues":{"a":"C","b":3},
+          |"nullCount":{"a":0,"b":0}}""".stripMargin
+
+      areJsonEqual(stats.head, expectedStats) shouldBe true
     })
 
   it should "not write stats when specified" in withExtendedSparkAndTmpDir(