1.1

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -21,3 +21,5 @@ gradle-app.setting
 # JDT-specific (Eclipse Java Development Tools)
 .classpath
 
+.direnv
+bin

build.gradle.kts

@@ -1,7 +1,7 @@
 import net.minecrell.pluginyml.bukkit.BukkitPluginDescription
 
 group = "net.hareworks"
-version = "1.0"
+version = "1.1"
 
 val exposedVersion = "0.54.0"
 
@@ -9,7 +9,7 @@ plugins {
     kotlin("jvm") version "2.0.20"
     kotlin("plugin.serialization") version "2.0.20"
     id("net.minecrell.plugin-yml.bukkit") version "0.6.0"
-    id("com.github.johnrengelman.shadow") version "8.1.1"
+    id("com.gradleup.shadow") version "9.2.2"
 }
 repositories {
     mavenCentral()
@@ -17,23 +17,28 @@ repositories {
     maven("https://repo.codemc.io/repository/maven-public/")
 }
 dependencies {
-    compileOnly("io.papermc.paper:paper-api:1.21.3-R0.1-SNAPSHOT")
+    compileOnly("io.papermc.paper:paper-api:1.21.10-R0.1-SNAPSHOT")
     implementation("net.kyori:adventure-api:4.17.0")
     implementation("net.kyori:adventure-text-minimessage:4.17.0")
-    // implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.7.1")
+    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.7.1")
     implementation("org.postgresql:postgresql:42.7.1")
     implementation("org.jetbrains.exposed:exposed-core:$exposedVersion")
     implementation("org.jetbrains.exposed:exposed-dao:$exposedVersion")
     implementation("org.jetbrains.exposed:exposed-jdbc:$exposedVersion")
     implementation("org.jetbrains.kotlinx:kotlinx-datetime:0.6.1")
     implementation("org.jetbrains.exposed:exposed-kotlin-datetime:$exposedVersion")
-    compileOnly("de.tr7zw:item-nbt-api-plugin:2.14.0")
+    implementation("de.tr7zw:item-nbt-api:2.15.3")
     implementation("com.michael-bull.kotlin-result:kotlin-result:2.0.0")
 }
 tasks {
     shadowJar {
         archiveBaseName.set("SimplyMCDB")
         archiveClassifier.set("")
+        relocate("de.tr7zw.changeme.nbtapi", "net.hareworks.simplymcdb.libs.nbtapi")
+    }
+
+    build {
+        dependsOn(shadowJar)
     }
 }
 
@@ -42,10 +47,9 @@ bukkit {
     name = "Simply-Minecraft-DB"
     description = "It provides a simple way to manage player data through a database."
     version = getVersion().toString()
-		apiVersion = "1.21.3"
+		apiVersion = "1.21.10"
     authors =
             listOf("Hare-K02")
-    depend = listOf("NBTAPI")
     permissions {
         register("simplydb.*") {
             children = listOf("simplydb.command", "simplydb.admin")

flake.lock

@@ -0,0 +1,61 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1764020296,
+        "narHash": "sha256-6zddwDs2n+n01l+1TG6PlyokDdXzu/oBmEejcH5L5+A=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "a320ce8e6e2cc6b4397eef214d202a50a4583829",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-25.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,47 @@
+{
+  description = "Minecraft dev environment with JDK 21 and Gradle";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+      ...
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+        };
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          packages = with pkgs; [
+            jdk21
+            gradle
+            kotlin
+            git
+            unzip
+          ];
+
+          # 必要に応じて環境変数を設定
+          shellHook = ''
+            export JAVA_HOME=${pkgs.jdk21}/lib/openjdk
+            export PATH="$JAVA_HOME/bin:$PATH"
+
+            export GRADLE_USER_HOME="$PWD/.gradle"
+
+            echo "Loaded Minecraft dev env (JDK 21 + Gradle)"
+            java -version || true
+            gradle --version || true
+          '';
+        };
+      }
+    );
+}

gradle/gradle-daemon-jvm.properties

@@ -0,0 +1,2 @@
+#This file is generated by updateDaemonJvm
+toolchainVersion=21

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,7 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.10.1-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14-bin.zip
 networkTimeout=10000
+validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists

gradlew

@@ -15,6 +15,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
+# SPDX-License-Identifier: Apache-2.0
+#
 
 ##############################################################################
 #
@@ -55,7 +57,7 @@
 #       Darwin, MinGW, and NonStop.
 #
 #   (3) This script is generated from the Groovy template
-#       https://github.com/gradle/gradle/blob/HEAD/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       https://github.com/gradle/gradle/blob/HEAD/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
 #       within the Gradle project.
 #
 #       You can find Gradle at https://github.com/gradle/gradle/.
@@ -83,10 +85,9 @@ done
 # This is normally unused
 # shellcheck disable=SC2034
 APP_BASE_NAME=${0##*/}
-APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
-
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s
-# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+' "$PWD" ) || exit
-DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
 
 # Use the maximum available, or set MAX_FD != -1 to use that value.
 MAX_FD=maximum
@@ -133,10 +134,13 @@ location of your Java installation."
     fi
 else
     JAVACMD=java
-    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
 
 Please set the JAVA_HOME variable in your environment to match the
 location of your Java installation."
+    fi
 fi
 
 # Increase the maximum file descriptors if we can.
@@ -144,7 +148,7 @@ if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
     case $MAX_FD in #(
       max*)
         # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
-        # shellcheck disable=SC3045
+        # shellcheck disable=SC2039,SC3045
         MAX_FD=$( ulimit -H -n ) ||
             warn "Could not query maximum file descriptor limit"
     esac
@@ -152,7 +156,7 @@ if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
       '' | soft) :;; #(
       *)
         # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
-        # shellcheck disable=SC3045
+        # shellcheck disable=SC2039,SC3045
         ulimit -n "$MAX_FD" ||
             warn "Could not set maximum file descriptor limit to $MAX_FD"
     esac
@@ -197,11 +201,15 @@ if "$cygwin" || "$msys" ; then
     done
 fi
 
-# Collect all arguments for the java command;
+
-#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
-#     shell script including quotes and variable substitutions, so put them in
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
-#     double quotes to make sure that they get re-expanded; and
+
-#   * put everything else in single quotes, so that it's not re-expanded.
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
 
 set -- \
         "-Dorg.gradle.appname=$APP_BASE_NAME" \

gradlew.bat

@@ -13,6 +13,8 @@
 @rem See the License for the specific language governing permissions and
 @rem limitations under the License.
 @rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
 
 @if "%DEBUG%"=="" @echo off
 @rem ##########################################################################
@@ -43,11 +45,11 @@ set JAVA_EXE=java.exe
 %JAVA_EXE% -version >NUL 2>&1
 if %ERRORLEVEL% equ 0 goto execute
 
-echo.
+echo. 1>&2
-echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
-echo.
+echo. 1>&2
-echo Please set the JAVA_HOME variable in your environment to match the
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
-echo location of your Java installation.
+echo location of your Java installation. 1>&2
 
 goto fail
 
@@ -57,11 +59,11 @@ set JAVA_EXE=%JAVA_HOME%/bin/java.exe
 
 if exist "%JAVA_EXE%" goto execute
 
-echo.
+echo. 1>&2
-echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
-echo.
+echo. 1>&2
-echo Please set the JAVA_HOME variable in your environment to match the
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
-echo location of your Java installation.
+echo location of your Java installation. 1>&2
 
 goto fail
 

src/main/kotlin/net/hareworks/simplymcdb/App.kt

@@ -18,10 +18,12 @@ public class App : JavaPlugin() {
       field = value
       Config.config.set("enabled", !value.equals(State.DISABLED))
     }
+
   companion object {
     lateinit var instance: App
       private set
   }
+
   lateinit var command: KommandLib
     private set
 
@@ -34,6 +36,7 @@ public class App : JavaPlugin() {
 
     if (Config.check()) enable()
   }
+
   override fun onDisable() {
     enabled = State.DISABLED
     Database.disconnect()

src/main/kotlin/net/hareworks/simplymcdb/Command.kt

@@ -72,6 +72,91 @@ public val smcdb =
                                           sender.sendMessage("database reset.")
                                         },
                                 ),
+                        Route("migrate") { sender, _ ->
+                          if (sender !is Player) {
+                            sender.sendMM("<red>[SMCDB] This command can only be run by players.")
+                            return@Route
+                          }
+                          when (App.instance.enabled) {
+                            State.DISABLED -> {
+                              sender.sendMM("<red>[SMCDB] simplymcdb is disabled.")
+                              return@Route
+                            }
+                            State.DISCONNECTED -> {
+                              sender.sendMM("<yellow>[SMCDB] Database disconnected. Try again later.")
+                              return@Route
+                            }
+                            else -> {}
+                          }
+                          if (!isRegistered(sender.uniqueId)) {
+                            sender.sendMM("<red>[SMCDB] You are not registered in the database.")
+                            return@Route
+                          }
+                          try {
+                            sender.sendMM("<gray>[SMCDB] Applying legacy data...")
+                            fetch(sender)
+                            update(sender)
+                            sender.sendMM("<green>[SMCDB] Migration complete. Data updated to the latest format.")
+                          } catch (e: Exception) {
+                            App.instance.logger.warning("Failed to migrate data for ${sender.uniqueId}: ${e.message}")
+                            sender.sendMM("<red>[SMCDB] Migration failed. Check server logs.")
+                          }
+                        }.addArgs(
+                                Route("all") { sender, _ ->
+                                  if (sender !is Player) {
+                                    sender.sendMM("<red>[SMCDB] This command can only be run by players.")
+                                    return@Route
+                                  }
+                                  when (App.instance.enabled) {
+                                    State.DISABLED -> {
+                                      sender.sendMM("<red>[SMCDB] simplymcdb is disabled.")
+                                      return@Route
+                                    }
+                                    State.DISCONNECTED -> {
+                                      sender.sendMM(
+                                              "<yellow>[SMCDB] Database disconnected. Try again later."
+                                      )
+                                      return@Route
+                                    }
+                                    else -> {}
+                                  }
+                                  val targets = findPlayersNeedingMigration()
+                                  if (targets.isEmpty()) {
+                                    sender.sendMM("<gray>[SMCDB] No legacy data found.")
+                                    return@Route
+                                  }
+                                  sender.sendMM(
+                                          "<gray>[SMCDB] Migrating ${targets.size} legacy profiles... Please wait."
+                                  )
+                                  val backup = PlayerSerializer.serialize(sender)
+                                  var migrated = 0
+                                  try {
+                                    targets.forEach { entry ->
+                                      try {
+                                        PlayerSerializer.deserialize(sender, entry.serialized)
+                                        val updatedSnapshot = PlayerSerializer.serialize(sender)
+                                        overwritePlayerData(entry.uuid, updatedSnapshot)
+                                        migrated++
+                                      } catch (ex: Exception) {
+                                        App.instance.logger.warning(
+                                                "Failed to migrate data for ${entry.uuid}: ${ex.message}"
+                                        )
+                                      }
+                                    }
+                                  } finally {
+                                    try {
+                                      PlayerSerializer.deserialize(sender, backup)
+                                    } catch (restoreEx: Exception) {
+                                      App.instance.logger.warning(
+                                              "Failed to restore migration executor state: ${restoreEx.message}"
+                                      )
+                                    }
+                                  }
+                                  sender.sendMM(
+                                          "<green>[SMCDB] Migration finished ($migrated/${targets.size}). Check logs for failures."
+                                  )
+                                }
+                        ),
                         Route("check") { sender, _ ->
                           sender.sendMM(
                                   "${when (App.instance.enabled) {

src/main/kotlin/net/hareworks/simplymcdb/Event.kt

@@ -46,18 +46,15 @@ public object EventListener : Listener {
     |    not     | confirm  register |
     +------------+------------------*/
     if (isRegistered(event.player.uniqueId)) fetch(event.player)
-    else if (event.player.hasPlayedBefore()) {
+    else if (event.player.hasPlayedBefore()) register(event.player)
-      register(event.player)
+    else event.player.sendMessage(
-    } else {
+      MiniMessage.miniMessage()
-      event.player.sendMessage(
+        .deserialize(
-              MiniMessage.miniMessage()
+          "<gray>[SMCDB] Welcome, ${event.player.name}.<newline>" +
-                      .deserialize(
+          "SMCDB is active but you have already played before.<newline>" +
-                              "<gray>[SMCDB] Welcome, ${event.player.name}.<newline>" +
+          "Run <green>/smcdb register<gray> to register yourself."
-                                      "SMCDB is active but you have already played before.<newline>" +
-                                      "Run <green>/smcdb register<gray> to register yourself."
-                      )
       )
-    }
+    )
   }
 
   @EventHandler

src/main/kotlin/net/hareworks/simplymcdb/PlayerSerializer.kt

@@ -1,68 +1,179 @@
 package net.hareworks.simplymcdb
 
-import de.tr7zw.nbtapi.NBT
+import de.tr7zw.changeme.nbtapi.NBT
+import java.util.Base64
 import java.util.function.Function
+import io.papermc.paper.registry.RegistryAccess
+import io.papermc.paper.registry.RegistryKey
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.SerializationException
+import kotlinx.serialization.json.Json
+import org.bukkit.NamespacedKey
+import org.bukkit.Registry
+import org.bukkit.attribute.Attribute
 import org.bukkit.entity.Player as BukkitPlayer
+import org.bukkit.inventory.ItemStack
+import org.bukkit.potion.PotionEffect
+import org.bukkit.potion.PotionEffectType
 
-data class PlayerData(
+const val PLAYER_DATA_CURRENT_VERSION = 1
-        val health: Float,
+
-        val hunger: Int,
+@Serializable
-        val exp: Float,
+data class PlayerSnapshot(
-        val effects: String,
+        val version: Int = PLAYER_DATA_CURRENT_VERSION,
-        val inv: String,
+        val health: Double,
-        val enderchest: String
+        val foodLevel: Int,
+        val xpProgress: Float,
+        val selectedItemSlot: Int,
+        val potionEffects: List<PotionEffectSnapshot>,
+        val inventory: List<ItemStackSnapshot?>,
+        val enderChest: List<ItemStackSnapshot?>
 )
 
+@Serializable
+data class PotionEffectSnapshot(
+        val type: String,
+        val amplifier: Int,
+        val duration: Int,
+        val ambient: Boolean,
+        val particles: Boolean,
+        val icon: Boolean
+)
+
+@Serializable data class ItemStackSnapshot(val payload: String)
+
+private val json =
+        Json {
+          encodeDefaults = true
+          ignoreUnknownKeys = true
+        }
+private val mobEffectRegistry: Registry<PotionEffectType>?
+  get() = RegistryAccess.registryAccess().getRegistry(RegistryKey.MOB_EFFECT)
+
 object PlayerSerializer {
   fun serialize(player: BukkitPlayer): String {
-    val result =
+    val snapshot =
-            NBT.get(
+            PlayerSnapshot(
-                    player,
+                    health = player.health,
-                    Function { nbt ->
+                    foodLevel = player.foodLevel,
-                      var output = NBT.createNBTObject()
+                    xpProgress = player.exp,
-
+                    selectedItemSlot = player.inventory.heldItemSlot,
-                      output.setFloat("Health", player.health.toFloat())
+                    potionEffects = player.activePotionEffects.map(::serializePotionEffect),
-                      output.setInteger("foodLevel", player.foodLevel)
+                    inventory = player.inventory.contents.map { it?.let(::serializeItemStack) },
-                      output.setFloat("XpP", player.exp)
+                    enderChest = player.enderChest.contents.map { it?.let(::serializeItemStack) }
-                      output.setInteger("SelectedItemSlot", player.inventory.heldItemSlot)
-                      var active_effects = output.getCompoundList("active_effects")
-                      nbt.getCompoundList("active_effects").forEach {
-                        active_effects.addCompound(it)
-                      }
-                      var inventory = output.getCompoundList("Inventory")
-                      nbt.getCompoundList("Inventory").forEach { inventory.addCompound(it) }
-                      var enderchest = output.getCompoundList("EnderItems")
-                      nbt.getCompoundList("EnderItems").forEach { enderchest.addCompound(it) }
-
-                      output.toString()
-                    }
             )
-    return result
+    return json.encodeToString(PlayerSnapshot.serializer(), snapshot)
   }
 
   fun deserialize(player: BukkitPlayer, data: String) {
-    NBT.modify(
+    val snapshot =
-            player,
+            try {
-            Function { nbt ->
+              json.decodeFromString(PlayerSnapshot.serializer(), data)
-              val input = NBT.parseNBT(data)
+            } catch (ex: SerializationException) {
-
+              if (LegacySerializer.deserialize(player, data)) return else throw ex
-              App.instance.logger.info("Deserializing player data: $data")
+            } catch (ex: IllegalArgumentException) {
-              App.instance.logger.info("deserialized: ${input.toString()}")
+              if (LegacySerializer.deserialize(player, data)) return else throw ex
-
-              nbt.setFloat("Health", input.getFloat("Health"))
-              nbt.setInteger("foodLevel", input.getInteger("foodLevel"))
-              nbt.setFloat("XpP", input.getFloat("XpP"))
-              nbt.setInteger("SelectedItemSlot", input.getInteger("SelectedItemSlot"))
-              val active_effects = nbt.getCompoundList("active_effects")
-              active_effects.clear()
-              input.getCompoundList("active_effects").forEach { active_effects.addCompound(it) }
-              val inventory = nbt.getCompoundList("Inventory")
-              inventory.clear()
-              input.getCompoundList("Inventory").forEach { inventory.addCompound(it) }
-              val enderchest = nbt.getCompoundList("EnderItems")
-              enderchest.clear()
-              input.getCompoundList("EnderItems").forEach { enderchest.addCompound(it) }
             }
-    )
+    applySnapshot(player, migrateIfNeeded(snapshot))
+  }
+
+  private fun migrateIfNeeded(snapshot: PlayerSnapshot): PlayerSnapshot {
+    var current = snapshot
+    var version = snapshot.version
+    while (version < PLAYER_DATA_CURRENT_VERSION) {
+      current = migrateOnce(version, current)
+      version++
+    }
+    return current
+  }
+
+  private fun migrateOnce(fromVersion: Int, snapshot: PlayerSnapshot): PlayerSnapshot {
+    return when (fromVersion) {
+      1 -> snapshot
+      else -> snapshot
+    }
+  }
+
+  private fun applySnapshot(player: BukkitPlayer, snapshot: PlayerSnapshot) {
+    val maxHealth = player.getAttribute(Attribute.MAX_HEALTH)?.value ?: player.health
+    player.health = snapshot.health.coerceIn(0.0, maxHealth)
+    player.foodLevel = snapshot.foodLevel.coerceIn(0, 20)
+    player.exp = snapshot.xpProgress.coerceIn(0f, 1f)
+    player.inventory.heldItemSlot =
+            snapshot.selectedItemSlot.coerceIn(0, player.inventory.contents.size - 1)
+
+    player.activePotionEffects.forEach { player.removePotionEffect(it.type) }
+    snapshot.potionEffects.forEach { eff ->
+      val typeKey = NamespacedKey.fromString(eff.type)
+      val type = typeKey?.let { key -> mobEffectRegistry?.get(key) }
+      if (type == null) {
+        App.instance.logger.warning("Unknown potion effect key during restore: ${eff.type}")
+        return@forEach
+      }
+      val potion = PotionEffect(type, eff.duration, eff.amplifier, eff.ambient, eff.particles, eff.icon)
+      player.addPotionEffect(potion)
+    }
+
+    player.inventory.clear()
+    snapshot.inventory.forEachIndexed { index, item ->
+      player.inventory.setItem(index, item?.let(::deserializeItemStack))
+    }
+
+    player.enderChest.clear()
+    snapshot.enderChest.forEachIndexed { index, item ->
+      player.enderChest.setItem(index, item?.let(::deserializeItemStack))
+    }
+  }
+}
+
+private fun serializePotionEffect(effect: PotionEffect): PotionEffectSnapshot {
+  val typeKey = effect.type.key().toString()
+  return PotionEffectSnapshot(
+          type = typeKey,
+          amplifier = effect.amplifier,
+          duration = effect.duration,
+          ambient = effect.isAmbient,
+          particles = effect.hasParticles(),
+          icon = effect.hasIcon()
+  )
+}
+
+private fun serializeItemStack(item: ItemStack): ItemStackSnapshot {
+  val bytes = item.ensureServerConversions().serializeAsBytes()
+  return ItemStackSnapshot(Base64.getEncoder().encodeToString(bytes))
+}
+
+private fun deserializeItemStack(snapshot: ItemStackSnapshot): ItemStack {
+  val data = Base64.getDecoder().decode(snapshot.payload)
+  return ItemStack.deserializeBytes(data)
+}
+
+private object LegacySerializer {
+  fun deserialize(player: BukkitPlayer, data: String): Boolean {
+    return try {
+      NBT.modify(
+              player,
+              Function { nbt ->
+                val input = NBT.parseNBT(data)
+                nbt.setFloat("Health", input.getFloat("Health"))
+                nbt.setInteger("foodLevel", input.getInteger("foodLevel"))
+                nbt.setFloat("XpP", input.getFloat("XpP"))
+                nbt.setInteger("SelectedItemSlot", input.getInteger("SelectedItemSlot"))
+                val activeEffects = nbt.getCompoundList("active_effects")
+                activeEffects.clear()
+                input.getCompoundList("active_effects").forEach { activeEffects.addCompound(it) }
+                val inventory = nbt.getCompoundList("Inventory")
+                inventory.clear()
+                input.getCompoundList("Inventory").forEach { inventory.addCompound(it) }
+                val enderchest = nbt.getCompoundList("EnderItems")
+                enderchest.clear()
+                input.getCompoundList("EnderItems").forEach { enderchest.addCompound(it) }
+              }
+      )
+      App.instance.logger.info("Legacy player data applied; will be migrated on next save.")
+      true
+    } catch (_: Exception) {
+      false
+    }
   }
 }

src/main/kotlin/net/hareworks/simplymcdb/Players.kt

@@ -17,6 +17,7 @@ public object Players : Table() {
   val lastIp = varchar("last_ip", 15)
 
   val data = text("data").default("")
+  val dataVersion = integer("data_version").default(0)
 
   override val primaryKey = PrimaryKey(uuid)
 }
@@ -39,6 +40,7 @@ public fun register(player: BukkitPlayer) {
       it[firstLogin] = System.currentTimeMillis()
       it[lastOnline] = System.currentTimeMillis()
       it[lastIp] = player.address?.address?.hostAddress ?: "unknown"
+      it[dataVersion] = 0
     }
   }
 }
@@ -52,6 +54,7 @@ public fun update(player: BukkitPlayer) {
 
       // player.sendMessage(dat)
       it[data] = dat
+      it[dataVersion] = PLAYER_DATA_CURRENT_VERSION
     }
   }
 }
@@ -68,3 +71,25 @@ public fun fetch(player: BukkitPlayer) {
   // player.sendMessage(dat)
   PlayerSerializer.deserialize(player, dat)
 }
+
+data class PlayerDataEntry(val uuid: UUID, val serialized: String, val version: Int)
+
+public fun findPlayersNeedingMigration(): List<PlayerDataEntry> {
+  return transaction(Database.instance) {
+    Players
+            .selectAll()
+            .where { (Players.dataVersion less PLAYER_DATA_CURRENT_VERSION) and (Players.data neq "") }
+            .map {
+              PlayerDataEntry(UUID.fromString(it[Players.uuid]), it[Players.data], it[Players.dataVersion])
+            }
+  }
+}
+
+public fun overwritePlayerData(uuid: UUID, data: String, version: Int = PLAYER_DATA_CURRENT_VERSION) {
+  transaction(Database.instance) {
+    Players.update({ Players.uuid eq uuid.toString() }) {
+      it[Players.data] = data
+      it[Players.dataVersion] = version
+    }
+  }
+}

src/main/kotlin/net/hareworks/simplymcdb/database/Database.kt

@@ -51,6 +51,7 @@ public object Database {
     }
     if (instance == null) return
     App.instance.logger.info("Database connected: $host:$port/$database")
+    transaction(instance) { SchemaUtils.createMissingTablesAndColumns(Players) }
   }
   public fun disconnect() {
     instance?.let {