Added support for teacher column

app/src/main/java/com/denizd/substitutionplan/database/SubstDatabase.kt

@@ -4,10 +4,12 @@ import android.content.Context
 import androidx.room.Database
 import androidx.room.Room
 import androidx.room.RoomDatabase
+import androidx.room.migration.Migration
+import androidx.sqlite.db.SupportSQLiteDatabase
 import com.denizd.substitutionplan.models.Food
 import com.denizd.substitutionplan.models.Subst
 
-@Database(entities = [Subst::class, Food::class], version = 5, exportSchema = false)
+@Database(entities = [Subst::class, Food::class], version = 6, exportSchema = false)
 internal abstract class SubstDatabase : RoomDatabase() {
 
     abstract fun substDao(): SubstDao
@@ -15,6 +17,12 @@ internal abstract class SubstDatabase : RoomDatabase() {
     companion object {
 
         private var instance: SubstDatabase? = null
+        private val addTeacherColumn = object : Migration(5, 6) {
+            override fun migrate(database: SupportSQLiteDatabase) {
+                database.execSQL(
+                    "ALTER TABLE subst_table ADD COLUMN teacher TEXT NOT NULL DEFAULT ''")
+            }
+        }
 
         fun getInstance(context: Context): SubstDatabase? {
             if (instance == null) {
@@ -22,7 +30,7 @@ internal abstract class SubstDatabase : RoomDatabase() {
                     instance = Room.databaseBuilder(context.applicationContext,
                             SubstDatabase::class.java,
                             "subst_database")
-                            .fallbackToDestructiveMigration()
+                            .addMigrations(addTeacherColumn)
                             .build()
                 }
             }