CRUD - 更新 - Java SDK

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关于本页中的示例

修改对象
更新或插入（upsert）对象
更新collection
迭代

Atlas Device SDK 已弃用。有关详细信息，请参阅弃用页面。

关于本页中的示例

本页上的示例使用具有两种 Realm 对象类型的项目管理应用的Realm 数据模型： Project和Task 。 Project具有零个或多个Tasks 。

请参阅 Project 和 Task 这两个类的模式，如下所示：

ProjectTask.java

import org.bson.types.ObjectId;
import io.realm.RealmObject;
import io.realm.annotations.PrimaryKey;
import io.realm.annotations.RealmClass;
import io.realm.annotations.Required;
public class ProjectTask extends RealmObject {
    @PrimaryKey
    public ObjectId _id;
    @Required
    public String name;
    public String assignee;
    public int progressMinutes;
    public boolean isComplete;
    public int priority;
    @Required
    public String _partition;
}

Project.java

import org.bson.types.ObjectId;
import io.realm.RealmList;
import io.realm.RealmObject;
import io.realm.annotations.PrimaryKey;
import io.realm.annotations.RealmClass;
import io.realm.annotations.Required;
public class Project extends RealmObject {
    @PrimaryKey
    public ObjectId _id;
    @Required
    public String name;
    public RealmList<ProjectTask> tasks = new RealmList<>();
}

ProjectTask.kt

import io.realm.RealmObject
import io.realm.annotations.PrimaryKey
import io.realm.annotations.Required
import org.bson.types.ObjectId
open class ProjectTask(
    @PrimaryKey
    var _id: ObjectId = ObjectId(),
    @Required
    var name: String = "",
    var assignee: String? = null,
    var progressMinutes: Int = 0,
    var isComplete: Boolean = false,
    var priority: Int = 0,
    var _partition: String = ""
): RealmObject()

Project.kt

import io.realm.RealmList
import io.realm.RealmObject
import io.realm.annotations.PrimaryKey
import io.realm.annotations.Required
import org.bson.types.ObjectId
open class Project(
    @PrimaryKey
    var _id: ObjectId = ObjectId(),
    @Required
    var name: String = "",
    var tasks: RealmList<ProjectTask> = RealmList(),
): RealmObject()

修改对象

在事务中，您可以像更新所选语言中的任何其他对象一样更新 Realm 对象。只需为属性分配新值或更新属性即可。

以下示例将海龟的名称更改为“Archibald”，并通过为属性分配新值将阿奇博尔德的年龄设置为 101：

realm.executeTransaction(r -> {
    // Get a turtle to update.
    Turtle turtle = r.where(Turtle.class).findFirst();
    // Update properties on the instance.
    // This change is saved to the realm.
    turtle.setName("Archibald");
    turtle.setAge(101);
});

realm.executeTransaction { r: Realm ->
    // Get a turtle to update.
    val turtle = r.where(Turtle::class.java).findFirst()
    // Update properties on the instance.
    // This change is saved to the realm.
    turtle!!.name = "Archibald"
    turtle.age = 101
}

更新或插入（upsert）对象

更新或插入是一种写入操作，它可以插入具有给定主键的新对象，也可以更新已具有该主键的现有对象。我们将其称为更新或插入，因为它是“更新或插入”操作。当对象可能存在或不存在时（例如将数据集批量导入到现有域中），此功能非常有用。更新或插入是一种在添加新条目时更新现有条目的优雅方法。

以下示例演示了如何使用域更新或更新或插入（upsert）对象。我们创建一个名为“Drew”的新海龟爱好者，然后使用 insertOrUpdate()将其名称更新为“Andy”：

realm.executeTransaction(r -> {
    ObjectId id = new ObjectId();
    TurtleEnthusiast drew = new TurtleEnthusiast();
    drew.set_id(id);
    drew.setName("Drew");
    drew.setAge(25);
    // Add a new turtle enthusiast to the realm. Since nobody with this id
    // has been added yet, this adds the instance to the realm.
    r.insertOrUpdate(drew);
    TurtleEnthusiast andy = new TurtleEnthusiast();
    andy.set_id(id);
    andy.setName("Andy");
    andy.setAge(56);
    // Judging by the ID, it's the same turtle enthusiast, just with a different name.
    // As a result, you overwrite the original entry, renaming "Drew" to "Andy".
    r.insertOrUpdate(andy);
});

realm.executeTransaction { r: Realm ->
    val id = ObjectId()
    val drew = TurtleEnthusiast()
    drew._id = id
    drew.name = "Drew"
    drew.age = 25
    // Add a new turtle enthusiast to the realm. Since nobody with this id
    // has been added yet, this adds the instance to the realm.
    r.insertOrUpdate(drew)
    val andy = TurtleEnthusiast()
    andy._id = id
    andy.name = "Andy"
    andy.age = 56
    // Judging by the ID, it's the same turtle enthusiast, just with a different name.
    // As a result, you overwrite the original entry, renaming "Drew" to "Andy".
    r.insertOrUpdate(andy)
}

您还可以使用copyToRealmOrUpdate()根据提供的对象创建新对象，或更新具有相同主键的现有对象。使用CHECK_SAME_VALUES_BEFORE_SET ImportFlag仅更新所提供对象中不同的字段：

以下示例演示了如何插入一个对象，或者，如果已存在具有相同主键的对象，则仅更新那些不同的字段：

realm.executeTransaction(r -> {
    ObjectId id = new ObjectId();
    TurtleEnthusiast drew = new TurtleEnthusiast();
    drew.set_id(id);
    drew.setName("Drew");
    drew.setAge(25);
    // Add a new turtle enthusiast to the realm. Since nobody with this id
    // has been added yet, this adds the instance to the realm.
    r.insertOrUpdate(drew);
    TurtleEnthusiast andy = new TurtleEnthusiast();
    andy.set_id(id);
    andy.setName("Andy");
    // Judging by the ID, it's the same turtle enthusiast, just with a different name.
    // As a result, you overwrite the original entry, renaming "Drew" to "Andy".
    // the flag passed ensures that we only write the updated name field to the db
    r.copyToRealmOrUpdate(andy, ImportFlag.CHECK_SAME_VALUES_BEFORE_SET);
});

realm.executeTransaction { r: Realm ->
    val id = ObjectId()
    val drew = TurtleEnthusiast()
    drew._id = id
    drew.name = "Drew"
    drew.age = 25
    // Add a new turtle enthusiast to the realm. Since nobody with this id
    // has been added yet, this adds the instance to the realm.
    r.insertOrUpdate(drew)
    val andy = TurtleEnthusiast()
    andy._id = id
    andy.name = "Andy"
    // Judging by the ID, it's the same turtle enthusiast, just with a different name.
    // As a result, you overwrite the original entry, renaming "Drew" to "Andy".
    r.copyToRealmOrUpdate(andy,
        ImportFlag.CHECK_SAME_VALUES_BEFORE_SET)
}

更新collection

Realm 支持collection的更新。集合更新会同时将同一更新应用于集合中多个对象的特定属性。

以下示例演示了如何更新集合。由于 Turtle 的owner属性和 TurtleEnthusiast 的turtles属性之间存在隐式反向关系，因此当您使用setObject()更新集合中所有海龟的“所有者”属性时，Realm 会自动更新约瑟芬的海龟列表。

realm.executeTransaction(r -> {
    // Create a turtle enthusiast named Josephine.
    TurtleEnthusiast josephine = r.createObject(TurtleEnthusiast.class, new ObjectId());
    josephine.setName("Josephine");
    // Get all turtles named "Pierogi".
    RealmResults<Turtle> turtles = r.where(Turtle.class).equalTo("name", "Pierogi").findAll();
    // Give all turtles named "Pierogi" to Josephine
    turtles.setObject("owner", josephine);
});

realm.executeTransaction { r: Realm ->
    // Create a turtle enthusiast named Josephine.
    val josephine = realm.createObject(
        TurtleEnthusiast::class.java,
        ObjectId()
    )
    josephine.name = "Josephine"
    // Get all turtles named "Pierogi".
    val turtles = r.where(Turtle::class.java)
        .equalTo("name", "Pierogi")
        .findAll()
    // Give all turtles named "Pierogi" to Josephine
    turtles.setObject("owner", josephine)
}

迭代

由于域 collection始终反映最新状态，因此当您迭代collection时，它们可能会出现、消失或更改。要获得可迭代的稳定collection，可以创建collection数据的快照。快照可保证元素的顺序不会更改，即使删除或修改元素也是如此。

Iterator 从RealmResults创建的对象会自动使用快照。从RealmList实例创建的Iterator对象不使用快照。使用RealmList.createSnapshot() 或RealmResults.createSnapshot() 要手动生成快照，您可以手动迭代：

以下示例演示了如何使用从RealmResults Iterator创建的隐式快照或从RealmList创建的手动快照安全地迭代集合：

RealmResults<Frog> frogs = realm.where(Frog.class)
        .equalTo("species", "bullfrog")
        .findAll();
// Use an iterator to rename the species of all bullfrogs
realm.executeTransaction(r -> {
    for (Frog frog : frogs) {
        frog.setSpecies("Lithobates catesbeiana");
    }
});
// Use a snapshot to rename the species of all bullfrogs
realm.executeTransaction(r -> {
    OrderedRealmCollectionSnapshot<Frog> frogsSnapshot = frogs.createSnapshot();
    for (int i = 0; i < frogsSnapshot.size(); i++) {
        frogsSnapshot.get(i).setSpecies("Lithobates catesbeiana");
    }
});

val frogs = realm.where(Frog::class.java)
    .equalTo("species", "bullfrog")
    .findAll()
// Use an iterator to rename the species of all bullfrogs
realm.executeTransaction {
    for (frog in frogs) {
        frog.species = "Lithobates catesbeiana"
    }
}
// Use a snapshot to rename the species of all bullfrogs
realm.executeTransaction {
    val frogsSnapshot = frogs.createSnapshot()
    for (i in frogsSnapshot.indices) {
        frogsSnapshot[i]!!.species = "Lithobates catesbeiana"
    }
}

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