react-native之Realm資料庫的使用(一)
阿新 • • 發佈:2019-01-04
realm資料庫是一款小型資料庫系統,可以支援多個平臺,如android、ios、javascript等。當然了realm也是可以支援react-native的,官網有具體介紹,官網文件
安裝realm
npm install --save realm
然後link
react-native link realm
或者
rnpm link realm
如果link不完全,可以手動檢查新增
1.Add the following lines to android/settings.gradle:
include ':realm'
project(':realm').projectDir =new File(rootProject.projectDir,'../node_modules/realm/android')
2.Add the compile line to the dependencies in android/app/build.gradle:
dependencies {
compile project(':realm')
}
3.Add the import and link the package in MainApplication.java:
import io.realm.react.RealmReactPackage; // add this import
public class MainApplication extends Application implements ReactApplication {
@Override
protected List<ReactPackage> getPackages() {
return Arrays.<ReactPackage>asList(
new MainReactPackage(),
new RealmReactPackage() // add this line
);
}
}
React-native中用到的realm是一款物件資料庫,因此使用起來相關簡單方便;
然後關於其操作:
1. 開啟資料庫的方式,按照其介紹有兩種方式
其一、通過 open方法,eg:
// Define your models and their properties
const CarSchema = {
name: 'Car',
properties: {
make: 'string',
model: 'string',
miles: {type: 'int', default: 0},
}
};
const PersonSchema = {
name: 'Person',
properties: {
name: 'string',
birthday: 'date',
cars: 'Car[]',
picture: 'data?' // optional property
}
};
Realm.open({schema: [CarSchema, PersonSchema]})
.then(realm => {
// Create Realm objects and write to local storage
realm.write(() => {
const myCar = realm.create('Car', {
make: 'Honda',
model: 'Civic',
miles: 1000,
});
myCar.miles += 20; // Update a property value
});
// Query Realm for all cars with a high mileage
const cars = realm.objects('Car').filtered('miles > 1000');
// Will return a Results object with our 1 car
cars.length // => 1
// Add another car
realm.write(() => {
const myCar = realm.create('Car', {
make: 'Ford',
model: 'Focus',
miles: 2000,
});
});
// Query results are updated in realtime
cars.length // => 2
});
其二、通過new產生一個物件
const PersonSchema = {
name: 'Person',
properties: {
name: 'string',
testScores: 'double?[]'
}
};
let realm = new Realm({schema: [PersonSchema, CarSchema]});
realm.write(() => {
let charlie = realm.create('Person', {
name: 'Charlie',
testScores: [100.0]
});
// Charlie had an excused absense for the second test and was allowed to skip it
charlie.testScores.push(null);
// And then he didn't do so well on the third test
charlie.testScores.push(70.0);
});
- 插入資料
let realm = new Realm({schema: [PersonSchema, CarSchema]});
realm.write(() => {
let charlie = realm.create('Person', {
name: 'Charlie',
testScores: [100.0]
});
});
- 查詢資料
假設有表 Dog,下面獲取Dog表所有資料。
let dogs = realm.objects('Dog'); // retrieves all Dogs from the Realm
有時候我們需要做資料篩選,可以這樣寫
query(name){
let dogs = realm.objects('Dog');
let tanDogs = dogs.filtered('color = "tan" AND name "'+name+'"');
}
具體的篩選條件可以用到下面這些
At the moment only a subset of the NSPredicate syntax is supported in the query language. Basic comparison operators ==, !=, >, >=, <, and <= are supported for numeric properties. ==, BEGINSWITH, ENDSWITH, and CONTAINS are supported for string properties. String comparisons can be made case insensitive by appending [c] to the operator: ==[c], BEGINSWITH[c] etc. Filtering by properties on linked or child objects can by done by specifying a keypath in the query eg car.color == 'blue'
有時候我們還需要排序
let hondas = realm.objects('Car').filtered('make = "Honda"');
// Sort Hondas by mileage
let sortedHondas = hondas.sorted('miles');
// Sort in descending order instead
sortedHondas = hondas.sorted('miles', true);
// Sort by price in descending order and then miles in ascending
sortedHondas = hondas.sorted(['price', true], ['miles']);
results也可以通過儲存物件的連結物件進行排序,如:
let people = realm.objects('Person');
// Sort people by the milage of their cars
let sortedPeople = people.sorted('car.miles');
未完待續..