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How to retrieve data from Realm Database in Kotlin

How to retrieve data from Realm Database in Kotlin.

Here's a step-by-step tutorial on how to retrieve data from a Realm database in Kotlin:

Step 1: Add the Realm dependency​

To start using Realm in your Kotlin project, you need to add the Realm dependency to your app-level build.gradle file:

dependencies {
    implementation "io.realm:realm-android-library:10.7.0"
}

Step 2: Define a Realm model class​

Create a data class that represents the structure of your data in the Realm database. This class should extend the RealmObject class provided by Realm:

import io.realm.RealmObject

open class Person : RealmObject() {
    var name: String = ""
    var age: Int = 0
}

Step 3: Initialize the Realm instance​

To interact with the Realm database, you need to create an instance of the Realm class. You should do this in the onCreate method of your application class or in the onCreate method of your activity:

import io.realm.Realm

class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()
        Realm.init(this)
    }
}

Step 4: Retrieve data from the Realm database​

Once you have initialized the Realm instance, you can retrieve data from the Realm database using Realm queries. Here's an example of how to retrieve all Person objects from the database:

fun getAllPersons(): List<Person> {
    val realm = Realm.getDefaultInstance()
    val persons = realm.where(Person::class.java).findAll()
    return realm.copyFromRealm(persons)
}

In the code above, we first obtain the default Realm instance using Realm.getDefaultInstance(). Then, we create a query to retrieve all Person objects by calling realm.where(Person::class.java).findAll(). Finally, we use realm.copyFromRealm(persons) to copy the queried results from the Realm instance to a regular Kotlin list.

Step 5: Close the Realm instance​

After you have finished using the Realm instance, you should close it to release any resources it holds:

fun closeRealm() {
    val realm = Realm.getDefaultInstance()
    realm.close()
}

Closing the Realm instance is important to prevent memory leaks and ensure the proper functioning of your application.

That's it! You have successfully retrieved data from a Realm database in Kotlin. Remember to handle exceptions and errors appropriately when working with Realm, and make sure to follow the documentation for more advanced usage and features.