GreenDao升级详解

数据库升级嘛，就是在原有版本的基础上进行增之类的操作

实际升级不难，下面就是GreenDao升级的小详解哈，看完就懂喽~~~~~

1.新建MigrationHelper 类

import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.support.annotation.NonNull;
import android.text.TextUtils;
import android.util.Log;
 
import org.greenrobot.greendao.AbstractDao;
import org.greenrobot.greendao.database.Database;
import org.greenrobot.greendao.database.StandardDatabase;
import org.greenrobot.greendao.internal.DaoConfig;
 
import java.lang.ref.WeakReference;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
 
/**
 *
 * please call {@link #migrate(SQLiteDatabase, Class[])} or {@link #migrate(Database, Class[])}
 *
 */
public final class MigrationHelper {
 
    public static boolean DEBUG = false;
    private static String TAG = "MigrationHelper";
    private static final String SQLITE_MASTER = "sqlite_master";
    private static final String SQLITE_TEMP_MASTER = "sqlite_temp_master";
 
    private static WeakReference<ReCreateAllTableListener> weakListener;
 
    public interface ReCreateAllTableListener{
        void onCreateAllTables(Database db, boolean ifNotExists);
        void onDropAllTables(Database db, boolean ifExists);
    }
 
    public static void migrate(SQLiteDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
        printLog("【The Old Database Version】" + db.getVersion());
        Database database = new StandardDatabase(db);
        migrate(database, daoClasses);
    }
 
    public static void migrate(SQLiteDatabase db, ReCreateAllTableListener listener, Class<? extends AbstractDao<?, ?>>... daoClasses) {
        weakListener = new WeakReference<>(listener);
        migrate(db, daoClasses);
    }
 
    public static void migrate(Database database, ReCreateAllTableListener listener, Class<? extends AbstractDao<?, ?>>... daoClasses) {
        weakListener = new WeakReference<>(listener);
        migrate(database, daoClasses);
    }
 
    public static void migrate(Database database, Class<? extends AbstractDao<?, ?>>... daoClasses) {
        printLog("【Generate temp table】start");
        generateTempTables(database, daoClasses);
        printLog("【Generate temp table】complete");
 
        ReCreateAllTableListener listener = null;
        if (weakListener != null) {
            listener = weakListener.get();
        }
 
        if (listener != null) {
            listener.onDropAllTables(database, true);
            printLog("【Drop all table by listener】");
            listener.onCreateAllTables(database, false);
            printLog("【Create all table by listener】");
        } else {
            dropAllTables(database, true, daoClasses);
            createAllTables(database, false, daoClasses);
        }
        printLog("【Restore data】start");
        restoreData(database, daoClasses);
        printLog("【Restore data】complete");
    }
 
    private static void generateTempTables(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
        for (int i = 0; i < daoClasses.length; i++) {
            String tempTableName = null;
            DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);
            String tableName = daoConfig.tablename;
            if (!isTableExists(db, false, tableName)) {
                printLog("【New Table】" + tableName);
                continue;
            }
            try {
                tempTableName = daoConfig.tablename.concat("_TEMP");
                StringBuilder dropTableStringBuilder = new StringBuilder();
                dropTableStringBuilder.append("DROP TABLE IF EXISTS ").append(tempTableName).append(";");
                db.execSQL(dropTableStringBuilder.toString());
                StringBuilder insertTableStringBuilder = new StringBuilder();
                insertTableStringBuilder.append("CREATE TEMPORARY TABLE ").append(tempTableName);
                insertTableStringBuilder.append(" AS SELECT * FROM ").append(tableName).append(";");
                db.execSQL(insertTableStringBuilder.toString());
                printLog("【Table】" + tableName +"\n ---Columns-->"+getColumnsStr(daoConfig));
                printLog("【Generate temp table】" + tempTableName);
            } catch (SQLException e) {
                Log.e(TAG, "【Failed to generate temp table】" + tempTableName, e);
            }
        }
    }
 
    private static boolean isTableExists(Database db, boolean isTemp, String tableName) {
        if (db == null || TextUtils.isEmpty(tableName)) {
            return false;
        }
        String dbName = isTemp ? SQLITE_TEMP_MASTER : SQLITE_MASTER;
        String sql = "SELECT COUNT(*) FROM " + dbName + " WHERE type = ? AND name = ?";
        Cursor cursor=null;
        int count = 0;
        try {
            cursor = db.rawQuery(sql, new String[]{"table", tableName});
            if (cursor == null || !cursor.moveToFirst()) {
                return false;
            }
            count = cursor.getInt(0);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (cursor != null)
                cursor.close();
        }
        return count > 0;
    }
 
 
    private static String getColumnsStr(DaoConfig daoConfig) {
        if (daoConfig == null) {
            return "no columns";
        }
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < daoConfig.allColumns.length; i++) {
            builder.append(daoConfig.allColumns[i]);
            builder.append(",");
        }
        if (builder.length() > 0) {
            builder.deleteCharAt(builder.length() - 1);
        }
        return builder.toString();
    }
 
 
    private static void dropAllTables(Database db, boolean ifExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
        reflectMethod(db, "dropTable", ifExists, daoClasses);
        printLog("【Drop all table by reflect】");
    }
 
    private static void createAllTables(Database db, boolean ifNotExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
        reflectMethod(db, "createTable", ifNotExists, daoClasses);
        printLog("【Create all table by reflect】");
    }
 
    /**
     * dao class already define the sql exec method, so just invoke it
     */
    private static void reflectMethod(Database 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(Database 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");
            if (!isTableExists(db, true, tempTableName)) {
                continue;
            }
            try {
                // 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("REPLACE INTO ").append(tableName).append(" (");
                    insertTableStringBuilder.append(columnSQL);
                    insertTableStringBuilder.append(") SELECT ");
                    insertTableStringBuilder.append(columnSQL);
                    insertTableStringBuilder.append(" FROM ").append(tempTableName).append(";");
                    db.execSQL(insertTableStringBuilder.toString());
                    printLog("【Restore data】 to " + tableName);
                }
                StringBuilder dropTableStringBuilder = new StringBuilder();
                dropTableStringBuilder.append("DROP TABLE ").append(tempTableName);
                db.execSQL(dropTableStringBuilder.toString());
                printLog("【Drop temp table】" + tempTableName);
            } catch (SQLException e) {
                Log.e(TAG, "【Failed to restore data from temp table 】" + tempTableName, e);
            }
        }
    }
 
    private static List<String> getColumns(Database 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;
    }
 
    private static void printLog(String info){
        if(DEBUG){
            Log.d(TAG, info);
        }
    }
 

2.新建MyOpenHelper类

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
 
import com.example.lenovo.greendao.Dao.DaoMaster;
import com.example.lenovo.greendao.Dao.StudentDao;
 
import org.greenrobot.greendao.database.Database;
 
public class MyOpenHelper extends DaoMaster.OpenHelper {
    public MyOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
        super(context, name, factory);
    }
 
    @Override
    public void onUpgrade(Database db, int oldVersion, int newVersion) {
 
        //把需要管理的数据库表DAO作为最后一个参数传入到方法中
        MigrationHelper.migrate(db, new MigrationHelper.ReCreateAllTableListener() {
 
            @Override
            public void onCreateAllTables(Database db, boolean ifNotExists) {
                DaoMaster.createAllTables(db, ifNotExists);
            }
 
            @Override
            public void onDropAllTables(Database db, boolean ifExists) {
                DaoMaster.dropAllTables(db, ifExists);
 
 
 
 
            }
        },  StudentDao.class);
    }
}
 
 

3.版本号在j升级时进行修改

greendao {
    //数据库版本号，升级时进行修改
    schemaVersion 2
 
    daoPackage 'com.dev.base.model.db'
    targetGenDir 'src/main/java'
}

4.在表实体中，调整其中的变量（表字段），一般就是新增/删除/修改字段。

注意！！！！：

1）新增的字段或修改的字段，其变量类型应使用基础数据类型的包装类，如使用Integer而不是int，避免升级过程中报错。
2）根据MigrationHelper中的代码，升级后，新增的字段和修改的字段，都会默认被赋予null值。

将原有

DaoSession daoSession = DaoMaster.newDevSession(this, Student    Dao.TABLENAME);
    dao = daoSession.getStudentDao();

替换为

MyOpenHelper myOpenHelper = new MyOpenHelper(this, StudentDao.TABLENAME, null);//建库
        DaoMaster daoMaster = new DaoMaster(myOpenHelper.getWritableDatabase());
        DaoSession daoSession = daoMaster.newSession();
        studentDao = daoSession.getStudentDao();
        studentDao.insert(new Student(null, "天地", 123,"sdsdsd"))
//        dao.insertOrReplace(new Student(null, "天地", 123);