GreenDao3+ 升级

给数据库添加一个字段：

通常只需要在对应的表(实体类）中添加想要的字段，然后如图操作!

即Rebuild Project ，再将 schemaVersion 进行修改即可即可。
这种方式的问题会将历史数据全部删除，包括其他未修改的表，可能是重新创建新的数据库吧。除非不需要历史数据，否则无法采用这种方式。

在使用Sqlite3的时候我们通常都是自定义 helper 类通过 onCreate 方法初始化，通过 onUpgrade()方法进行更新的，同理 GreenDao这里也可以使用这个方法，但是没办法直接使用sql 语句alter去添加字段，可能是因为关系型数据库的原因吧，具体没深入了解，但是我们依然可以通过 onUpgrade(）在生级的时候会被执行的特点来进行数据库升级。

1.自定义 helper

public class DBHelper extends DaoMaster.OpenHelper {

    public DBHelper(Context context, String name) {

        super(context, name);

    }

    @Override

    public void onUpgrade(Database db, int oldVersion, int newVersion) {

        super.onUpgrade(db, oldVersion, newVersion);//有人说要去掉这句，但是我没发现有问题，如果有问题可以去掉试一试

        if(oldVersion<newVersion){

            MigrationHelper.getInstance().migrate(db,AnimalDao.class,PersonDao.class);//重点在这里 国外大神封装的一个类，具体逻辑就是创建临时库记录原始数据，然后将数据copy 到新库中
//[https://stackoverflow.com/questions/13373170/greendao-schema-update-and-data-migration/30334668#30334668](https://stackoverflow.com/questions/13373170/greendao-schema-update-and-data-migration/30334668#30334668)


        }

    }

}

MigrationHelper 类

package com.green.dao;

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

import com.greendao.gen.DaoMaster;

import org.greenrobot.greendao.AbstractDao;
import org.greenrobot.greendao.database.Database;
import org.greenrobot.greendao.internal.DaoConfig;

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

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

    private void generateTempTables(Database 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) {
                    }

                    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(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");
            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()));
        throw exception;
    }

    private static List<String> getColumns(Database 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;
    }
}

创建数据库改为：

DBHelper openHelper =new DBHelper(App.getInstance(),"test");//改为调用自定义的helper

  daoMaster =new DaoMaster(openHelper.getWritableDatabase());

daoSession =daoMaster.newSession();

如果是数据量比较大的时候这种方式应该不是特别好吧