docs: Add missing KDocs for exposed-dao EntityClass API

exposed-dao/src/main/kotlin/org/jetbrains/exposed/dao/EntityBatchUpdate.kt

@@ -6,10 +6,24 @@ import org.jetbrains.exposed.sql.Transaction
 import org.jetbrains.exposed.sql.statements.BatchUpdateStatement
 import java.util.*
 
+/**
+ * Class responsible for performing a batch update operation on multiple instances of an [Entity] class.
+ *
+ * @param klass The [EntityClass] associated with the entities to batch update.
+ */
 class EntityBatchUpdate(private val klass: EntityClass<*, Entity<*>>) {
 
     private val data = ArrayList<Pair<EntityID<*>, SortedMap<Column<*>, Any?>>>()
 
+    /**
+     * Adds the specified [entity] to the list of entities to batch update.
+     *
+     * The column-value mapping for this entity will initially be empty.
+     * Columns to update should be assigned by using the `set()` operator on this [EntityBatchUpdate] instance.
+     *
+     * @throws IllegalStateException If the entity being added cannot be associated with the [EntityClass]
+     * provided on instantiation of this [EntityBatchUpdate].
+     */
     fun addBatch(entity: Entity<*>) {
         if (entity.klass != klass) error("Entity class${entity.klass} differs from expected entity class $klass")
         data.add(entity.id to TreeMap())
@@ -25,6 +39,10 @@ class EntityBatchUpdate(private val klass: EntityClass<*, Entity<*>>) {
         values[column] = value
     }
 
+    /**
+     * Executes the batch update SQL statement for each added entity in the provided [transaction]
+     * and returns the number of updated rows.
+     */
     fun execute(transaction: Transaction): Int {
         val updateSets = data.filterNot { it.second.isEmpty() }.groupBy { it.second.keys }
         return updateSets.values.fold(0) { acc, set ->