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How to delete data from Realm Database in Kotlin

How to delete data from Realm Database in Kotlin.

Here is a step-by-step tutorial on how to delete data from a Realm Database in Kotlin:

Step 1: Add Realm library to your project​

First, you need to add the Realm library to your project. Open your project's build.gradle file and add the following dependency:

implementation 'io.realm:realm-android'

Step 2: Initialize Realm​

Next, you need to initialize the Realm in your application's entry point. This is usually done in the onCreate method of your Application class. Add the following code to initialize Realm:

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

Don't forget to update your manifest file to use this custom Application class.

Step 3: Define a Realm model​

To delete data from the Realm database, you need to have a model class that represents the data you want to delete. Create a Kotlin data class that extends the RealmObject class and define the fields you want to store. For example:

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

Step 4: Delete data from Realm​

To delete data from Realm, you need to open a Realm instance, start a write transaction, and then delete the desired objects. Here's an example of how to delete a single object:

// Open a Realm instance
val realm = Realm.getDefaultInstance()

// Start a write transaction
realm.beginTransaction()

// Find the object you want to delete
val personToDelete = realm.where(Person::class.java).equalTo("id", "123").findFirst()

// Delete the object
personToDelete?.deleteFromRealm()

// Commit the transaction
realm.commitTransaction()

// Close the Realm instance
realm.close()

In the above example, we open a Realm instance using Realm.getDefaultInstance(), start a write transaction using realm.beginTransaction(), find the object we want to delete using a query, delete the object using deleteFromRealm(), and then commit the transaction using realm.commitTransaction(). Finally, we close the Realm instance using realm.close().

Step 5: Delete multiple objects​

If you want to delete multiple objects, you can use the realm.where() method with a query to find the objects you want to delete, and then delete them one by one or all at once. Here's an example of how to delete multiple objects:

// Open a Realm instance
val realm = Realm.getDefaultInstance()

// Start a write transaction
realm.beginTransaction()

// Find the objects you want to delete
val personsToDelete = realm.where(Person::class.java).equalTo("age", 25).findAll()

// Delete the objects one by one
for (person in personsToDelete) {
    person.deleteFromRealm()
}

// Alternatively, delete all objects at once
personsToDelete.deleteAllFromRealm()

// Commit the transaction
realm.commitTransaction()

// Close the Realm instance
realm.close()

In the above example, we find the objects to delete using a query (equalTo("age", 25)), and then delete them one by one using a loop or delete all at once using deleteAllFromRealm().

That's it! You have successfully learned how to delete data from a Realm Database in Kotlin.