Room Persistence lib implementation in Kotlin

After spinning my head around for a while with this problem, I came across to the solution.

It was really hard as there is no official tutorial, blog etc out there to help with this problem as of now.

I had to do several hit and trial for all the combination of gradle plugins and dependencies as i knew that something is wrong with gradle config only.

Lets come to the solution:

I had to remove apply plugin: 'kotlin-kapt' from build.gradle(:module) file and replace annotationProcessor "android.arch.persistence.room:compiler:1.0.0-alpha1" to kapt "android.arch.persistence.room:compiler:1.0.0-alpha1".

This is the gradle configuration to successfully compile code.

But there more things to check. You have to initialise properties of your @Entity class unlike java given in Room Persistence lib doc. Though there are getter setter but it is not mentioned to create a constructor with initialisation. So I had to change my @Entity class with this:

@Entity(tableName = "all_food_list")
class Food (@ColumnInfo(name = "food_name") var foodName: String = "",
            @ColumnInfo(name = "food_desc") var foodDesc: String = "",
            @ColumnInfo(name = "protein") var protein: Double = 0.0,
            @ColumnInfo(name = "carbs") var carbs: Double = 0.0,
            @ColumnInfo(name = "fat") var fat: Double = 0.0,
            @ColumnInfo(name = "calories") var calories: Double = 0.0)
{
    @ColumnInfo(name = "id")
    @PrimaryKey(autoGenerate = true)
    var id: Long = 0
}

Now for TypeConverts, Unlike java, you need to create normal function not static functions(companion object):

class Converters{

        @TypeConverter
        fun fromTimestamp(value: String): Calendar {
            val arr = value.split("-")
            val cal = Calendar.getInstance()
            cal.set(arr[0].toInt(), arr[1].toInt(), arr[2].toInt())
            return cal
        }

        @TypeConverter
        fun dateToTimestamp(date: Calendar): String {
            return "${date.get(Calendar.DATE)}-${date.get(Calendar.MONTH)+1}-${date.get(Calendar.YEAR)}"
        }

}

I am adding build.gradle file also to make it more clear:

build.gradle(:project)

buildscript {
    ext.kotlin_version = '1.1.2-4'
    ext.gradle_version_stable = '2.3.2'
    ext.gradle_version_preview = '3.0.0-alpha1'
    ext.anko_version = '0.10.0'
    repositories {
        maven { url 'https://maven.google.com' }
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.0-alpha1'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        maven { url 'https://maven.google.com' }
        jcenter()
        maven { url "https://jitpack.io" }
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

build.gradle(:module)

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.2"
    defaultConfig {
        applicationId "com.chandilsachin.diettracker"
        minSdkVersion 16
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}


dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
    ...
    ...
    // room persistence dependency 
    compile "android.arch.persistence.room:runtime:1.0.0-alpha1"
    kapt "android.arch.persistence.room:compiler:1.0.0-alpha1"

    testCompile 'junit:junit:4.12'
}
repositories {
    mavenCentral()
}

I think this is all, I did to make my code woking.

Hope this helps someone else also.

Here my gradle files, i didn't need to add thoses plugins.

build.gradle(project):

buildscript {
    ext.kotlin_version = '1.1.2-4'
    ext.lifecycle_version = '1.0.0-alpha1'
    ext.room_version = '1.0.0-alpha1'

    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.2'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

    }
}

build.gradle (app)

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'

//enable anotation processing with kotlin, disabled by default
kapt {
    generateStubs = true
}


android {
/**
...
**/
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])

    //kotlin
    compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"

    //support
    compile 'com.android.support:appcompat-v7:25.3.1'

    //google architecture
    compile "android.arch.lifecycle:runtime:$lifecycle_version"
    compile "android.arch.lifecycle:extensions:$lifecycle_version"
    annotationProcessor "android.arch.lifecycle:compiler:$lifecycle_version"
    kapt "android.arch.lifecycle:compiler:$lifecycle_version"

    //database
    compile "android.arch.persistence.room:runtime:$room_version"
    annotationProcessor "android.arch.persistence.room:compiler:$room_version"
    kapt "android.arch.persistence.room:compiler:$room_version"

}
repositories {
    mavenCentral()
}

Then run menu build-> make project to create impl class. Hope this helps