GreenDao3+ 升級

給數(shù)據(jù)庫添加一個字段：

通常只需要在對應(yīng)的表(實體類）中添加想要的字段吩蔑，然后如圖操作!

即Rebuild Project 嚎莉，再將 schemaVersion 進(jìn)行修改即可即可铃将。
這種方式的問題會將歷史數(shù)據(jù)全部刪除名段，包括其他未修改的表炕舵，可能是重新創(chuàng)建新的數(shù)據(jù)庫吧拄查。除非不需要歷史數(shù)據(jù)豪娜，否則無法采用這種方式餐胀。

在使用Sqlite3的時候我們通常都是自定義 helper 類通過 onCreate 方法初始化，通過 onUpgrade()方法進(jìn)行更新的瘤载，同理 GreenDao這里也可以使用這個方法骂澄，但是沒辦法直接使用sql 語句alter去添加字段，可能是因為關(guān)系型數(shù)據(jù)庫的原因吧惕虑，具體沒深入了解坟冲，但是我們依然可以通過 onUpgrade(）在生級的時候會被執(zhí)行的特點來進(jìn)行數(shù)據(jù)庫升級磨镶。

1.自定義 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);//有人說要去掉這句，但是我沒發(fā)現(xiàn)有問題健提，如果有問題可以去掉試一試

        if(oldVersion<newVersion){

            MigrationHelper.getInstance().migrate(db,AnimalDao.class,PersonDao.class);//重點在這里 國外大神封裝的一個類琳猫，具體邏輯就是創(chuàng)建臨時庫記錄原始數(shù)據(jù)，然后將數(shù)據(jù)copy 到新庫中
//[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 類

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;
    }
}

創(chuàng)建數(shù)據(jù)庫改為：

DBHelper openHelper =new DBHelper(App.getInstance(),"test");//改為調(diào)用自定義的helper

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

daoSession =daoMaster.newSession();

如果是數(shù)據(jù)量比較大的時候這種方式應(yīng)該不是特別好吧