Realm源码分析之copyToRealm与copyToRealmOrUpdate

2023年3月7日 275次阅读来源: Android源码分析

createObject

在Realm源码分析之Writes中已经详细追踪过createObject的执行流程，此处不再赘述。
createObject有如下的两个重载方法，区别是如果Model没有指明主键使用前者，否则使用后者：
```
createObject(Class<E> clazz)

createObject(Class<E> clazz, Object primaryKeyValue)
```
注意：每次使用createObject都会创建新的Model实例。

copyToRealm与copyToRealmOrUpdate

先上Model示例代码，注意是没有指明主键的：

public class Dog extends RealmObject {
    private String name;
    private int age;

    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;
    }
}

使用copyToRealm创建model示例，如下代码：

public void copyToRealm() {
    realm.executeTransactionAsync(new Realm.Transaction() {
        @Override
        public void execute(Realm realm) {
            Dog myDog = new Dog();
            myDog.setName("Copy");
            myDog.setAge(6);
            realm.copyToRealm(myDog);
        }
    });
}

开始追踪copyToRealm，如下源码：

public <E extends RealmModel> E copyToRealm(E object) {
    checkNotNullObject(object);
    return copyOrUpdate(object, false, new HashMap<RealmModel, RealmObjectProxy>());
}

上面代码先做了对象合法性判断，然后调用了copyOrUpdate这个静态方法，如下代码：

private <E extends RealmModel> E copyOrUpdate(E object, boolean update, Map<RealmModel, RealmObjectProxy> cache) {
    checkIfValid();
    return configuration.getSchemaMediator().copyOrUpdate(this, object, update, cache);
}

在Realm源码分析之初始化中已经分析过这个Mediator实例是DefaultRealmModuleMediator，它是有注解处理器自动生成，如下代码：

public <E extends RealmModel> E copyOrUpdate(Realm realm, E obj, boolean update, Map<RealmModel, RealmObjectProxy> cache) {
    // This cast is correct because obj is either
    // generated by RealmProxy or the original type extending directly from RealmObject
    @SuppressWarnings("unchecked") Class<E> clazz = (Class<E>) ((obj instanceof RealmObjectProxy) ? obj.getClass().getSuperclass() : obj.getClass());

    if (clazz.equals(com.example.app.org.realm.demo.Dog.class)) {
        return clazz.cast(io.realm.DogRealmProxy.copyOrUpdate(realm, (com.example.app.org.realm.demo.Dog) obj, update, cache));
    }
    throw getMissingProxyClassException(clazz);
}

DefaultRealmModuleMediator只是做了中转，而是由DogRealmProxy负责实现，如下代码：

public static com.example.app.org.realm.demo.Dog copyOrUpdate(Realm realm, com.example.app.org.realm.demo.Dog object, boolean update, Map<RealmModel,RealmObjectProxy> cache) {
    if (object instanceof RealmObjectProxy && ((RealmObjectProxy) object).realmGet$proxyState().getRealm$realm() != null && ((RealmObjectProxy) object).realmGet$proxyState().getRealm$realm().threadId != realm.threadId) {
        throw new IllegalArgumentException("Objects which belong to Realm instances in other threads cannot be copied into this Realm instance.");
    }
    if (object instanceof RealmObjectProxy && ((RealmObjectProxy) object).realmGet$proxyState().getRealm$realm() != null && ((RealmObjectProxy) object).realmGet$proxyState().getRealm$realm().getPath().equals(realm.getPath())) {
        return object;
    }
    final BaseRealm.RealmObjectContext objectContext = BaseRealm.objectContext.get();
    RealmObjectProxy cachedRealmObject = cache.get(object);
    if (cachedRealmObject != null) {
        return (com.example.app.org.realm.demo.Dog) cachedRealmObject;
    }

    return copy(realm, object, update, cache);
}

上述代码，先是做了合法性判断，然后从缓存中取实例并返回，取不到就调用如下的copy方法：

public static com.example.app.org.realm.demo.Dog copy(Realm realm, com.example.app.org.realm.demo.Dog newObject, boolean update, Map<RealmModel,RealmObjectProxy> cache) {
    RealmObjectProxy cachedRealmObject = cache.get(newObject);
    if (cachedRealmObject != null) {
        return (com.example.app.org.realm.demo.Dog) cachedRealmObject;
    }

    // rejecting default values to avoid creating unexpected objects from RealmModel/RealmList fields.
    com.example.app.org.realm.demo.Dog realmObject = realm.createObjectInternal(com.example.app.org.realm.demo.Dog.class, false, Collections.<String>emptyList());
    cache.put(newObject, (RealmObjectProxy) realmObject);

    DogRealmProxyInterface realmObjectSource = (DogRealmProxyInterface) newObject;
    DogRealmProxyInterface realmObjectCopy = (DogRealmProxyInterface) realmObject;

    realmObjectCopy.realmSet$name(realmObjectSource.realmGet$name());
    realmObjectCopy.realmSet$age(realmObjectSource.realmGet$age());
    return realmObject;
}

上面方法再次取缓存并返回，取不到就调用createObjectInternal方法创建实例，并未属性赋值。而createObjectInternal已经在Realm源码分析之Writes中已经分析过了，此处不再展开了。
至此可以得出copyToRealm与createObject的区别：copyToRealm会复用Realm中缓存的Model实例。

继续使用上述的Dog，使用copyToRealmOrUpdate来创建如下代码：

public void copyToRealmOrUpdate() {
    realm.executeTransactionAsync(new Realm.Transaction() {
        @Override
        public void execute(Realm realm) {
            Dog myDog = new Dog();
            myDog.setName("Copy Update");
            myDog.setAge(6);
            realm.copyToRealmOrUpdate(myDog);
        }
    });
}

直接运行的话会crash，log如下：

Caused by: java.lang.IllegalArgumentException: A RealmObject with no @PrimaryKey cannot be updated: class com.example.app.org.realm.demo.Dog
   at io.realm.Realm.checkHasPrimaryKey(Realm.java:1615)
   at io.realm.Realm.copyToRealmOrUpdate(Realm.java:1030)
   at com.example.app.org.realm.demo.RealmActivity$5.execute(RealmActivity.java:123)
   at io.realm.Realm$1.run(Realm.java:1508)
   at io.realm.internal.async.BgPriorityRunnable.run(BgPriorityRunnable.java:34)
   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:422)
   at java.util.concurrent.FutureTask.run(FutureTask.java:237)
   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
   at java.lang.Thread.run(Thread.java:818)

上面的log很明显了，目前可以确定：copyToRealmOrUpdate方法是给指明了主键的model使用的。

让我们来揭开其神奇面纱，代码如下：

public <E extends RealmModel> E copyToRealmOrUpdate(E object) {
    checkNotNullObject(object);
    checkHasPrimaryKey(object.getClass());
    return copyOrUpdate(object, true, new HashMap<RealmModel, RealmObjectProxy>());
}

private void checkHasPrimaryKey(Class<? extends RealmModel> clazz) {
    if (!schema.getTable(clazz).hasPrimaryKey()) {
        throw new IllegalArgumentException("A RealmObject with no @PrimaryKey cannot be updated: " + clazz.toString());
    }
}

上述代码先是对象判空，然后进行主键判断，最后调用的是copyOrUpdate方法。到目前为止，copyToRealm与copyToRealmOrUpdate唯一区别是调用copyOrUpdate这个静态方法传递的第二个参数不同，如下：
```
//copyToRealm
copyOrUpdate(object, false, new HashMap<RealmModel, RealmObjectProxy>())

//copyToRealmOrUpdate
copyOrUpdate(object, true, new HashMap<RealmModel, RealmObjectProxy>())
```
紧接着回去看6中的DogRealmProxy的copyOrUpdate与copy方法，可以发现这个boolean参数实际是没有使用的。因此，可以得出：对于未指明主键的model，其copyToRealm与copyToRealmOrUpdate底层实现是一致的。

接下来修改model并指明主键，如下代码：

public class Dog extends RealmObject {
    @PrimaryKey
    private String name;
    private int age;

    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;
    }
}

发现DogRealmProxy中的copyOrUpdate方法的实现已经改变了，如下代码：

public static com.example.app.org.realm.demo.Dog copyOrUpdate(Realm realm, com.example.app.org.realm.demo.Dog object, boolean update, Map<RealmModel,RealmObjectProxy> cache) {
    if (object instanceof RealmObjectProxy && ((RealmObjectProxy) object).realmGet$proxyState().getRealm$realm() != null && ((RealmObjectProxy) object).realmGet$proxyState().getRealm$realm().threadId != realm.threadId) {
        throw new IllegalArgumentException("Objects which belong to Realm instances in other threads cannot be copied into this Realm instance.");
    }
    if (object instanceof RealmObjectProxy && ((RealmObjectProxy) object).realmGet$proxyState().getRealm$realm() != null && ((RealmObjectProxy) object).realmGet$proxyState().getRealm$realm().getPath().equals(realm.getPath())) {
        return object;
    }
    final BaseRealm.RealmObjectContext objectContext = BaseRealm.objectContext.get();
    RealmObjectProxy cachedRealmObject = cache.get(object);
    if (cachedRealmObject != null) {
        return (com.example.app.org.realm.demo.Dog) cachedRealmObject;
    }

    com.example.app.org.realm.demo.Dog realmObject = null;
    boolean canUpdate = update;
    if (canUpdate) {
        Table table = realm.getTable(com.example.app.org.realm.demo.Dog.class);
        long pkColumnIndex = table.getPrimaryKey();
        String value = ((DogRealmProxyInterface) object).realmGet$name();
        long rowIndex = Table.NO_MATCH;
        if (value == null) {
            rowIndex = table.findFirstNull(pkColumnIndex);
        } else {
            rowIndex = table.findFirstString(pkColumnIndex, value);
        }
        if (rowIndex != Table.NO_MATCH) {
            try {
                objectContext.set(realm, table.getUncheckedRow(rowIndex), realm.schema.getColumnInfo(com.example.app.org.realm.demo.Dog.class), false, Collections.<String> emptyList());
                realmObject = new io.realm.DogRealmProxy();
                cache.put(object, (RealmObjectProxy) realmObject);
            } finally {
                objectContext.clear();
            }
        } else {
            canUpdate = false;
        }
    }

    if (canUpdate) {
        return update(realm, realmObject, object, cache);
    } else {
        return copy(realm, object, update, cache);
    }
}

相比没有加主键的方法，在取不到缓存之后它增加了去Table中查询主键的过程，如果在Table找到了匹配的主键就会新建一个DogRealmProxy对象并缓存起来，最后执行update操作，其源码如下：

static com.example.app.org.realm.demo.Dog update(Realm realm, com.example.app.org.realm.demo.Dog realmObject, com.example.app.org.realm.demo.Dog newObject, Map<RealmModel, RealmObjectProxy> cache) {
    DogRealmProxyInterface realmObjectTarget = (DogRealmProxyInterface) realmObject;
    DogRealmProxyInterface realmObjectSource = (DogRealmProxyInterface) newObject;
    realmObjectTarget.realmSet$age(realmObjectSource.realmGet$age());
    return realmObject;
}

上面的update方法其实赋值操作，而copyToRealm与copyToRealmOrUpdate就到此为止了。

结论

copyToRealm与copyToRealmOrUpdate：前者是给未指明主键的model使用的，后者则是给指明主键的model使用。
copyToRealm对应无主键参数的createObject，区别是copyToRealm会复用Realm缓存的model示例，不会每次都创建新的model实例。
copyToRealmOrUpdate对应有主键参数的createObject，区别是copyToRealmOrUpdate会复用Realm缓存的model示例，没有缓存实例就要去表中查询是否有匹配这个主键存在的记录，来决定是新建对象还是更新model实例。

    原文作者：Android源码分析
    原文地址: https://blog.csdn.net/tscyds/article/details/76155031
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