前言
在android开发中，可供选择的数据库很多，如 greenDAO，Realm，ormlite-android等很多，其中本人用过的有greenDAO，Realm，在上一篇中介绍了greenDAO 3.2的简单使用,在本文将简单地介绍一下realm
配置环境
1. 在（project）项目的 build.gradle 文件中添加如下配置
buildscript {
repositories {
jcenter()
}
dependencies {
classpath "io.realm:realm-gradle-plugin:3.0.0"
}
}
2. 在module中的 build.gradle 文件中添加如下配置
apply plugin: 'realm-android'
使用方法
1. 初始化数据库，一般在Application中初始化
/**
* Realm对象只能在创建它的线程中使用
*/
private void initRealm() {
Realm.init(this);
RealmConfiguration realmConfiguration = new RealmConfiguration.Builder()
.schemaVersion(3)//数据库版本
.name("Note.realm")//数据库名称
// .migration(migration) 数据库升迁
.build();
Realm.setDefaultConfiguration(realmConfiguration);
}
2. 创建对象，并继承RealmObject
User类
public class User extends RealmObject {
@PrimaryKey
private long id;
@Required //强制不为null,默认为""
private String name;
//@Ignore
private int age;
//@Ignore
private boolean sex;
@Ignore //不被保存
private int sessionId;
//@Ignore
private RealmList emails;//一对多
public User(long id, String name, int age) {
this.id = id;
this.name = name;
this.age = age;
}
public User(String name, int age) {
this.name = name;
this.age = age;
}
public boolean isSex() {
return sex;
}
public void setSex(boolean sex) {
this.sex = sex;
}
public RealmList getEmails() {
return emails;
}
public void setEmails(RealmList emails) {
this.emails = emails;
}
//必须要有默认构造函数
public User() {
}
public void setId(long id) {
this.id = id;
}
public long getId() {
return id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public int getSessionId() {
return sessionId;
}
public void setSessionId(int sessionId) {
this.sessionId = sessionId;
}
}
Email类
public class Email extends RealmObject {
private String address;
private boolean active;
// @Ignore
private String type;
public Email(String address, boolean active) {
this.address = address;
this.active = active;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public boolean isActive() {
return active;
}
public void setActive(boolean active) {
this.active = active;
}
public Email() {
}
}
3. 增删改查
realm = Realm.getDefaultInstance();//获取realm对象
增
private void insert() {
//方法一
// realm.beginTransaction();
// User user = realm.createObject(User.class,1); // Create a new object
// user.setName("yuShu");
// user.setAge(18);
// realm.commitTransaction();
// //方法二,创建一个非管托的对象，通过realm.copyToRealm(user2)
// User user2 = new User(1,"yuShu", 18);
// realm.beginTransaction();
// realm.copyToRealmOrUpdate(user2);//对象存在则更新，否则插入
// realm.commitTransaction();
//方法三：自动处理写入事物的开始和提交，并在错误发生时取消写入事物
realm.executeTransaction(new Realm.Transaction() {
@Override
public void execute(Realm realm) {
RealmList emails = new RealmList<>();
for (int i = 0; i < 3; i++) {
Email email = realm.createObject(Email.class);
email.setActive(false);
email.setAddress(i + "[email protected]");
email.setType("QQ");
emails.add(email);
}
User user = realm.createObject(User.class, 1);//id不可重复
user.setName("yuShu");
user.setAge(28);
user.setSex(true);
user.setSessionId(111);
user.setEmails(emails);//设置一对多关系
Log.i(TAG, "execute: ");
}
});
}
删
private void delete() {
final RealmResults results = realm.where(User.class).findAll();
// All changes to data must happen in a transaction
realm.executeTransaction(new Realm.Transaction() {
@Override
public void execute(Realm realm) {
// remove single match
// results.deleteFirstFromRealm(); //删除第一个
// results.deleteLastFromRealm(); //删除最后一个
// remove a single object
User user = results.get(1);
user.deleteFromRealm();
// // Delete all matches
// results.deleteAllFromRealm(); //删除所有
}
});
}
改
private User findByEmail() {
RealmQuery query = realm.where(User.class);
return query.equalTo("emails.address", "[email protected]").findFirst();//emails必须是字段
}
private void update() {
User user = findByEmail();
realm.beginTransaction();
user.setAge(25);
user.setName("GuYuShu");
realm.commitTransaction();
}
查
private User findByEmail() {
RealmQuery query = realm.where(User.class);
return query.equalTo("emails.address", "[email protected]").findFirst();//emails必须是字段
}
private User findById(long id) {
RealmQuery query = realm.where(User.class);
// 组合查询
query.equalTo("id", id)
.beginGroup()
.equalTo("name", "yuShu")
.or()
.contains("name", "Jo")
.endGroup();
User user = query.findFirst();
return user;
}
private RealmResults findAll() {
RealmQuery query = realm.where(User.class);
return query.findAll();
}
4. 数据库升迁
/**
* Realm对象只能在创建它的线程中使用
*/
private void initRealm() {
Realm.init(this);
realmConfiguration = new RealmConfiguration.Builder()
.schemaVersion(3)//数据库版本
.name("Note.realm")//数据库名称
.migration(migration)//数据库升迁
.build();
Realm.setDefaultConfiguration(realmConfiguration);
}
//升级
RealmMigration migration = new RealmMigration() {
@Override
public void migrate(DynamicRealm realm, long oldVersion, long newVersion) {
RealmSchema schema = realm.getSchema();
if (oldVersion == 0) {
schema.get("User")
.addField("age", int.class)
.addRealmListField("emails", schema.get("Email"));
oldVersion++;
}
if (oldVersion == 1) {
schema.get("User")
.addField("sex", boolean.class);
oldVersion++;
}
if (oldVersion == 2) {
schema.get("Email")
.addField("type", String.class);
}
}
};
以上只是介绍了realm的基本使用，更详细的资料可以查看官网