Add DatabaseConfiguration.downgrade

sqliter-driver/src/nativeCommonMain/kotlin/co/touchlab/sqliter/DatabaseConfiguration.kt

@@ -35,6 +35,9 @@ data class DatabaseConfiguration(
     val version: Int,
     val create: (DatabaseConnection) -> Unit,
     val upgrade: (DatabaseConnection, Int, Int) -> Unit = { _, _, _ -> },
+    val downgrade: (DatabaseConnection, Int, Int) -> Unit = { _, initialVersion, version ->
+        error("Database version $initialVersion newer than config version $version")
+    },
     val inMemory: Boolean = false,
     val journalMode: JournalMode = JournalMode.WAL,
     val extendedConfig:Extended = Extended(),

sqliter-driver/src/nativeCommonMain/kotlin/co/touchlab/sqliter/native/NativeDatabaseConnection.kt

@@ -92,6 +92,7 @@ class NativeDatabaseConnection internal constructor(
     fun migrateIfNeeded(
         create: (DatabaseConnection) -> Unit,
         upgrade: (DatabaseConnection, Int, Int) -> Unit,
+        downgrade: (DatabaseConnection, Int, Int) -> Unit,
         version: Int
     ) {
         this.withTransaction {
@@ -100,10 +101,11 @@ class NativeDatabaseConnection internal constructor(
                 create(this)
                 setVersion(version)
             } else if (initialVersion != version) {
-                if (initialVersion > version)
-                    throw IllegalStateException("Database version $initialVersion newer than config version $version")
-
-                upgrade(this, initialVersion, version)
+                if (initialVersion > version) {
+                    downgrade(this, initialVersion, version)
+                } else {
+                    upgrade(this, initialVersion, version)
+                }
                 setVersion(version)
             }
         }

sqliter-driver/src/nativeCommonMain/kotlin/co/touchlab/sqliter/native/NativeDatabaseManager.kt

@@ -89,7 +89,7 @@ class NativeDatabaseManager(private val path:String,
                 try {
                     val version = configuration.version
                     if(version != NO_VERSION_CHECK)
-                        conn.migrateIfNeeded(configuration.create, configuration.upgrade, version)
+                        conn.migrateIfNeeded(configuration.create, configuration.upgrade, configuration.downgrade, version)
                 } catch (e: Exception) {
 
                     // If this failed, we have to close the connection or we will end up leaking it.

sqliter-driver/src/nativeCommonTest/kotlin/co/touchlab/sqliter/DatabaseManagerTest.kt

@@ -149,8 +149,7 @@ class DatabaseManagerTest : BaseDatabaseTest(){
     }
 
     @Test
-    fun downgradeNotAllowed(){
-        val upgradeCalled = AtomicInt(0)
+    fun downgradeNotAllowedByDefault() {
         val config1 = DatabaseConfiguration(
             name = TEST_DB_NAME,
             version = 1,
@@ -159,16 +158,11 @@ class DatabaseManagerTest : BaseDatabaseTest(){
                     execute()
                 }
             },
-            upgrade = { _, _, _ ->
-                upgradeCalled.increment()
-            },
             loggingConfig = DatabaseConfiguration.Logging(logger = NoneLogger),
         )
 
-        createDatabaseManager(config1).withConnection {  }
-        assertEquals(0, upgradeCalled.value)
-        createDatabaseManager(config1.copy(version = 2)).withConnection {  }
-        assertEquals(1, upgradeCalled.value)
+        createDatabaseManager(config1).withConnection { }
+        createDatabaseManager(config1.copy(version = 2)).withConnection { }
 
         var conn: DatabaseConnection? = null
         assertFails {
@@ -178,6 +172,40 @@ class DatabaseManagerTest : BaseDatabaseTest(){
         conn?.close()
     }
 
+    @Test
+    fun downgradeCalled() {
+        val upgradeCalled = AtomicInt(0)
+        val downgradeCalled = AtomicInt(0)
+        val config1 = DatabaseConfiguration(
+            name = TEST_DB_NAME,
+            version = 1,
+            create = { db ->
+                db.withStatement(TWO_COL) {
+                    execute()
+                }
+            },
+            upgrade = { _, _, _ ->
+                upgradeCalled.increment()
+            },
+            downgrade = { _, _, _ ->
+                downgradeCalled.increment()
+            },
+            loggingConfig = DatabaseConfiguration.Logging(logger = NoneLogger),
+        )
+
+        createDatabaseManager(config1).withConnection { }
+        assertEquals(0, upgradeCalled.value)
+        assertEquals(0, downgradeCalled.value)
+
+        createDatabaseManager(config1.copy(version = 2)).withConnection { }
+        assertEquals(1, upgradeCalled.value)
+        assertEquals(0, downgradeCalled.value)
+
+        createDatabaseManager(config1.copy(version = 1)).withConnection { }
+        assertEquals(1, upgradeCalled.value)
+        assertEquals(1, downgradeCalled.value)
+    }
+
     @Test
     fun failedCreateRollsBack(){
         val configFail = DatabaseConfiguration(