Fixes #16

Detailed research revealed that we're incorrectly inferring field names
if they don't confirm to javaBean specification. It turns out that we're
inferring field name from getter which is not always correct.

So in this commit we're adding new wrapper KStructField, which contains
information not only on field name, but also information on getter name
which gives us abiity to filter data not by inferred field name, but
by getter name which is much more safe - there is no way kotlin will
allow the scapitalized and non capitalized properties to co-exist in
same class, like `Country` and `country`, so usage of getter looks more
correct way to handle this situation.

Signed-off-by: Pasha Finkelshteyn <asm0dey@jetbrains.com>

core/src/main/scala/org/apache/spark/sql/KotlinReflection.scala

@@ -653,10 +653,11 @@ object KotlinReflection extends KotlinReflection {
             val cls = dataType.cls
             val properties = getJavaBeanReadableProperties(cls)
             val fields = properties.map { prop =>
-              val fieldName = prop.getName
-              val maybeField = dataType.dt.fields.find(it => it.name == fieldName)
+
+              val maybeField = dataType.dt.fields.map(_.asInstanceOf[KStructField]).find(it => it.getterName == prop.getReadMethod.getName)
               if (maybeField.isEmpty)
-                throw new IllegalArgumentException(s"Field $fieldName is not found among available fields, which are: ${dataType.dt.fields.map(_.name).mkString(", ")}")
+                throw new IllegalArgumentException(s"Field ${prop.getName} is not found among available fields, which are: ${dataType.dt.fields.map(_.name).mkString(", ")}")
+              val fieldName = maybeField.get.name
               val propClass = maybeField.map(it => it.dataType.asInstanceOf[DataTypeWithClass].cls).get
               val propDt = maybeField.map(it => it.dataType.asInstanceOf[DataTypeWithClass]).get
 

core/src/main/scala/org/apache/spark/sql/KotlinWrappers.scala

@@ -178,6 +178,36 @@ case class KSimpleTypeWrapper(dt: DataType, cls: Class[_], nullable: Boolean) ex
   override private[spark] def asNullable = dt.asNullable
 }
 
+class KStructField(val getterName: String, val delegate: StructField) extends StructField {
+  override private[sql] def buildFormattedString(prefix: String, stringConcat: StringUtils.StringConcat, maxDepth: Int): Unit = delegate.buildFormattedString(prefix, stringConcat, maxDepth)
+
+  override def toString(): String = delegate.toString()
+
+  override private[sql] def jsonValue = delegate.jsonValue
+
+  override def withComment(comment: String): StructField = delegate.withComment(comment)
+
+  override def getComment(): Option[String] = delegate.getComment()
+
+  override def toDDL: String = delegate.toDDL
+
+  override def productElement(n: Int): Any = delegate.productElement(n)
+
+  override def productArity: Int = delegate.productArity
+
+  override def productIterator: Iterator[Any] = delegate.productIterator
+
+  override def productPrefix: String = delegate.productPrefix
+
+  override val dataType: DataType = delegate.dataType
+
+  override def canEqual(that: Any): Boolean = delegate.canEqual(that)
+
+  override val metadata: Metadata = delegate.metadata
+  override val name: String = delegate.name
+  override val nullable: Boolean = delegate.nullable
+}
+
 object helpme {
 
   def listToSeq(i: java.util.List[_]): Seq[_] = Seq(i.toArray: _*)

kotlin-spark-api/src/main/kotlin/org/jetbrains/spark/api/ApiV1.kt

@@ -21,14 +21,14 @@
 
 package org.jetbrains.spark.api
 
-import org.apache.spark.SparkContext
 import org.apache.spark.api.java.function.*
 import org.apache.spark.sql.*
 import org.apache.spark.sql.Encoders.*
 import org.apache.spark.sql.catalyst.encoders.ExpressionEncoder
 import org.apache.spark.sql.types.*
 import org.jetbrains.spark.extensions.KSparkExtensions
 import scala.reflect.ClassTag
+import java.beans.PropertyDescriptor
 import java.math.BigDecimal
 import java.sql.Date
 import java.sql.Timestamp
@@ -281,20 +281,20 @@ fun schema(type: KType, map: Map<String, KType> = mapOf()): DataType {
                     mapValueParam.isMarkedNullable
             )
         }
-        else -> KDataTypeWrapper(
-                StructType(
-                        klass
-                                .declaredMemberProperties
-                                .filter { it.findAnnotation<Transient>() == null }
-                                .map {
-                                    val projectedType = types[it.returnType.toString()] ?: it.returnType
-                                    StructField(it.name, schema(projectedType, types), projectedType.isMarkedNullable, Metadata.empty())
-                                }
-                                .toTypedArray()
-                ),
-                klass.java,
-                true
-        )
+        else -> {
+            val structType = StructType(
+                    klass
+                            .declaredMemberProperties
+                            .filter { it.findAnnotation<Transient>() == null }
+                            .map {
+                                val projectedType = types[it.returnType.toString()] ?: it.returnType
+                                val propertyDescriptor = PropertyDescriptor(it.name, klass.java, "is" + it.name.capitalize(), null)
+                                KStructField(propertyDescriptor.readMethod.name, StructField(it.name, schema(projectedType, types), projectedType.isMarkedNullable, Metadata.empty()))
+                            }
+                            .toTypedArray()
+            )
+            KDataTypeWrapper(structType, klass.java, true)
+        }
     }
 }