greendao3.0以上使用步驟(二):資料庫到底該怎麼升級
這一篇看看資料庫到底該怎麼升級呢?看我升級後的效果
沒有升級前的頁面顯示
沒有升級前的資料庫
- 升級後的頁面顯示
- 升級後的資料庫
看增加了一個NUM欄位 。
最新有小夥伴遇到資料庫升級問題了,說網上都是2.0版本的升級方法,自己使用的是3.0,沒法升級資料庫了….
然後問別人,別人讓他改為2.0版本,讓資料庫裡面有兩個表供應用操作,天啦這還了得,我用的也是3.0,那以後還得了,非把人累死……..
資料庫的升級大家都知道,建立臨時表,進行過渡儲存而已,網上有人提供了一個MigrationHelper類,真好正好可以使用!
but 蹦出了這樣一個大bug,請看:
什麼新增欄位不能為空? 我沒有設定呀,到底為什麼呢?
我相信有的小夥伴也遇到過吧!那下面我們一起來看看怎麼回事吧
思路:
建立臨時表-->刪除原表-->建立新表-->複製臨時表資料到新表並刪除臨時表;這樣資料庫表的更新就完成了
- 首先我們引入MigrationHelper類,內容如下:
package cn.hnshangyu.testgreendao.helper;
import android.database.Cursor;
import android.text.TextUtils;
import android.util.Log;
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;
import cn.hnshangyu.testgreendao.greendao.DaoMaster;
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);
}
/**
* 生成臨時列表
*
* @param db
* @param 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) {
exception.printStackTrace();
}
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());
}
}
/**
* 儲存新的資料庫表 以及資料
*
* @param db
* @param daoClasses
*/
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()));
exception.printStackTrace();
throw exception;
}
private 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;
}
}
- 然後需要知道資料庫更新表的方法是DaoMaster類中的onUpgrade方法:
注意:
這個類為配置greendao後系統自動生成,不能直接在這裡操作,不然每次執行此類都是重新生成的。
- 構建MyOpenHelper幫助類,重寫onUpgrade方法進行操作:
package cn.hnshangyu.testgreendao.helper;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
import org.greenrobot.greendao.database.Database;
import cn.hnshangyu.testgreendao.greendao.DaoMaster;
import cn.hnshangyu.testgreendao.greendao.StudentDao;
public class MyOpenHelper extends DaoMaster.OpenHelper {
public MyOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
super(context, name, factory);
}
/**
* 資料庫升級
* @param db
* @param oldVersion
* @param newVersion
*/
@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
//操作資料庫的更新 有幾個表升級都可以傳入到下面
MigrationHelper.getInstance().migrate(db,StudentDao.class);
}
}
- 什麼地方使用MyOpenHelper 類呢?
之前的greendao3.0以上使用步驟(一)中,我建立了一個DbManager管理類來進行對資料庫的統一管理,今天同樣使用這個類:
那麼與之前的有什麼區別呢??
其實就是在獲取DaoMaster時有所改變,開啟資料庫方式不同
1、之前的方法
/**
* 獲取DaoMaster
*
* @param context
* @return
*/
public static DaoMaster getDaoMaster(Context context) {
if (null == mDaoMaster) {
synchronized (DbManager.class) {
if (null == mDaoMaster) {
mDaoMaster = new DaoMaster(getWritableDatabase(context));
}
}
}
return mDaoMaster;
}
2、現在的
/**
* 獲取DaoMaster
*
* 判斷是否存在資料庫,如果沒有則建立資料庫
* @param context
* @return
*/
public static DaoMaster getDaoMaster(Context context) {
if (null == mDaoMaster) {
synchronized (DbManager.class) {
if (null == mDaoMaster) {
MyOpenHelper helper = new MyOpenHelper(context,DB_NAME,null);
mDaoMaster = new DaoMaster(helper.getWritableDatabase());
}
}
}
return mDaoMaster;
}
3、整個類的類容:
package cn.hnshangyu.testgreendao.db;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import cn.hnshangyu.testgreendao.greendao.DaoMaster;
import cn.hnshangyu.testgreendao.greendao.DaoSession;
import cn.hnshangyu.testgreendao.helper.MyOpenHelper;
public class DbManager {
// 是否加密
public static final boolean ENCRYPTED = true;
private static final String DB_NAME = "test.db";
private static DbManager mDbManager;
private static DaoMaster.DevOpenHelper mDevOpenHelper;
private static DaoMaster mDaoMaster;
private static DaoSession mDaoSession;
private Context mContext;
private DbManager(Context context) {
this.mContext = context;
// 初始化資料庫資訊
mDevOpenHelper = new DaoMaster.DevOpenHelper(context, DB_NAME);
getDaoMaster(context);
getDaoSession(context);
}
public static DbManager getInstance(Context context) {
if (null == mDbManager) {
synchronized (DbManager.class) {
if (null == mDbManager) {
mDbManager = new DbManager(context);
}
}
}
return mDbManager;
}
/**
* 獲取可讀資料庫
*
* @param context
* @return
*/
public static SQLiteDatabase getReadableDatabase(Context context) {
if (null == mDevOpenHelper) {
getInstance(context);
}
return mDevOpenHelper.getReadableDatabase();
}
/**
* 獲取可寫資料庫
*
* @param context
* @return
*/
public static SQLiteDatabase getWritableDatabase(Context context) {
if (null == mDevOpenHelper) {
getInstance(context);
}
return mDevOpenHelper.getWritableDatabase();
}
/**
* 獲取DaoMaster
*
* 判斷是否存在資料庫,如果沒有則建立資料庫
* @param context
* @return
*/
public static DaoMaster getDaoMaster(Context context) {
if (null == mDaoMaster) {
synchronized (DbManager.class) {
if (null == mDaoMaster) {
MyOpenHelper helper = new MyOpenHelper(context,DB_NAME,null);
mDaoMaster = new DaoMaster(helper.getWritableDatabase());
}
}
}
return mDaoMaster;
}
/**
* 獲取DaoMaster
*
* @param context
* @return
*/
// public static DaoMaster getDaoMaster(Context context) {
// if (null == mDaoMaster) {
// synchronized (DbManager.class) {
// if (null == mDaoMaster) {
//
// mDaoMaster = new DaoMaster(getWritableDatabase(context));
// }
// }
// }
// return mDaoMaster;
// }
/**
* 獲取DaoSession
*
* @param context
* @return
*/
public static DaoSession getDaoSession(Context context) {
if (null == mDaoSession) {
synchronized (DbManager.class) {
mDaoSession = getDaoMaster(context).newSession();
}
}
return mDaoSession;
}
}
- 現在我們在bean物件裡面加一個num欄位,注意型別:
package cn.hnshangyu.testgreendao.bean;
import org.greenrobot.greendao.annotation.Entity;
import org.greenrobot.greendao.annotation.Id;
import org.greenrobot.greendao.annotation.Keep;
import org.greenrobot.greendao.annotation.Generated;
import org.greenrobot.greendao.annotation.NotNull;
@Entity(generateConstructors = false)
public class Student {
@Id
private Long id;
private String name;
private int age;
private int num;
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", age=" + age +
", num=" + num +
'}';
}
public Student() {
}
@Keep
public Student(String name, int age) {
this.name = name;
this.age = age;
}
public Student(Long id, String name, int age) {
this.id = id;
this.name = name;
this.age = age;
}
@Keep
public Long getId() {
return id;
}
@Keep
public void setId(Long id) {
this.id = id;
}
@Keep
public String getName() {
return name;
}
@Keep
public void setName(String name) {
this.name = name;
}
@Keep
public int getAge() {
return age;
}
@Keep
public void setAge(int age) {
this.age = age;
}
@Keep
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof Student)) return false;
Student student = (Student) o;
return name.equals(student.name);
}
@Keep
@Override
public int hashCode() {
return (int) (id ^ (id >>> 32));
}
}
大家看到了我加了一個int型別的欄位
- 最後就是升級版本了,在build升級版本
版本升為2了,同步一下
然後執行程式………
哎呀!你會發現報了一個重大bug,就是開始我提到的新增欄位不能為空,這是為什麼呢?bean物件中我沒有限定不能為空啊!
好吧我們看看怎麼回事吧!
- 首先他報錯的部位為MigrationHelper的restoreData方法,把新臨時表資料拷貝到新表中
- 既然欄位不能為空,大部分是因為建立表的時候造成的
MigrationHelper建立表的時候呼叫的是DaoMaster的createAllTables方法:
/** Creates underlying database table using DAOs. */
public static void createAllTables(Database db, boolean ifNotExists) {
StudentDao.createTable(db, ifNotExists);
}
從greendao生成的原始碼中可以看到呼叫的是StudentDao的createTable方法
那麼在StudentDao中:
/** Creates the underlying database table. */
public static void createTable(Database db, boolean ifNotExists) {
String constraint = ifNotExists? "IF NOT EXISTS ": "";
db.execSQL("CREATE TABLE " + constraint + "\"STUDENT\" (" + //
"\"_id\" INTEGER PRIMARY KEY ," + // 0: id
"\"NAME\" TEXT," + // 1: name
"\"AGE\" INTEGER NOT NULL ," + // 2: age
"\"NUM\" INTEGER NOT NULL);"); // 3: num
}
哎呀!發現了,INTEGER NOT NULL (integer)不能為空?這下知道原因了,int型別的是不能為空的怎麼辦呢??
我們又看到了NAME這個欄位他是TEXT型別,也就是String型別的可以為空,
因此,我們先把NUM欄位改為String型別
package cn.hnshangyu.testgreendao.bean;
import org.greenrobot.greendao.annotation.Entity;
import org.greenrobot.greendao.annotation.Id;
import org.greenrobot.greendao.annotation.Keep;
import org.greenrobot.greendao.annotation.Generated;
import org.greenrobot.greendao.annotation.NotNull;
@Entity(generateConstructors = false)
public class Student {
@Id
private Long id;
private String name;
private int age;
private String num;
public String getNum() {
return num;
}
public void setNum(String num) {
this.num = num;
}
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", age=" + age +
", num=" + num +
'}';
}
public Student() {
}
@Keep
public Student(String name, int age) {
this.name = name;
this.age = age;
}
public Student(Long id, String name, int age) {
this.id = id;
this.name = name;
this.age = age;
}
@Keep
public Long getId() {
return id;
}
@Keep
public void setId(Long id) {
this.id = id;
}
@Keep
public String getName() {
return name;
}
@Keep
public void setName(String name) {
this.name = name;
}
@Keep
public int getAge() {
return age;
}
@Keep
public void setAge(int age) {
this.age = age;
}
@Keep
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof Student)) return false;
Student student = (Student) o;
return name.equals(student.name);
}
@Keep
@Override
public int hashCode() {
return (int) (id ^ (id >>> 32));
}
}
重新進行上述資料庫更新操作,把bean物件中的num改為了String型別,
執行後結果正常,資料庫更新了!
- 看看StudentDao新建立表
/** Creates the underlying database table. */
public static void createTable(Database db, boolean ifNotExists) {
String constraint = ifNotExists? "IF NOT EXISTS ": "";
db.execSQL("CREATE TABLE " + constraint + "\"STUDENT\" (" + //
"\"_id\" INTEGER PRIMARY KEY ," + // 0: id
"\"NAME\" TEXT," + // 1: name
"\"AGE\" INTEGER NOT NULL ," + // 2: age
"\"NUM\" TEXT);"); // 3: num
}
新的欄位NUM為TEXT型別,一切正常!
總結:在greendao3.0升級資料庫時
我們基本思路為:
建立臨時表-->刪除原表-->建立新表-->複製臨時表資料到新表並刪除臨時表
並且我們新增加的和修改的欄位做好為String型別,避免欄位不能為null的情況發生
到這裡greendao3.0資料庫更新說明完畢……
有什麼不妥,歡迎指出,謝謝啦………