Realm数据库迁移实例

RealmMigrationDemo.java

package com.brucetoo.realmdemo.realmmigration;

import android.app.Application;
import android.util.Log;

import io.realm.Realm;
import io.realm.RealmConfiguration;
import io.realm.RealmMigration;
import io.realm.RealmObject;
import io.realm.internal.ColumnType;
import io.realm.internal.Table;

/**
 * Created by Bruce Too
 * On 8/19/15.
 * At 10:47
 * Realm数据库迁移实例
 */
public class RealmMigrationDemo extends Application{


    @Override
    public void onCreate() {
        super.onCreate();
        //首先在初次数据库配置中声明 version，当然这个操作通常是在Application中完成
        RealmConfiguration config = new RealmConfiguration.Builder(this)
                .name("database")
                .schemaVersion(0)  //初始化版本的version = 0
                .build();

        //然后设置对person设置值
        Realm realm = Realm.getInstance(config);

        realm.beginTransaction();
        Person person = realm.createObject(Person.class);
        person.setFullName("fullname");
        person.setAge(15);
        realm.commitTransaction(); //提交事务后数据库就存在了保存的值

        //假设现在数据库中Person字段需要添加一个参数 time,就需要做数据库的迁移操作了
        /**
         * 1.需要将默认配置中的schemaVersion在原来的基础上+1，在此是 0+1=1
         * 2.配置迁移的Migration
         */
    }

    //假设在第一次Person的中的参数如下：
    public class Person extends RealmObject {

        private String fullName;
        private int age;

        private long time; //第二个版本添加的字段

        public long getTime() {
            return time;
        }

        public void setTime(long time) {
            this.time = time;
        }

        public String getFullName() {
            return fullName;
        }

        public void setFullName(String fullName) {
            this.fullName = fullName;
        }

        public int getAge() {
            return age;
        }

        public void setAge(int age) {
            this.age = age;
        }
    }


    public class Migration implements RealmMigration {


        @Override
        public long execute(Realm realm, long version) {
            Log.e("version:",String.valueOf(version));

            //从版本 0 升级到 1
            /*
             version 0
             Person
                private String fullName;
                private int age;

             version 1
                 private String fullName;
                 private int age;
                 private long time;

             */
            if(version == 0){
                //获取person类保存的table
               Table personTable = realm.getTable(Person.class);
                //添加一个字段 time
                long timeIndex = personTable.addColumn(ColumnType.INTEGER,"time");
                for(int i = 0; i < personTable.size(); i++){
                    //为每个time字段赋值
                    personTable.setString(timeIndex,i,"11111");
                }

                //版本号加1
                version++;
            }

 /*********************如果还有版本迭代了很多次,则需要依次对每个版本的迁移做操作*******************************************/
          /*
            // Version 2
                class Pet                   // add a new model class
                    String name;
                    String type;

                class Person
                    String fullName;
                    int age;
                    RealmList<Pet> pets;    // add an array property

        */
            // Migrate from version 1 to version 2
            if (version == 1) {
//            Table personTable = realm.getTable(Person.class);
//            Table petTable = realm.getTable(Pet.class);
//            petTable.addColumn(ColumnType.STRING, "name");
//            petTable.addColumn(ColumnType.STRING, "type");
//            long petsIndex = personTable.addColumnLink(ColumnType.LINK_LIST, "pets", petTable);
//            long fullNameIndex = getIndexForProperty(personTable, "fullName");
//
//            for (int i = 0; i < personTable.size(); i++) {
//                if (personTable.getString(fullNameIndex, i).equals("JP McDonald")) {
//                    personTable.getUncheckedRow(i).getLinkList(petsIndex).add(petTable.add("Jimbo", "dog"));
//                }
//            }
//            version++;
            }

        /*
            // Version 3
                class Pet
                    String name;
                    int type;               // type becomes int

                class Person
                    String fullName;
                    RealmList<Pet> pets;    // age and pets re-ordered
                    int age;
        */
            // Migrate from version 2 to version 3
//        if (version == 2) {
//            Table petTable = realm.getTable(Pet.class);
//            long oldTypeIndex = getIndexForProperty(petTable, "type");
//            long typeIndex = petTable.addColumn(ColumnType.INTEGER, "type");
//            for (int i = 0; i < petTable.size(); i++) {
//                String type = petTable.getString(oldTypeIndex, i);
//                if (type.equals("dog")) {
//                    petTable.setLong(typeIndex, i, 1);
//                }
//                else if (type.equals("cat")) {
//                    petTable.setLong(typeIndex, i, 2);
//                }
//                else if (type.equals("hamster")) {
//                    petTable.setLong(typeIndex, i, 3);
//                }
//            }
//            petTable.removeColumn(oldTypeIndex);
//            version++;
//        }


//        if(version == 3){
//            Table personTable = realm.getTable(Person.class);
//            long timeIndex = personTable.addColumn(ColumnType.STRING,"time");
//            Log.e("version:",version+"");
//            for(int i = 0; i < personTable.size(); i++){
//                personTable.setString(timeIndex,i,"11111111");
//            }
////            version++;
//        }


            return version;
        }

        private long getIndexForProperty(Table table, String name) {
            for (int i = 0; i < table.getColumnCount(); i++) {
                if (table.getColumnName(i).equals(name)) {
                    return i;
                }
            }
            return -1;
        }
    }

}