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Comparing SQL Delight to Room Database in Android

February 1, 2022

There are several options when it comes to choosing a mobile database framework. We have the Room persistence library, Realm database, and SQL Delight.

Table of contents

Prerequisites

To follow along, you should have:

  • Android Studio installed on your machine.
  • Good knowledge of creating and running Android applications.
  • Basic knowledge of the Kotlin programming language and View binding.
  • A basic understanding of dependency injection with Dagger Hilt
  • Some basic understanding of ViewModels and Coroutines

Goals

By the end of this tutorial, the reader will:

  • Get to know what SQL Delight is.
  • Understand the pros and cons of SQL Delight.
  • Use SQL Delight in Android projects.

What is SQL delight database?

SQL delight is a database framework just like the Room library. It is cross-platform in nature and generates type-safe classes from the given SQL statements.

It checks on the database schema, migrations, and SQL statements at compile-time.

Pros of using SQL delight

  • It generates type-safe code and classes from the different SQL statements.
  • It is compatible with Kotlin Multi-platform (KMM) meaning we can use it in both IOS and Android.
  • SQL Delight is better when dealing with multi-table databases.

Cons of using SQL delight

  • We have to write more SQL code compared to the Room database library.

Getting started with SQL Delight

In this tutorial, we will be creating a simple Android note app with the SQL Delight library.

Step 1 - Create an Android project

Launch Android Studio and create an empty Android project, as shown below:

project

Step 2 - Setting up the project

In this step, we will do all the necessary setup for our project.

Add the following plugins in your app-level build.gradle file:

id 'com.squareup.sqldelight'
id 'kotlin-kapt'
id 'dagger.hilt.android.plugin'

Still in your app-level build.gradle file, add the following dependencies:

// SQL Delight
implementation "com.squareup.sqldelight:android-driver:1.5.2"
implementation "com.squareup.sqldelight:coroutines-extensions-jvm:1.5.2"

// Coroutines
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.5.2'
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.5.2'

// Dagger - Hilt
implementation "com.google.dagger:hilt-android:2.38.1"
kapt "com.google.dagger:hilt-android-compiler:2.38.1"
implementation 'androidx.hilt:hilt-navigation-fragment:1.0.0'

// ViewModel
implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.4.0'

In your project-level build.gradle file, add the following classpaths:

classpath 'com.squareup.sqldelight:gradle-plugin:1.5.2'
classpath "com.google.dagger:hilt-android-gradle-plugin:2.38.1"

We then need to install the SQLDelight plugin in our Android Studio. It generates typesafe Kotlin APIs from SQL, and provides language features for SQL inside the IDE.

Open your Android Studio » Settings » Plugins, then click on the marketplace and search for the plugin:

plugin

Step 3 - Defining the database

In our app-level build.gradle, we need to add some settings that notify SQL Delight where it should generate our database and how it should be named.

Inside the sqldelight block, we define the name of our database and pass the app’s package name that specifies where the database belongs:

dependencies {
    ...
}

sqldelight {
    NotesDatabase {
        packageName = "com.sheecodes.sqldelightdemo"
    }
}

Step 4 - Defining the SQL queries

First, switch from Android view to Project view. Since the files that define our SQL queries need to be defined in the main source set, we will add the SQL delight file in the main package.

Right-click the main package and create a directory named sqldelight and then add two other directories i.e sqldelight/demo/notesdb.

Right-click the notesdb directory and using the SQLDelight plugin, create an SQL Delight table.

Enter the name of our table notesEntity and select table from the options:

new_table

It should generate something like this:

CREATE TABLE  notesEntity(

);

The way you define tables in SQL is the same in SQL Delight. We can go ahead and add an id, title, and description in our table.

CREATE TABLE  notesEntity(
    id INTEGER NOT NULL PRIMARY KEY,
    title TEXT NOT NULL,
    description TEXT NOT NULL
);

SQL Delight will use this code to generate a type-safe kotlin code for us.

To include more queries or tables, you can define a new SQL file or just add them below the existing one.

Below our table, we will define the CRUD operations that our app will use i.e insert, read, update and delete.

We first write the function name followed by the SQL statement that should be executed when the function is called.

getNoteById: SELECT * FROM notesEntity WHERE id = :id;

getAllNotes: SELECT * FROM notesEntity;

insertNote: INSERT OR REPLACE INTO notesEntity VALUES (?,?,?);

deletePersonById: DELETE FROM notesEntity WHERE id = :id;

We should now rebuild the project so that SQL Delight can generate the corresponding classes.

Step 5 - Defining the data source

First of all, switch from project view to Android view. In your root package define a new package named data.

In the new directory, define an Interface and name it NoteDataSource. This interface will contain functions that will help us interact with the database.

interface NoteDataSource {
    suspend fun insertNote(title: String, description: String,id: Long? = null)

    fun getAllNotes(): Flow<List<NotesEntity>>

    suspend fun getNoteById(id: Long): NotesEntity?

    suspend fun deleteNoteById(id: Long)
}

The first function, getAllNotes, returns a NotesEntity which is a class generated by the SQLDelight behind the scenes.

Still, inside the data package, we need to create an implementation of the NoteDataSource. Create a new Kotlin class NoteDataSourceImpl that extends the NoteDataSource.

The class will take a reference to our database - NotesDatabase as its parameters in its constructor.

As you can remember in our app-level build.gradle, we defined our database that was then generated by SQLDelight.

class NoteDataSourceImpl(db: NotesDatabase) : NoteDataSource {
    ...
}

Inside this class, we define an object that contains the reference to our notesEntity queries:

private val queries = db.notesEntityQueries

We then add the implementations of the following functions inside the class:

Inserting a note

override suspend fun insertNote(title: String, description: String, id: Long?) {
    return withContext(Dispatchers.IO) {
        queries.insertNote(id, title, description)
    }
}

Getting all notes

override fun getAllNotes(): Flow<List<NotesEntity>> {
    return queries.getAllNotes().asFlow().mapToList()
}

Since we are returning a Flow of a list of notes, there is a function in SQLDelight called asFlow() that we can append at the end of our query. Still, there will be an error, we simply append mapToList() to fix it.

Getting a note by id

override suspend fun getNoteById(id: Long): NotesEntity? {
    return withContext(Dispatchers.IO) {
        queries.getNoteById(id).executeAsOneOrNull()
    }
}

At the end of the query we append the executeAsOneOrNull() because our query may return a null if the note is not found in the database.

Deleting a note

override suspend fun deleteNoteById(id: Long) {
    return withContext(Dispatchers.IO) {
        queries.deletePersonById(id)
    }
}

Here, we pass the id of the note that we wish to delete.

Step 6 - Defining a viewmodel

In this step, we define a ViewModel that will interact with the data source that we have just created.

@HiltViewModel
class NotesViewModel @Inject constructor(private val noteDataSource: NoteDataSource): ViewModel() {

    val notes = noteDataSource.getAllNotes()
    var noteDetails = MutableLiveData<NotesEntity>()

    fun insertNote(title: String, description: String){
        if (title.isNullOrEmpty() || description.isNullOrEmpty()){
            return
        }

        viewModelScope.launch {
            noteDataSource.insertNote(title, description)
        }
    }

    fun deleteNote(id: Long){
        viewModelScope.launch {
            noteDataSource.deleteNoteById(id)
        }
    }

    fun getNoteById(id: Long){
        viewModelScope.launch {
            noteDetails.value = noteDataSource.getNoteById(id)
        }
    }
}

Step 7 - Setting up dagger hilt

Here we will set up dagger hilt so that we can inject our data source and the database.

First, in your root package, create a class named NotesApp and add hilt as follows:

@HiltAndroidApp
class NotesApp : Application()

Don’t forget to specify the class as a name in your manifest file.

Define another package and name it di. Right-click on the package and create a new object file called AppModule:

@Module
@InstallIn(SingletonComponent::class)
object AppModule {
    ...
}

We then provide the following dependencies:

  1. Database Driver

SQLDelight needs the AndroidSqliteDriver so that it can create and use the database. Inside the AndroidSqliteDriver, we pass the schema (generated), context, and the name of our database, as demonstrated below:

@Provides
@Singleton
fun provideSqlDriver(app: Application): SqlDriver {
    return AndroidSqliteDriver(
        schema = NotesDatabase.Schema,
        context = app,
        name = "notes.db"
    )
}
  1. Data source

Using the driver above, we can construct the data source, as follows:

@Provides
@Singleton
fun providesNotesDataSource(driver: SqlDriver): NoteDataSource {
    return NoteDataSourceImpl(
        NotesDatabase(driver)
    )
}

Step 8 - Working on the activities

Finally, we will define our user activities, one for adding notes and another one for displaying a list of notes.

Adding notes

You can create a similar layout that has two EditText: one for note title and another one for note description and button to save the note.

add_note

In the corresponding activity, add the following code to save a note when the save button is clicked:

binding.buttonSave.setOnClickListener {
    val title = binding.edtTitle.text.toString()
    val description = binding.edtDescription.text.toString()

    if (title.isNullOrEmpty() || description.isNullOrEmpty()){
        return@setOnClickListener
    }

    CoroutineScope(Dispatchers.Main).launch {
        viewModel.insertNote(title, description)
        startActivity(Intent(this@AddNoteActivity, MainActivity::class.java))
        finish()
    }
}

Displaying notes

Create a similar layout that has a Recyclerview for displaying the list of notes.

notes_list

Don’t forget to create a corresponding row layout for the Recyclerview.

Also, make sure you have defined an adapter that your Recyclerview will use. The model class that the adapter will use will be the NotesEntity that was generated by SQLDelight.

In the corresponding activity, add the following code to display the notes:

CoroutineScope(Dispatchers.Main).launch {
    viewModel.notes.collect { notes ->
        adapter.submitList(notes)
        binding.notesRecycler.adapter = adapter
    }
}

Deleting a note

If you have set onClickListeners to your Recyclerview items, you can call the delete method from the ViewModel, this way:

viewModel.deleteNote(note.id)

Updating a note

If you want to update a note from the function getNoteById(id: Long) in the ViewModel, you pass in its id.

Demo

demo

Conclusion

In this tutorial, we have discussed what SQL Delight database is, how it compares to the Room database, and its pros and cons.

We have then implemented the SQL Delight database in Android by creating a simple note app.

To get the full code implementation, check out this repository SQL Delight Demo.

Further reading


Peer Review Contributions by: Eric Gacoki