Updated AndroidX

app/src/main/java/androidx/room/Migration.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package androidx.room.migration;
+
+import androidx.annotation.NonNull;
+import androidx.sqlite.db.SupportSQLiteDatabase;
+
+/**
+ * Base class for a database migration.
+ * <p>
+ * Each migration can move between 2 versions that are defined by {@link #startVersion} and
+ * {@link #endVersion}.
+ * <p>
+ * A migration can handle more than 1 version (e.g. if you have a faster path to choose when
+ * going version 3 to 5 without going to version 4). If Room opens a database at version
+ * 3 and latest version is &gt;= 5, Room will use the migration object that can migrate from
+ * 3 to 5 instead of 3 to 4 and 4 to 5.
+ * <p>
+ * If there are not enough migrations provided to move from the current version to the latest
+ * version, Room will clear the database and recreate so even if you have no changes between 2
+ * versions, you should still provide a Migration object to the builder.
+ */
+public abstract class Migration {
+    public final int startVersion;
+    public final int endVersion;
+
+    /**
+     * Creates a new migration between {@code startVersion} and {@code endVersion}.
+     *
+     * @param startVersion The start version of the database.
+     * @param endVersion The end version of the database after this migration is applied.
+     */
+    public Migration(int startVersion, int endVersion) {
+        this.startVersion = startVersion;
+        this.endVersion = endVersion;
+    }
+
+    /**
+     * Should run the necessary migrations.
+     * <p>
+     * This class cannot access any generated Dao in this method.
+     * <p>
+     * This method is already called inside a transaction and that transaction might actually be a
+     * composite transaction of all necessary {@code Migration}s.
+     *
+     * @param database The database instance
+     */
+    public abstract void migrate(@NonNull SupportSQLiteDatabase database);
+}