Android Orm框架(GreenDao)

    android项目里面很多都会有使用sqlite来保存数据。原生api真心不好使啊，要写超多超多的代码，还要写顾虑很多细节问题。于是乎就想偷懒了，干脆去网上找个orm框架吧！
    Ok，google it。筛选一下，就锁定了ormlite和greendao。简单看了一下，ormlite简单好用，比较符合JavaEE开发者使用习惯，注解真的很好用啊！再去greendao官网逛逛，他说我们的目标是：

• 最牛掰的性能
• 超好用的API
• 为Android大大优化
• 最小的内存使用
• ******

再翻翻看，还有同ormlite的性能对比：

上面可以看到，greeendao的insert和update效率要比ormlite快两倍左右，load更是夸张到4倍多。尼玛也太厉害了吧，优化这么狠。这么一大堆好处，还不赶紧使使。

    我们可以在官网上直接下来，也可去github项目主页上下载源码。建议去下载github哈，因为有源码有列子，比较直观易懂。源码使用gradle构建，需要安装gradle插件。其实真正也只有依赖一个freemaker.jar，直接网上下载一个就好。下面新建一个java工程，注意是java工程不是android工程。导入freemaker.jar和greendao-generator.jar，加入到build path。建一个如下的类：

public class DaoGenerator {

    public static void main(String[] args) throws Exception {
        // first parameter for version,  second for default generate package
        Schema schema = new Schema(1, "com.xckevin.example.model");

        addNote(schema);
        addCustomerOrder(schema);
        addUser(schema);
        // set dao class generate package
        schema.setDefaultJavaPackageDao("com.xckevin.example.dao");
        // keep custom code block
        schema.enableKeepSectionsByDefault();
        new DaoGenerator().generateAll(schema, "../GreenDaoExample/src");
    }

    private static void addNote(Schema schema) {
        Entity note = schema.addEntity("Note");
        note.addIdProperty();
        note.addStringProperty("text").notNull();
        note.addStringProperty("comment");
        note.addDateProperty("date");
    }
    
    private static void addUser(Schema schema) {
    	Entity user = schema.addEntity("User");
    	user.setTableName("t_user");
    	user.addIdProperty();
    	user.addStringProperty("account").unique();
    	user.addStringProperty("password");
    	user.addDateProperty("birthday");
    	user.addShortProperty("gender");
    	user.addIntProperty("height");
    	user.addFloatProperty("weight");
    	user.addDateProperty("registerTime");
    	user.implementsInterface("Jsonable<User>");
    }

    private static void addCustomerOrder(Schema schema) {
        Entity customer = schema.addEntity("Customer");
        customer.addIdProperty();
        customer.addStringProperty("name").notNull();

        Entity order = schema.addEntity("Order");
        order.setTableName("ORDERS"); // "ORDER" is a reserved keyword
        order.addIdProperty();
        Property orderDate = order.addDateProperty("date").getProperty();
        Property customerId = order.addLongProperty("customerId").notNull().getProperty();
        order.addToOne(customer, customerId);

        ToMany customerToOrders = customer.addToMany(order, customerId);
        customerToOrders.setName("orders");
        customerToOrders.orderAsc(orderDate);
    }

}

代码号简单的话，看名字就知道是什么意思了。greendao支持各种类型的哇，还支持一对一、一对多、多对多的关系，很强悍！直接运行，代码生成

自动生成model和dao，倍儿爽！随便看一个model类：

package com.xckevin.example.model;

// THIS CODE IS GENERATED BY greenDAO, EDIT ONLY INSIDE THE "KEEP"-SECTIONS

// KEEP INCLUDES - put your custom includes here
import org.json.JSONException;
import org.json.JSONObject;
// KEEP INCLUDES END
/**
 * Entity mapped to table t_user.
 */
public class User implements Jsonable<User> {

    private Long id;
    private String account;
    private String password;
    private java.util.Date birthday;
    private Short gender;
    private Integer height;
    private Float weight;
    private java.util.Date registerTime;

    // KEEP FIELDS - put your custom fields here
    // KEEP FIELDS END

    public User() {
    }

    public User(Long id) {
        this.id = id;
    }

    public User(Long id, String account, String password, java.util.Date birthday, Short gender, Integer height, Float weight, java.util.Date registerTime) {
        this.id = id;
        this.account = account;
        this.password = password;
        this.birthday = birthday;
        this.gender = gender;
        this.height = height;
        this.weight = weight;
        this.registerTime = registerTime;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getAccount() {
        return account;
    }

    public void setAccount(String account) {
        this.account = account;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public java.util.Date getBirthday() {
        return birthday;
    }

    public void setBirthday(java.util.Date birthday) {
        this.birthday = birthday;
    }

    public Short getGender() {
        return gender;
    }

    public void setGender(Short gender) {
        this.gender = gender;
    }

    public Integer getHeight() {
        return height;
    }

    public void setHeight(Integer height) {
        this.height = height;
    }

    public Float getWeight() {
        return weight;
    }

    public void setWeight(Float weight) {
        this.weight = weight;
    }

    public java.util.Date getRegisterTime() {
        return registerTime;
    }

    public void setRegisterTime(java.util.Date registerTime) {
        this.registerTime = registerTime;
    }

    // KEEP METHODS - put your custom methods here
    @Override
	public User parse(JSONObject jsonObj) {
		// TODO Auto-generated method stub
    	try {
			id = jsonObj.getLong("id");
			account = jsonObj.getString("account");
			return this;
		} catch (JSONException e) {
			e.printStackTrace();
		}
		return null;
	}
    // KEEP METHODS END

}

注意上面的// KEEP代码块中是手动加入了，当设置了

schema.enableKeepSectionsByDefault

后，该部分代码块在下次更新的时候会保留下来。

dao类中也有各种基本的方法，如insert,update,delete等等。基本可能完成大部分需求了，终于不用写那么繁琐的数据库操作啦！

    再看看怎么在client获取到dao，注意client要加入greendao.jar哦。有了dao就可以对数据库各种操作了！

        DevOpenHelper helper = new DaoMaster.DevOpenHelper(this, "notes-db", null);
        db = helper.getWritableDatabase();
        daoMaster = new DaoMaster(db);
        daoSession = daoMaster.newSession();
        userDao = daoSession.getUserDao();

总体来说，ormlite使用简单，学习成本低，容易上手，效率比greendao偏慢一点。greendao耦合性高，使用时要另外使用一个java工程创建，开始环境搭建比较麻烦，但是一旦上手还是十分容易使用的，并且效率最好。个人还是推荐使用greendao。