GreenDao数据库升级

第一步:升级数据库版本号
首先存在着数据库 并且版本号只能高不能低

// app:build.gradle
apply plugin: 'com.android.application'
apply plugin: 'org.greenrobot.greendao'

android {
    ...
}

greendao{
    schemaVersion 2 // 版本号+1
}

dependencies {
    ...
}

第2步：修改数据库对应的实体类
在原有的基础上 增 删 改(字段,类型,权限)

@Entity
public class Person {

    @Id(autoincrement = true)
    private Long id;

    @NotNull
    private String name;

    private Integer age; // 增加一个年龄字段
｝

第3步：自定义OpenHelper对象
自定义一个类去继承DaoMaster.OpenHelper重写数据库的升级方法onUpgrade() 代码如下

// 继承DaoMaster.OpenHelper
public class MyOpenHelper extends DaoMaster.OpenHelper {

    public MyOpenHelper(Context context, String name) {
        super(context, name);
    }

    public MyOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
        super(context, name, factory);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        super.onUpgrade(db, oldVersion, newVersion);
        // 升级数据库
        MigrationHelper.migrate(db, PersonDao.class);
    }
}

第4步：替换默认的DevOpenHelper
将之前版本中的DaoMaster.OpenHelper替换为我们重写后的OpenHelper 其他的不用改变

private DaoSession initGreenDao() {
    // 替换为自定义的OpenHelper对象
    DaoMaster.OpenHelper openHelper = new MyOpenHelper(this, "cumulus.db");
    SQLiteDatabase database = openHelper.getReadableDatabase();
    DaoMaster daoMaster = new DaoMaster(database);
    return daoMaster.newSession();
}

可以同时升级多张表

升级工具类
1.根据旧版本的方案（generateTempTables方法）创建临时表
2.将所有数据导入此新表（generateTempTables方法）
3.删除旧版本的所有表（DaoMaster.dropAllTables方法）
4.创建新版本的表（DaoMaster.createAllTables方法）
5.从临时更新新版本的表（restoreData方法）
6.删除所有临时表（restoreData方法）

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.text.TextUtils;
import android.util.Log;

import com.crashlytics.android.Crashlytics;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import de.greenrobot.dao.AbstractDao;
import de.greenrobot.dao.internal.DaoConfig;
import greendao.DaoMaster;


/**
 * Created by pokawa on 18/05/15.
 */
public class MigrationHelper {

    private static final String CONVERSION_CLASS_NOT_FOUND_EXCEPTION = "MIGRATION HELPER - CLASS DOESN'T MATCH WITH THE CURRENT PARAMETERS";
    private static MigrationHelper instance;

    public static MigrationHelper getInstance() {
        if(instance == null) {
            instance = new MigrationHelper();
        }
        return instance;
    }

    public void migrate(SQLiteDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
        generateTempTables(db, daoClasses);
        DaoMaster.dropAllTables(db, true);
        DaoMaster.createAllTables(db, false);
        restoreData(db, daoClasses);
    }

    private void generateTempTables(SQLiteDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
        for(int i = 0; i < daoClasses.length; i++) {
            DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);

            String divider = "";
            String tableName = daoConfig.tablename;
            String tempTableName = daoConfig.tablename.concat("_TEMP");
            ArrayList<String> properties = new ArrayList<>();

            StringBuilder createTableStringBuilder = new StringBuilder();

            createTableStringBuilder.append("CREATE TABLE ").append(tempTableName).append(" (");

            for(int j = 0; j < daoConfig.properties.length; j++) {
                String columnName = daoConfig.properties[j].columnName;

                if(getColumns(db, tableName).contains(columnName)) {
                    properties.add(columnName);

                    String type = null;

                    try {
                        type = getTypeByClass(daoConfig.properties[j].type);
                    } catch (Exception exception) {
                        Crashlytics.logException(exception);
                    }

                    createTableStringBuilder.append(divider).append(columnName).append(" ").append(type);

                    if(daoConfig.properties[j].primaryKey) {
                        createTableStringBuilder.append(" PRIMARY KEY");
                    }

                    divider = ",";
                }
            }
            createTableStringBuilder.append(");");

            db.execSQL(createTableStringBuilder.toString());

            StringBuilder insertTableStringBuilder = new StringBuilder();

            insertTableStringBuilder.append("INSERT INTO ").append(tempTableName).append(" (");
            insertTableStringBuilder.append(TextUtils.join(",", properties));
            insertTableStringBuilder.append(") SELECT ");
            insertTableStringBuilder.append(TextUtils.join(",", properties));
            insertTableStringBuilder.append(" FROM ").append(tableName).append(";");

            db.execSQL(insertTableStringBuilder.toString());
        }
    }

    private void restoreData(SQLiteDatabase 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");
            ArrayList<String> properties = new ArrayList();

            for (int j = 0; j < daoConfig.properties.length; j++) {
                String columnName = daoConfig.properties[j].columnName;

                if(getColumns(db, tempTableName).contains(columnName)) {
                    properties.add(columnName);
                }
            }

            StringBuilder insertTableStringBuilder = new StringBuilder();

            insertTableStringBuilder.append("INSERT INTO ").append(tableName).append(" (");
            insertTableStringBuilder.append(TextUtils.join(",", properties));
            insertTableStringBuilder.append(") SELECT ");
            insertTableStringBuilder.append(TextUtils.join(",", properties));
            insertTableStringBuilder.append(" FROM ").append(tempTableName).append(";");

            StringBuilder dropTableStringBuilder = new StringBuilder();

            dropTableStringBuilder.append("DROP TABLE ").append(tempTableName);

            db.execSQL(insertTableStringBuilder.toString());
            db.execSQL(dropTableStringBuilder.toString());
        }
    }

    private String getTypeByClass(Class<?> type) throws Exception {
        if(type.equals(String.class)) {
            return "TEXT";
        }
        if(type.equals(Long.class) || type.equals(Integer.class) || type.equals(long.class)) {
            return "INTEGER";
        }
        if(type.equals(Boolean.class)) {
            return "BOOLEAN";
        }

        Exception exception = new Exception(CONVERSION_CLASS_NOT_FOUND_EXCEPTION.concat(" - Class: ").concat(type.toString()));
        Crashlytics.logException(exception);
        throw exception;
    }

    private static List<String> getColumns(SQLiteDatabase db, String tableName) {
        List<String> columns = new ArrayList<>();
        Cursor cursor = null;
        try {
            cursor = db.rawQuery("SELECT * FROM " + tableName + " limit 1", null);
            if (cursor != null) {
                columns = new ArrayList<>(Arrays.asList(cursor.getColumnNames()));
            }
        } catch (Exception e) {
            Log.v(tableName, e.getMessage(), e);
            e.printStackTrace();
        } finally {
            if (cursor != null)
                cursor.close();
        }
        return columns;
    }
}

这是一个如何在DaoMaster.java类中调用它的示例：

@Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.i("greenDAO", "Upgrading schema from version " + oldVersion + " to " + newVersion + " by migrating all tables data");

        MigrationHelper.getInstance().migrate(db,
                UserDao.class,
                ItemDao.class);
    }