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
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 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 object
user.setName("John");
user.setEmail("[email protected]");
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("[email protected]");
// Copy the object to Realm. Any further changes must happen on realmUser
realm.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("[email protected]");
mRealm.executeTransaction(new Realm.Transaction() {
@Override
public void execute(Realm realm) {
realm.copyToRealm(user);
}
});
六、删
Realm mRealm=Realm.getDefaultInstance();
final RealmResults 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
public List queryAllDog() {
Realm mRealm=Realm.getDefaultInstance();
RealmResults 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 queryAllDog() {
RealmResults 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 cats=mRealm.where(Cat.class).findAllAsync();
cats.addChangeListener(new RealmChangeListener>() {
@Override
public void onChange(RealmResults element) {
element= element.sort("id");
List 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 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 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++;
}
}
}
十一、最后
花了将近一周的时间写了这篇文章以及Demo,希望对大家有所帮助。有什么问题欢迎大家提出,共同学习,一起进步。
Demo是以本地收藏为应用场景的,实现了对Realm的增删改查等操作,以及异步的增删改查操作,过程中也踩了不少的坑。
Demo体验:
Demo地址:https://github.com/RaphetS/DemoRealm
欢迎大家Star、Fork。