Skip to main content

How to query data from Realm Database in Kotlin using RealmQuery

How to query data from Realm Database in Kotlin using RealmQuery.

Here's a step-by-step tutorial on how to query data from Realm Database in Kotlin using RealmQuery.

Step 1: Setup Realm in your project​

To use Realm Database in your Kotlin project, you need to add the necessary dependencies to your project's build.gradle file. Open your build.gradle file and add the following lines to the dependencies block:

implementation "io.realm:realm-android-library:10.8.0"
kapt "io.realm:realm-annotations-processor:10.8.0"

Sync your project to download the necessary dependencies.

Step 2: Create a Realm Model​

Before querying data from Realm, you need to define a Realm model class that represents the structure of your data. For example, let's say we want to query a list of Person objects. Create a new Kotlin class file called Person.kt and define the class as follows:

import io.realm.RealmObject

open class Person : RealmObject() {
    var name: String? = null
    var age: Int? = null
}

Step 3: Save data to Realm Database​

To query data, you first need to save some data to the Realm Database. In your Kotlin code, create a new instance of the Realm class and use it to save a Person object:

val realm = Realm.getDefaultInstance()

realm.executeTransaction { realm ->
    val person = realm.createObject(Person::class.java)
    person.name = "John Doe"
    person.age = 25
}

Step 4: Query data from Realm Database​

Now that you have some data saved in the Realm Database, you can query it using RealmQuery. Here are a few examples of how to query data:

Example 1: Retrieve all persons To retrieve all the Person objects from the Realm Database, you can use the findAll() method:

val realm = Realm.getDefaultInstance()

val persons = realm.where(Person::class.java).findAll()
for (person in persons) {
    println("Name: ${person.name}, Age: ${person.age}")
}

Example 2: Filter data based on a condition You can also filter the data based on a specific condition using the equalTo() method:

val realm = Realm.getDefaultInstance()

val persons = realm.where(Person::class.java).equalTo("age", 25).findAll()
for (person in persons) {
    println("Name: ${person.name}, Age: ${person.age}")
}

Example 3: Sorting the results You can sort the query results based on a specific field using the sort() method:

val realm = Realm.getDefaultInstance()

val persons = realm.where(Person::class.java).sort("age").findAll()
for (person in persons) {
    println("Name: ${person.name}, Age: ${person.age}")
}

Step 5: Close the Realm instance​

After you are done querying the data, make sure to close the Realm instance to release any resources:

realm.close()

That's it! You now know how to query data from Realm Database in Kotlin using RealmQuery. You can explore more advanced querying techniques in the Realm documentation.