GreenDAO 3.2.0：
1、在工程的build.gradle中做如下配置：
buildscript {
dependencies {
classpath 'org.greenrobot:greendao-gradle-plugin:3.0.0'
}
}
2、在app的build.gradle中做如下配置
apply plugin: 'org.greenrobot.greendao'
android {
greendao{
schemaVersion 1 // 当前数据库版本号，升级数据库则+1。
daoPackage 'com.example.greendao.gen' // 生成数据库文件的具体包
targetGenDir 'src/main/java' // 生成数据库文件的目录
}
}
dependencies {
compile 'org.greenrobot:greendao:3.2.0' // GreenDao在github上的依赖地址
}
3、创建Model类，然后，Build - Make Module 'app'
@Entity(nameInDb = "userinfo")
public class UserInfo implements Serializable {
@Id(autoincrement = true)
private Long _id;
@Property(nameInDb = "username")
private String username;
@Property(nameInDb = "age")
private int age;
......
}
4、GreenDAO的使用
ok，上面的是准备工作，接下来才是使用，即得到数据库对象进行增、删、改、查。然后根据自己的代码习惯，做封装。具体实现这里不做叙述，如果有问题欢迎留言。
推荐一篇介绍得很详细的文章，链接地址。
5、GreenDAO升级
这个也是我写这篇文章的原因，在完成上面的1-4步后，数据库增删改查都没有问题，愉快地commit and push，愉快地拿着工资吃着火锅唱着歌。
直到某一天，你在你的Model类即userinfo中加入“test”字段，你很愉快地加上了字段，在build中使greendao - schemaVersion +1，并运行......
表中没有test字段
由于你加了新的字段，表发生了变化，做数据库操作时抛出异常，找不到test字段。那么应该以怎么样的姿势新增字段和升级数据库呢？
然后各种查资料搜索，找到了以下代码，完美解决数据库升级问题。其原理也是创建临时数据库来做数据迁移。
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;
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);
}
/**
* 生成临时列表
* @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());
}
}
/**
* 存储新的数据库表 以及数据
* @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;
}
}
然后只需要继承DaoMaster.OpenHelper重写onUpgrade方法
public class SQLiteOpenHelper extends DaoMaster.OpenHelper {
public SQLiteOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
super(context, name, factory);
}
@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
MigrationHelper.getInstance().migrate(db, UserInfoDao.class);
}
}
最后在初始化DaoMaster处调用。
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