安卓数据库之 Realm for Androd
来源:互联网 发布:java集合类特点 编辑:程序博客网 时间:2024/06/05 22:36
目录
1、Realm简介
2、环境配置
3、在Application中初始化Realm
4、创建实体
5、增删改查
6、异步操作
7、数据迁移(版本升级)
Demo地址(https://github.com/RaphetS/DemoRealm )
Demo地址:https://github.com/RaphetS/DemoRealm
一、Realm简介
数据库Realm,是用来替代sqlite的一种解决方案,它有一套自己的数据库存储引擎,比sqlite更轻量级,拥有更快的速度,并且具有很多现代数据库的特性,比如支持JSON,流式api,数据变更通知,自动数据同步,简单身份验证,访问控制,事件处理,最重要的是跨平台,目前已有Java,Objective C,Swift,React-Native,Xamarin这五种实现。
本篇文章用的版本为Realm 2.0.2(官方文档)
二、环境配置
(1) 在项目的build文件加上
buildscript { repositories { jcenter() } dependencies { classpath "io.realm:realm-gradle-plugin:2.0.2" }}
(2) 在app的build文件加上
apply plugin: 'realm-android'
三、初始化Realm
(1) 在Application的oncreate()方法中Realm.init()
public class MyApplication extends Application { @Override public void onCreate() { super.onCreate(); Realm.init(this); }}
(2)在Application的oncreate()方法中对Realm进行相关配置
①使用默认配置
public class MyApplication extends Application { @Override public void onCreate() { super.onCreate(); // The Realm file will be located in Context.getFilesDir() with name "default.realm" Realm.init(this); RealmConfiguration config = new RealmConfiguration.Builder().build(); Realm.setDefaultConfiguration(config); }}
②使用自定义配置
public class MyApplication extends Application { @Override public void onCreate() { super.onCreate(); Realm.init(this); RealmConfiguration config = new RealmConfiguration.Builder() .name("myRealm.realm") .deleteRealmIfMigrationNeeded() .build(); Realm.setDefaultConfiguration(config); }}
(3)在AndroidManifest.xml配置自定义的Application
<application android:name=".MyApplication" .../>
四、创建实体
(1)新建一个类继承RealmObject
public class Dog extends RealmObject { private String name; private int age; @PrimaryKey private String 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 String getId() { return id; } public void setId(String id) { this.id = id; }}
多对多的关系:
public class Contact extends RealmObject { public String name; public RealmList<Email> emails;}public class Email extends RealmObject { public String address; public boolean active;}
(2)其他相关说明
1、支持的数据类型:
boolean, byte, short, int, long, float, double, String, Date and byte[]
在Realm中byte, short, int, long最终都被映射成long类型
2、注解说明
@PrimaryKey
①字段必须是String、 integer、byte、short、 int、long 以及它们的封装类Byte, Short, Integer, and Long
②使用了该注解之后可以使用copyToRealmOrUpdate()方法,通过主键查询它的对象,如果查询到了,则更新它,否则新建一个对象来代替。
③使用了该注解将默认设置@index注解
④使用了该注解之后,创建和更新数据将会慢一点,查询数据会快一点。
@Required
数据不能为null
@Ignore
忽略,即该字段不被存储到本地
@Index
为这个字段添加一个搜索引擎,这将使插入数据变慢、数据增大,但是查询会变快。建议在需要优化读取性能的情况下使用。
五、增
(1)实现方法一:事务操作
类型一 :新建一个对象,并进行存储
Realm realm=Realm.getDefaultInstance();realm.beginTransaction();User user = realm.createObject(User.class); // Create a new objectuser.setName("John");user.setEmail("john@corporation.com");realm.commitTransaction();
类型二:复制一个对象到Realm数据库
Realm realm=Realm.getDefaultInstance();User user = new User("John");user.setEmail("john@corporation.com");// Copy the object to Realm. Any further changes must happen on realmUserrealm.beginTransaction();realm.copyToRealm(user);realm.commitTransaction();
(2)实现方法二:使用事务块
Realm mRealm=Realm.getDefaultInstance();final User user = new User("John");user.setEmail("john@corporation.com");mRealm.executeTransaction(new Realm.Transaction() { @Override public void execute(Realm realm) { realm.copyToRealm(user); } });
六、删
Realm mRealm=Realm.getDefaultInstance(); final RealmResults<Dog> dogs= mRealm.where(Dog.class).findAll(); mRealm.executeTransaction(new Realm.Transaction() { @Override public void execute(Realm realm) { Dog dog=dogs.get(5); dog.deleteFromRealm(); //删除第一个数据 dogs.deleteFirstFromRealm(); //删除最后一个数据 dogs.deleteLastFromRealm(); //删除位置为1的数据 dogs.deleteFromRealm(1); //删除所有数据 dogs.deleteAllFromRealm(); } });
同样也可以使用同上的beginTransaction和commitTransaction方法进行删除
七、改
Realm mRealm=Realm.getDefaultInstance();Dog dog = mRealm.where(Dog.class).equalTo("id", id).findFirst();mRealm.beginTransaction();dog.setName(newName);mRealm.commitTransaction();
同样也可以用事物块来更新数据
八、查
(1)查询全部
查询结果为RealmResults<T>,可以使用mRealm.copyFromRealm(dogs)方法将它转为List<T>
public List<Dog> queryAllDog() { Realm mRealm=Realm.getDefaultInstance(); RealmResults<Dog> dogs = mRealm.where(Dog.class).findAll(); return mRealm.copyFromRealm(dogs); }
(2)条件查询
public Dog queryDogById(String id) { Realm mRealm=Realm.getDefaultInstance(); Dog dog = mRealm.where(Dog.class).equalTo("id", id).findFirst(); return dog; }
常见的条件如下(详细资料请查官方文档):
between(), greaterThan(), lessThan(), greaterThanOrEqualTo() & lessThanOrEqualTo()
equalTo() & notEqualTo()
contains(), beginsWith() & endsWith()
isNull() & isNotNull()
isEmpty() & isNotEmpty()
(3)对查询结果进行排序
/** * query (查询所有) */ public List<Dog> queryAllDog() { RealmResults<Dog> dogs = mRealm.where(Dog.class).findAll(); /** * 对查询结果,按Id进行排序,只能对查询结果进行排序 */ //增序排列 dogs=dogs.sort("id"); //降序排列 dogs=dogs.sort("id", Sort.DESCENDING); return mRealm.copyFromRealm(dogs); }
(4)其他查询
sum,min,max,average只支持整型数据字段
/** * 查询平均年龄 */ private void getAverageAge() { double avgAge= mRealm.where(Dog.class).findAll().average("age"); } /** * 查询总年龄 */ private void getSumAge() { Number sum= mRealm.where(Dog.class).findAll().sum("age"); int sumAge=sum.intValue(); } /** * 查询最大年龄 */ private void getMaxId(){ Number max= mRealm.where(Dog.class).findAll().max("age"); int maxAge=max.intValue(); }
九、异步操作
大多数情况下,Realm的增删改查操作足够快,可以在UI线程中执行操作。但是如果遇到较复杂的增删改查,或增删改查操作的数据较多时,就可以子线程进行操作。
(1)异步增:
private void addCat(final Cat cat) { RealmAsyncTask addTask= mRealm.executeTransactionAsync(new Realm.Transaction() { @Override public void execute(Realm realm) { realm.copyToRealm(cat); } }, new Realm.Transaction.OnSuccess() { @Override public void onSuccess() { ToastUtil.showShortToast(mContext,"收藏成功"); } }, new Realm.Transaction.OnError() { @Override public void onError(Throwable error) { ToastUtil.showShortToast(mContext,"收藏失败"); } }); }
最后在销毁Activity或Fragment时,要取消掉异步任务
@Override protected void onDestroy() { super.onDestroy(); if (addTask!=null&&!addTask.isCancelled()){ addTask.cancel(); } }
(2)异步删
private void deleteCat(final String id, final ImageView imageView){ RealmAsyncTask deleteTask= mRealm.executeTransactionAsync(new Realm.Transaction() { @Override public void execute(Realm realm) { Cat cat=realm.where(Cat.class).equalTo("id",id).findFirst(); cat.deleteFromRealm(); } }, new Realm.Transaction.OnSuccess() { @Override public void onSuccess() { ToastUtil.showShortToast(mContext,"取消收藏成功"); } }, new Realm.Transaction.OnError() { @Override public void onError(Throwable error) { ToastUtil.showShortToast(mContext,"取消收藏失败"); } }); }
最后在销毁Activity或Fragment时,要取消掉异步任务
@Override protected void onDestroy() { super.onDestroy(); if (deleteTask!=null&&!addTask.isCancelled()){ deleteTask.cancel(); } }
(3)异步改
RealmAsyncTask updateTask= mRealm.executeTransactionAsync(new Realm.Transaction() { @Override public void execute(Realm realm) { Cat cat=realm.where(Cat.class).equalTo("id",mId).findFirst(); cat.setName(name); } }, new Realm.Transaction.OnSuccess() { @Override public void onSuccess() { ToastUtil.showShortToast(UpdateCatActivity.this,"更新成功"); } }, new Realm.Transaction.OnError() { @Override public void onError(Throwable error) { ToastUtil.showShortToast(UpdateCatActivity.this,"失败成功"); } });
最后在销毁Activity或Fragment时,要取消掉异步任务
@Override protected void onDestroy() { super.onDestroy(); if (updateTask!=null&&!addTask.isCancelled()){ updateTask.cancel(); } }
(4)异步查
RealmResults<Cat> cats=mRealm.where(Cat.class).findAllAsync(); cats.addChangeListener(new RealmChangeListener<RealmResults<Cat>>() { @Override public void onChange(RealmResults<Cat> element) { element= element.sort("id"); List<Cat> datas=mRealm.copyFromRealm(element); } });
最后在销毁Activity或Fragment时,要取消掉异步任务
@Override protected void onDestroy() { super.onDestroy(); cats.removeChangeListeners(); }
十、数据迁移(版本升级)
方法一、删除旧版本的数据
RealmConfiguration config = new RealmConfiguration.Builder() .deleteRealmIfMigrationNeeded() .build()
方法二、设置schema 版本和 migration,对改变的数据进行处理
RealmConfiguration config = new RealmConfiguration.Builder() .schemaVersion(2) // Must be bumped when the schema changes .migration(new Migration()) // Migration to run instead of throwing an exception .build()
处理版本数据变化Migration
public class Migration implements RealmMigration { @Override public void migrate(final DynamicRealm realm, long oldVersion, long newVersion) { // During a migration, a DynamicRealm is exposed. A DynamicRealm is an untyped variant of a normal Realm, but // with the same object creation and query capabilities. // A DynamicRealm uses Strings instead of Class references because the Classes might not even exist or have been // renamed. // Access the Realm schema in order to create, modify or delete classes and their fields. RealmSchema schema = realm.getSchema(); /************************************************ // Version 0 class Person @Required String firstName; @Required String lastName; int age; // Version 1 class Person @Required String fullName; // combine firstName and lastName into single field. int age; ************************************************/ // Migrate from version 0 to version 1 if (oldVersion == 0) { RealmObjectSchema personSchema = schema.get("Person"); // Combine 'firstName' and 'lastName' in a new field called 'fullName' personSchema .addField("fullName", String.class, FieldAttribute.REQUIRED) .transform(new RealmObjectSchema.Function() { @Override public void apply(DynamicRealmObject obj) { obj.set("fullName", obj.getString("firstName") + " " + obj.getString("lastName")); } }) .removeField("firstName") .removeField("lastName"); oldVersion++; } /************************************************ // Version 2 class Pet // add a new model class @Required String name; @Required String type; class Person @Required String fullName; int age; RealmList<Pet> pets; // add an array property ************************************************/ // Migrate from version 1 to version 2 if (oldVersion == 1) { // Create a new class RealmObjectSchema petSchema = schema.create("Pet") .addField("name", String.class, FieldAttribute.REQUIRED) .addField("type", String.class, FieldAttribute.REQUIRED); // Add a new field to an old class and populate it with initial data schema.get("Person") .addRealmListField("pets", petSchema) .transform(new RealmObjectSchema.Function() { @Override public void apply(DynamicRealmObject obj) { if (obj.getString("fullName").equals("JP McDonald")) { DynamicRealmObject pet = realm.createObject("Pet"); pet.setString("name", "Jimbo"); pet.setString("type", "dog"); obj.getList("pets").add(pet); } } }); oldVersion++; } /************************************************ // Version 3 class Pet @Required String name; int type; // type becomes int class Person String fullName; // fullName is nullable now RealmList<Pet> pets; // age and pets re-ordered (no action needed) int age; ************************************************/ // Migrate from version 2 to version 3 if (oldVersion == 2) { RealmObjectSchema personSchema = schema.get("Person"); personSchema.setNullable("fullName", true); // fullName is nullable now. // Change type from String to int schema.get("Pet") .addField("type_tmp", int.class) .transform(new RealmObjectSchema.Function() { @Override public void apply(DynamicRealmObject obj) { String oldType = obj.getString("type"); if (oldType.equals("dog")) { obj.setLong("type_tmp", 1); } else if (oldType.equals("cat")) { obj.setInt("type_tmp", 2); } else if (oldType.equals("hamster")) { obj.setInt("type_tmp", 3); } } }) .removeField("type") .renameField("type_tmp", "type"); oldVersion++; } }}
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