Greendao 数据库升级解决方案

1. APP开发期间的数据库改动（APP未上线）
   直接上DaoMaster的代码

/*** WARNING: Drops all table on Upgrade! Use only during development. */public static class DevOpenHelper extends OpenHelper {        public DevOpenHelper(Context context, String name, CursorFactory factory) {            super(context, name, factory);        }        @Override        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {            Log.i("greenDAO", "Upgrading schema from version " + oldVersion + " to " + newVersion + " by dropping all tables");            dropAllTables(db, true);            onCreate(db);        }    }

注意看第一行注释：WARNING: Drops all table on Upgrade! Use only during development.

数据库升级的话，会删除所有表,然后重新创建。这种方式在开发期间，APP还没有上线之前是可以的。
当APP上线后，我们不能使用这种方式，因为这样会导致已经存在的数据会被删除。

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2.APP上线后,数据库升级

需要我们写一个类来实现OpenHelper

1.我们自己实现了onUpgrade 方法来自定义升级过程。

2.当然升级过程中也要修改DaoMaster.SCHEMA_VERSION

3.当DaoMaster.SCHEMA_VERSION 跟你当前数据库的版本比较后, 会根据你当前数据库的版本，然后进行升级。
4.关键代码onUpgrade 方法,会比较新数据库和旧数据库的版本,然后执行相应的sql升级：

 @Override    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {        LogUtil.w(SQLiteOpenHelper.class.getSimpleName(), "Upgrade from" + oldVersion + "to" + newVersion);        SortedMap<Integer, Migration> migrations = ALL_MIGRATIONS.subMap(oldVersion, newVersion);        executeMigrations(sqLiteDatabase, migrations.keySet());    }    private void executeMigrations(final SQLiteDatabase paramSQLiteDatabase, final Set<Integer> migrationVersions) {        for (final Integer version : migrationVersions) {            ALL_MIGRATIONS.get(version).migrate(paramSQLiteDatabase);        }    }

最后，推荐一个国外大神封装的Greendao上线后数据库升级的工具类

import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.support.annotation.NonNull;import android.text.TextUtils;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.Arrays;import java.util.List;import de.greenrobot.dao.AbstractDao;import de.greenrobot.dao.database.Database;import de.greenrobot.dao.database.StandardDatabase;import de.greenrobot.dao.internal.DaoConfig;/** * Createdby PedroOkawa and modified by MBH on 16/08/16. */public final class MigrationHelper {    public static void migrate(SQLiteDatabase sqliteDatabase, Class<? extends AbstractDao<?, ?>>... daoClasses) {        StandardDatabase db = new StandardDatabase(sqliteDatabase);        generateNewTablesIfNotExists(db, daoClasses);        generateTempTables(db, daoClasses);        dropAllTables(db, true, daoClasses);        createAllTables(db, false, daoClasses);        restoreData(db, daoClasses);    }    public static void migrate(StandardDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {        generateNewTablesIfNotExists(db, daoClasses);        generateTempTables(db, daoClasses);        dropAllTables(db, true, daoClasses);        createAllTables(db, false, daoClasses);        restoreData(db, daoClasses);    }    private static void generateNewTablesIfNotExists(StandardDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {        reflectMethod(db, "createTable", true, daoClasses);    }    private static void generateTempTables(StandardDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {        for (int i = 0; i < daoClasses.length; i++) {            DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);            String tableName = daoConfig.tablename;            String tempTableName = daoConfig.tablename.concat("_TEMP");            StringBuilder insertTableStringBuilder = new StringBuilder();            insertTableStringBuilder.append("CREATE TEMP TABLE ").append(tempTableName);            insertTableStringBuilder.append(" AS SELECT * FROM ").append(tableName).append(";");            db.execSQL(insertTableStringBuilder.toString());        }    }    private static void dropAllTables(StandardDatabase db, boolean ifExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {        reflectMethod(db, "dropTable", ifExists, daoClasses);    }    private static void createAllTables(StandardDatabase db, boolean ifNotExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {        reflectMethod(db, "createTable", ifNotExists, daoClasses);    }    /**     * dao class already define the sql exec method, so just invoke it     */    private static void reflectMethod(StandardDatabase db, String methodName, boolean isExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {        if (daoClasses.length < 1) {            return;        }        try {            for (Class cls : daoClasses) {                Method method = cls.getDeclaredMethod(methodName, Database.class, boolean.class);                method.invoke(null, db, isExists);            }        } catch (NoSuchMethodException e) {            e.printStackTrace();        } catch (InvocationTargetException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        }    }    private static void restoreData(StandardDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {        for (int i = 0; i < daoClasses.length; i++) {            DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);            String tableName = daoConfig.tablename;            String tempTableName = daoConfig.tablename.concat("_TEMP");            // get all columns from tempTable, take careful to use the columns list            List<String> columns = getColumns(db, tempTableName);            ArrayList<String> properties = new ArrayList<>(columns.size());            for (int j = 0; j < daoConfig.properties.length; j++) {                String columnName = daoConfig.properties[j].columnName;                if (columns.contains(columnName)) {                    properties.add(columnName);                }            }            if (properties.size() > 0) {                final String columnSQL = TextUtils.join(",", properties);                StringBuilder insertTableStringBuilder = new StringBuilder();                insertTableStringBuilder.append("INSERT INTO ").append(tableName).append(" (");                insertTableStringBuilder.append(columnSQL);                insertTableStringBuilder.append(") SELECT ");                insertTableStringBuilder.append(columnSQL);                insertTableStringBuilder.append(" FROM ").append(tempTableName).append(";");                db.execSQL(insertTableStringBuilder.toString());            }            StringBuilder dropTableStringBuilder = new StringBuilder();            dropTableStringBuilder.append("DROP TABLE ").append(tempTableName);            db.execSQL(dropTableStringBuilder.toString());        }    }    private static List<String> getColumns(StandardDatabase db, String tableName) {        List<String> columns = null;        Cursor cursor = null;        try {            cursor = db.rawQuery("SELECT * FROM " + tableName + " limit 0", null);            if (null != cursor && cursor.getColumnCount() > 0) {                columns = Arrays.asList(cursor.getColumnNames());            }        } catch (Exception e) {            e.printStackTrace();        } finally {            if (cursor != null)                cursor.close();            if (null == columns)                columns = new ArrayList<>();        }        return columns;    }}

用法是这样

@Overridepublic void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {    MigrationHelper.migrate(new StandardDatabase(sqLiteDatabase),                UserDao.class,                ItemDao.class);    // OR you can use it like this (Dont use both it is example of 2 different usages)    MigrationHelper.migrate(sqLiteDatabase,                UserDao.class,                ItemDao.class);}

StandardDatabase 可以在greendao里面导入。