Mastering Kotlin: Creating an API With Ktor and MongoDB Atlas

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fitness {
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    _id: objectId,
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    exerciseType: String,
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    notes: String,
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    fitnessDetails: {
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        durationMinutes: Int,
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        distance: Double,
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        caloriesBurned: Int
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    }
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}

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dependencies {
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    implementation("io.ktor:ktor-server-core-jvm")
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    implementation("io.ktor:ktor-server-swagger-jvm")
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    implementation("io.ktor:ktor-server-content-negotiation-jvm")
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    implementation("io.ktor:ktor-serialization-gson-jvm")
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    implementation("io.ktor:ktor-server-tomcat-jvm")
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    implementation("ch.qos.logback:logback-classic:$logback_version")
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    //MongoDB
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    implementation("org.mongodb:mongodb-driver-kotlin-coroutine:4.10.1")
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    //Koin Dependency Injection
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    implementation("io.insert-koin:koin-ktor:3.5.3")
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    implementation("io.insert-koin:koin-logger-slf4j:3.5.3")
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}

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package com.mongodb.domain.entity
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import com.mongodb.application.response.FitnessResponse
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import org.bson.codecs.pojo.annotations.BsonId
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import org.bson.types.ObjectId
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data class Fitness(
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    @BsonId
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    val id: ObjectId,
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    val exerciseType: String,
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    val notes: String,
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    val details: FitnessDetails
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){
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    fun toResponse() = FitnessResponse(
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        id = id.toString(),
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        exerciseType = exerciseType,
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        notes = notes,
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        details = details
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    )
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}
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data class FitnessDetails(
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    val durationMinutes: Int,
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    val distance: Double,
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    val caloriesBurned: Int
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)

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package com.mongodb.application.request
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import com.mongodb.domain.entity.Fitness
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import com.mongodb.domain.entity.FitnessDetails
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import org.bson.types.ObjectId
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data class FitnessRequest(
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    val exerciseType: String,
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    val notes: String,
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    val details: FitnessDetails
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)
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fun FitnessRequest.toDomain(): Fitness {
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    return Fitness(
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        id = ObjectId(),
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        exerciseType = exerciseType,
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        notes = notes,
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        details = details
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    )
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}

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package com.mongodb.application.response
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import com.mongodb.domain.entity.FitnessDetails
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data class FitnessResponse(
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    val id: String,
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    val exerciseType: String,
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    val notes: String,
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    val details: FitnessDetails
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)

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package com.mongodb.domain.ports
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import com.mongodb.domain.entity.Fitness
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import org.bson.BsonValue
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import org.bson.types.ObjectId
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interface FitnessRepository {
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    suspend fun insertOne(fitness: Fitness): BsonValue?
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    suspend fun deleteById(objectId: ObjectId): Long
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    suspend fun findById(objectId: ObjectId): Fitness?
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    suspend fun updateOne(objectId: ObjectId, fitness: Fitness): Long
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}

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package com.mongodb.infrastructure.repository
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import com.mongodb.MongoException
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import com.mongodb.client.model.Filters
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import com.mongodb.client.model.UpdateOptions
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import com.mongodb.client.model.Updates
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import com.mongodb.domain.entity.Fitness
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import com.mongodb.domain.ports.FitnessRepository
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import com.mongodb.kotlin.client.coroutine.MongoDatabase
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import kotlinx.coroutines.flow.firstOrNull
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import org.bson.BsonValue
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import org.bson.types.ObjectId
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class FitnessRepositoryImpl(
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    private val mongoDatabase: MongoDatabase
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) : FitnessRepository {
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    companion object {
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        const val FITNESS_COLLECTION = "fitness"
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    }
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    override suspend fun insertOne(fitness: Fitness): BsonValue? {
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        try {
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            val result = mongoDatabase.getCollection<Fitness>(FITNESS_COLLECTION).insertOne(
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                fitness
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            )
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            return result.insertedId
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        } catch (e: MongoException) {
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            System.err.println("Unable to insert due to an error: $e")
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        }
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        return null
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    }
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    override suspend fun deleteById(objectId: ObjectId): Long {
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        try {
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            val result = mongoDatabase.getCollection<Fitness>(FITNESS_COLLECTION).deleteOne(Filters.eq("_id", objectId))
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            return result.deletedCount
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        } catch (e: MongoException) {
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            System.err.println("Unable to delete due to an error: $e")
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        }
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        return 0
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    }
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    override suspend fun findById(objectId: ObjectId): Fitness? =
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    mongoDatabase.getCollection<Fitness>(FITNESS_COLLECTION).withDocumentClass<Fitness>()
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    .find(Filters.eq("_id", objectId))
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    .firstOrNull()
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    override suspend fun updateOne(objectId: ObjectId, fitness: Fitness): Long {
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        try {
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            val query = Filters.eq("_id", objectId)
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            val updates = Updates.combine(
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                Updates.set(Fitness::exerciseType.name, fitness.exerciseType),
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                Updates.set(Fitness::notes.name, fitness.notes),
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                Updates.set(Fitness::details.name, fitness.details)
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            )
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            val options = UpdateOptions().upsert(true)
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            val result =
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            mongoDatabase.getCollection<Fitness>(FITNESS_COLLECTION)
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            .updateOne(query, updates, options)
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            return result.modifiedCount
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        } catch (e: MongoException) {
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            System.err.println("Unable to update due to an error: $e")
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        }
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        return 0
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    }
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}

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package com.mongodb.application.routes
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import com.mongodb.application.request.FitnessRequest
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import com.mongodb.application.request.toDomain
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import com.mongodb.domain.ports.FitnessRepository
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import io.ktor.http.HttpStatusCode
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import io.ktor.server.application.call
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import io.ktor.server.request.receive
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import io.ktor.server.response.respond
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import io.ktor.server.response.respondText
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import io.ktor.server.routing.route
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import io.ktor.server.routing.Route
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import io.ktor.server.routing.post
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import io.ktor.server.routing.delete
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import io.ktor.server.routing.get
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import io.ktor.server.routing.patch
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import org.bson.types.ObjectId
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import org.koin.ktor.ext.inject
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fun Route.fitnessRoutes() {
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    val repository by inject<FitnessRepository>()
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    route("/fitness") {
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        post {
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            val fitness = call.receive<FitnessRequest>()
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            val insertedId = repository.insertOne(fitness.toDomain())
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            call.respond(HttpStatusCode.Created, "Created fitness with id $insertedId")
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        }
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        delete("/{id?}") {
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            val id = call.parameters["id"] ?: return@delete call.respondText(
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                text = "Missing fitness id",
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                status = HttpStatusCode.BadRequest
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            )
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            val delete: Long = repository.deleteById(ObjectId(id))
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            if (delete == 1L) {
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                return@delete call.respondText("Fitness Deleted successfully", status = HttpStatusCode.OK)
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            }
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            return@delete call.respondText("Fitness not found", status = HttpStatusCode.NotFound)
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        }
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        get("/{id?}") {
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            val id = call.parameters["id"]
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            if (id.isNullOrEmpty()) {
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                return@get call.respondText(
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                    text = "Missing id",
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                    status = HttpStatusCode.BadRequest
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                )
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            }
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            repository.findById(ObjectId(id))?.let {
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                call.respond(it.toResponse())
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            } ?: call.respondText("No records found for id $id")
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        }
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        patch("/{id?}") {
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            val id = call.parameters["id"] ?: return@patch call.respondText(
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                text = "Missing fitness id",
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                status = HttpStatusCode.BadRequest
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            )
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            val updated = repository.updateOne(ObjectId(id), call.receive())
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            call.respondText(
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                text = if (updated == 1L) "Fitness updated successfully" else "Fitness not found",
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                status = if (updated == 1L) HttpStatusCode.OK else HttpStatusCode.NotFound
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            )
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        }
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    }
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}

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package com.mongodb
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import com.mongodb.application.routes.fitnessRoutes
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import com.mongodb.domain.ports.FitnessRepository
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import com.mongodb.infrastructure.repository.FitnessRepositoryImpl
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import com.mongodb.kotlin.client.coroutine.MongoClient
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import io.ktor.serialization.gson.gson
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import io.ktor.server.application.Application
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import io.ktor.server.application.install
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import io.ktor.server.plugins.contentnegotiation.ContentNegotiation
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import io.ktor.server.plugins.swagger.swaggerUI
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import io.ktor.server.routing.routing
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import io.ktor.server.tomcat.EngineMain
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import org.koin.dsl.module
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import org.koin.ktor.plugin.Koin
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import org.koin.logger.slf4jLogger
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fun main(args: Array<String>): Unit = EngineMain.main(args)
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fun Application.module() {
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    install(ContentNegotiation) {
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        gson {
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        }
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    }
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    install(Koin) {
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        slf4jLogger()
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        modules(module {
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            single { MongoClient.create(
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                environment.config.propertyOrNull("ktor.mongo.uri")?.getString() ?: throw RuntimeException("Failed to access MongoDB URI.")
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            ) }
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            single { get<MongoClient>().getDatabase(environment.config.property("ktor.mongo.database").getString()) }
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        }, module {
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            single<FitnessRepository> { FitnessRepositoryImpl(get()) }
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        })
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    }
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    routing {
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        swaggerUI(path = "swagger-ui", swaggerFile = "openapi/documentation.yaml") {
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            version = "4.15.5"
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        }
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        fitnessRoutes()
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    }
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}

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ktor {
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    deployment {
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        port = 8080
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    }
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    application {
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        modules = [ com.mongodb.ApplicationKt.module ]
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    }
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    mongo {
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        uri = ${?MONGO_URI}
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        database = ${?MONGO_DATABASE}
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    }
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}

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openapi: 3.0.0
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info:
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 title: Fitness API
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 version: 1.0.0
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 description: |
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   This Swagger documentation file outlines the API specifications for a Fitness Tracker application built with Ktor and MongoDB. The API allows users to manage fitness records including creating new records, updating and deleting records by ID. The API uses the Fitness and FitnessDetails data classes to structure the fitness-related information.
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paths:
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 /fitness:
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   post:
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     summary: Create a new fitness record
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     requestBody:
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       required: true
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       content:
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         application/json:
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           schema:
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             $ref: '#/components/schemas/FitnessRequest'
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     responses:
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       '201':
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         description: Fitness created successfully
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       '400':
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         description: Bad request
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 /fitness/{id}:
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   get:
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     summary: Retrieve fitness record by ID
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     parameters:
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       - name: id
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         in: path
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         required: true
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         schema:
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           type: string
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     responses:
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       '200':
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         description: Successful response
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         content:
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           application/json:
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             example: {}
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       '404':
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         description: Fitness not found
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   delete:
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     summary: Delete fitness record by ID
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     parameters:
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       - name: id
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         in: path
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         required: true
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         schema:
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           type: string
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     responses:
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       '200':
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         description: Fitness deleted successfully
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       '400':
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         description: Bad request
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       '404':
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         description: Fitness not found
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   patch:
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     summary: Update fitness record by ID
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     parameters:
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       - name: id
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         in: path
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         required: true
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         schema:
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           type: string
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     requestBody:
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       required: true
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       content:
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         application/json:
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           schema:
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             $ref: '#/components/schemas/FitnessRequest'
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     responses:
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       '200':
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         description: Fitness updated successfully
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       '400':
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         description: Bad request
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       '404':
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         description: Fitness not found
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components:
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 schemas:
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   Fitness:
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     type: object
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     properties:
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       id:
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         type: string
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         format: uuid
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       exerciseType:
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         type: string
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       notes:
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         type: string
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       details:
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         $ref: '#/components/schemas/FitnessDetails'
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     required:
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       - id
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       - notes
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       - details
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   FitnessDetails:
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     type: object
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     properties:
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       durationMinutes:
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         type: integer
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         format: int32
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       distance:
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         type: number
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         format: double
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       caloriesBurned:
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         type: integer
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         format: int32
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     required:
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       - durationMinutes
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       - distance
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       - caloriesBurned
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   FitnessRequest:
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     type: object
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     properties:
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       exerciseType:
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         type: string
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       notes:
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         type: string
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       details:
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         $ref: '#/components/schemas/FitnessDetails'
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     required:
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       - exerciseType
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       - notes
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       - details

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-DMONGO_URI= Add your connection string
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-DMONGO_DATABASE= Add your database name