GreenDao數(shù)據(jù)庫升級

第1步：升級數(shù)據(jù)庫版本號

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

android {
    ...
}

greendao{
    schemaVersion 2 // 版本號+1
}

dependencies {
    ...
}

第2步：修改數(shù)據(jù)庫實(shí)體類

@Entity
public class Person {

    @Id(autoincrement = true)
    private Long id;

    @NotNull
    private String name;

    private Integer age; // 增加一個年齡字段
｝

第3步：遷移數(shù)據(jù)庫

注：數(shù)據(jù)庫升級不可使用GreenDao默認(rèn)生成的DaoMaster.DevOpenHelper，因為DaoMaster.DevOpenHelper在數(shù)據(jù)庫升級時會刪除數(shù)據(jù)庫再重新創(chuàng)建。

因此，我們需要繼承DaoMaster.OpenHelper實(shí)現(xiàn)自己的MyOpenHelper，在onUpgrade()方法中升級數(shù)據(jù)庫。

// 繼承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);
        // 遷移數(shù)據(jù)庫(如果修改了多個實(shí)體類，則需要把對應(yīng)的Dao都傳進(jìn)來)
        MigrationHelper.migrate(db, PersonDao.class);
    }
}

重新編譯并運(yùn)行工程，即可完成數(shù)據(jù)庫升級。

Migration Helper class

1. The class catch all the Daos that you got
2. Creates the temporary tables based on the old version's scheme (generateTempTables method)
3. Import all the data to this new tables (generateTempTables method)
4. Drop all the tables of the old version (DaoMaster.dropAllTables method)
5. Creates the tables of the new version (DaoMaster.createAllTables method)
6. Updates the new version's tables from the temporaries (restoreData method)
7. Drop all temporary tables (restoreData method)

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.annotation.NonNull;
import android.text.TextUtils;

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.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * 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;
    }

}

參考資料：GreenDAO schema update and data migration?