目錄
1、Realm簡介
2、環境配置
3、在Application中初始化Realm
4、創建實體
5、增刪改查
6、異步操作
7、數據遷移(版本升級)
Demo地址(https://github.com/RaphetS/DemoRealm )
Demo地址:https://github.com/RaphetS/DemoRealm
一、Realm簡介
數據庫Realm,是用來替代sqlite的一種解決方案,它有一套自己的數據庫存儲引擎,比sqlite更輕量級,擁有更快的速度,並且具有很多現代數據庫的特性,比如支持JSON,流式api,數據變更通知,自動數據同步,簡單身份驗證,訪問控制,事件處理,最重要的是跨平臺,目前已有Java,Objective C,Swift,React-Native,Xamarin這五種實現。
本篇文章用的版本爲Realm 2.0.2(官方文檔)
二、環境配置
(1) 在項目的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()方法中對Realm進行相關配置
①使用默認配置
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使用自定義配置
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配置自定義的Application
<application
android:name=".MyApplication"
...
/>
四、創建實體
(1)新建一個類繼承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;
}
}
多對多的關係:
public class Contact extends RealmObject {
public String name;
public RealmList<Email> emails;
}
public class Email extends RealmObject {
public String address;
public boolean active;
}
(2)其他相關說明
1、支持的數據類型:
boolean, byte, short, int, long, float, double, String, Date and byte[]
在Realm中byte, short, int, long最終都被映射成long類型
2、註解說明
@PrimaryKey
①字段必須是String、 integer、byte、short、 int、long 以及它們的封裝類Byte, Short, Integer, and Long
②使用了該註解之後可以使用copyToRealmOrUpdate()方法,通過主鍵查詢它的對象,如果查詢到了,則更新它,否則新建一個對象來代替。
③使用了該註解將默認設置@index註解
④使用了該註解之後,創建和更新數據將會慢一點,查詢數據會快一點。
@Required
數據不能爲null
@Ignore
忽略,即該字段不被存儲到本地
@Index
爲這個字段添加一個搜索引擎,這將使插入數據變慢、數據增大,但是查詢會變快。建議在需要優化讀取性能的情況下使用。
五、增
(1)實現方法一:事務操作
類型一 :新建一個對象,並進行存儲
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();
類型二:複製一個對象到Realm數據庫
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)實現方法二:使用事務塊
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、刪
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();
//刪除第一個數據
dogs.deleteFirstFromRealm();
//刪除最後一個數據
dogs.deleteLastFromRealm();
//刪除位置爲1的數據
dogs.deleteFromRealm(1);
//刪除所有數據
dogs.deleteAllFromRealm();
}
});
同樣也可以使用同上的beginTransaction和commitTransaction方法進行刪除
七、改
Realm mRealm=Realm.getDefaultInstance();
Dog dog = mRealm.where(Dog.class).equalTo("id", id).findFirst();
mRealm.beginTransaction();
dog.setName(newName);
mRealm.commitTransaction();
同樣也可以用事物塊來更新數據
八、查
(1)查詢全部
查詢結果爲RealmResults<T>,可以使用mRealm.copyFromRealm(dogs)方法將它轉爲List<T>
public List<Dog> queryAllDog() {
Realm mRealm=Realm.getDefaultInstance();
RealmResults<Dog> dogs = mRealm.where(Dog.class).findAll();
return mRealm.copyFromRealm(dogs);
}
(2)條件查詢
public Dog queryDogById(String id) {
Realm mRealm=Realm.getDefaultInstance();
Dog dog = mRealm.where(Dog.class).equalTo("id", id).findFirst();
return dog;
}
常見的條件如下(詳細資料請查官方文檔):
-
between(), greaterThan(), lessThan(), greaterThanOrEqualTo() & lessThanOrEqualTo()
-
equalTo() & notEqualTo()
-
contains(), beginsWith() & endsWith()
-
isNull() & isNotNull()
-
isEmpty() & isNotEmpty()
(3)對查詢結果進行排序
/**
* query (查詢所有)
*/
public List<Dog> queryAllDog() {
RealmResults<Dog> dogs = mRealm.where(Dog.class).findAll();
/**
* 對查詢結果,按Id進行排序,只能對查詢結果進行排序
*/
//增序排列
dogs=dogs.sort("id");
//降序排列
dogs=dogs.sort("id", Sort.DESCENDING);
return mRealm.copyFromRealm(dogs);
}
(4)其他查詢
sum,min,max,average只支持整型數據字段
/**
* 查詢平均年齡
*/
private void getAverageAge() {
double avgAge= mRealm.where(Dog.class).findAll().average("age");
}
/**
* 查詢總年齡
*/
private void getSumAge() {
Number sum= mRealm.where(Dog.class).findAll().sum("age");
int sumAge=sum.intValue();
}
/**
* 查詢最大年齡
*/
private void getMaxId(){
Number max= mRealm.where(Dog.class).findAll().max("age");
int maxAge=max.intValue();
}
九、異步操作
大多數情況下,Realm的增刪改查操作足夠快,可以在UI線程中執行操作。但是如果遇到較複雜的增刪改查,或增刪改查操作的數據較多時,就可以子線程進行操作。
(1)異步增:
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,"收藏失敗");
}
});
}
最後在銷燬Activity或Fragment時,要取消掉異步任務
@Override
protected void onDestroy() {
super.onDestroy();
if (addTask!=null&&!addTask.isCancelled()){
addTask.cancel();
}
}
(2)異步刪
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,"取消收藏失敗");
}
});
}
最後在銷燬Activity或Fragment時,要取消掉異步任務
@Override
protected void onDestroy() {
super.onDestroy();
if (deleteTask!=null&&!addTask.isCancelled()){
deleteTask.cancel();
}
}
(3)異步改
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,"失敗成功");
}
});
最後在銷燬Activity或Fragment時,要取消掉異步任務
@Override
protected void onDestroy() {
super.onDestroy();
if (updateTask!=null&&!addTask.isCancelled()){
updateTask.cancel();
}
}
(4)異步查
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);
}
});
最後在銷燬Activity或Fragment時,要取消掉異步任務
@Override
protected void onDestroy() {
super.onDestroy();
cats.removeChangeListeners();
}
十、數據遷移(版本升級)
方法一、刪除舊版本的數據
RealmConfiguration config = new RealmConfiguration.Builder()
.deleteRealmIfMigrationNeeded()
.build()
方法二、設置schema 版本和 migration,對改變的數據進行處理
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()
處理版本數據變化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++;
}
}
}