CRUD - Create - Java SDK

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About the Examples on this Page

Create a New Object

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About the Examples on this Page

The examples on this page use the data model of a project management app that has two Realm object types: Project and Task. A Project has zero or more Tasks.

See the schema for these two classes, Project and Task, below:

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()

Create a New Object

Use realm.createObject() in a transaction to create a persistent instance of a Realm object in a realm. You can then modify the returned object with other field values using accessors and mutators.

The following example demonstrates how to create an object with createObject():

realm.executeTransaction(r -> {
    // Instantiate the class using the factory function.
    Turtle turtle = r.createObject(Turtle.class, new ObjectId());
    // Configure the instance.
    turtle.setName("Max");
    // Create a TurtleEnthusiast with a primary key.
    ObjectId primaryKeyValue = new ObjectId();
    TurtleEnthusiast turtleEnthusiast = r.createObject(TurtleEnthusiast.class, primaryKeyValue);
});

realm.executeTransaction { r: Realm ->
    // Instantiate the class using the factory function.
    val turtle = r.createObject(Turtle::class.java, ObjectId())
    // Configure the instance.
    turtle.name = "Max"
    // Create a TurtleEnthusiast with a primary key.
    val primaryKeyValue = ObjectId()
    val turtleEnthusiast = r.createObject(
        TurtleEnthusiast::class.java,
        primaryKeyValue
    )
}

You can also insert objects into a realm from JSON. Realm supports creating objects from String, JSONObject, and InputStream types. Realm ignores any properties present in the JSON that are not defined in the Realm object schema.

The following example demonstrates how to create a single object from JSON with createObjectFromJson() or multiple objects from JSON with createAllFromJson():

// Insert from a string
realm.executeTransaction(new Realm.Transaction() {
    @Override
    public void execute(Realm realm) {
        realm.createObjectFromJson(Frog.class,
                "{ name: \"Doctor Cucumber\", age: 1, species: \"bullfrog\", owner: \"Wirt\" }");
    }
});
// Insert multiple items using an InputStream
realm.executeTransaction(new Realm.Transaction() {
    @Override
    public void execute(Realm realm) {
        try {
            InputStream inputStream = new FileInputStream(
                    new File("path_to_file"));
            realm.createAllFromJson(Frog.class, inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
});

// Insert from a string
realm.executeTransaction { realm ->
    realm.createObjectFromJson(
        Frog::class.java,
        "{ name: \"Doctor Cucumber\", age: 1, species: \"bullfrog\", owner: \"Wirt\" }"
    )
}
// Insert multiple items using an InputStream
realm.executeTransaction { realm ->
    try {
        val inputStream: InputStream =
            FileInputStream(File("path_to_file"))
        realm.createAllFromJson(Frog::class.java, inputStream)
    } catch (e: IOException) {
        throw RuntimeException(e)
    }
}

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