hkakutalua

Taming Recursion - An Introduction

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Recursion, which ends up being way simpler for some problems, can seem very hard for you to wrap your head around, or to follow down the recursive rabbit-hole to understand how it produces the values it does (spoiler: doing this may be a mistake).

But do not despair, I'm here to help you learn a very good framework to think recursively in any programming language and almost any problem.

Every code example will be in Scala a programming language that combines the object-oriented and functional programming paradigms. It will be very straightforward to translate the examples from Scala to your language of choice since the syntax is very much approachable.

hkakutalua

Chat Application

A very simple instant messaging application to practice Scala, Kafka, and Docker.

Features

Enter Chat Room

The user should be able to enter the chat room with its id name, name and age. The id name it is used so he can be persisted temporarily to later reenter to read messages not yet read.

Leave Chat Room

The user should be able to leaver the chat room.

hkakutalua

@Configuration
@EnableSwagger2
public class SpringFoxConfiguration {
    @Bean
    @Primary
    public Docket swaggerSpringfoxApiDocket(List<SwaggerCustomizer> swaggerCustomizers,
                                            ObjectProvider<AlternateTypeRule[]> alternateTypeRules) {
        Docket docket = new Docket(DocumentationType.SWAGGER_2)
            .select()
            .apis(RequestHandlerSelectors.any())

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@Entity
@Table(name = "carts")
class Cart : DomainEntity() {
    @OneToMany(fetch = FetchType.EAGER, cascade = [CascadeType.ALL], orphanRemoval = true)
    private val _items = mutableListOf<ProductItem>()
    
    ...
    
}

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@Throws(SQLException::class)
private fun cleanTablesData(tablesNames: List<TableData>, connection: Connection) {
    if (tablesNames.isEmpty()) {
        return
    }
    val stringBuilder = StringBuilder("TRUNCATE ")
    for (i in tablesNames.indices) {
        if (i == 0) {
            stringBuilder.append(tablesNames[i].fullyQualifiedTableName)
        } else {

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@Throws(SQLException::class)
private fun loadTablesToClean(connection: Connection): List<TableData> {
    val databaseMetaData = connection.metaData
    val resultSet = databaseMetaData.getTables(
        connection.catalog, null, null, arrayOf("TABLE"))

    val tablesToClean = mutableListOf<TableData>()
    while (resultSet.next()) {
        val table = TableData(
            schema = resultSet.getString("TABLE_SCHEM"),

hkakutalua

class PostgresDbCleanerExtension : BeforeEachCallback {
    companion object {
        private val LOGGER = LoggerFactory.getLogger(PostgresDbCleanerExtension::class.java)

        private val TABLES_TO_IGNORE = listOf(
            TableData("databasechangelog"),
            TableData("databasechangeloglock")
        )
    }

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@SpringBootTest
@ExtendWith(PostgresDbCleanerExtension::class)
internal class CartsControllerTests {
    @Autowired
    lateinit var cartsRepository: CartsRepository

    @Autowired
    lateinit var webApplicationContext: WebApplicationContext
    
    ...

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@RestController
@RequestMapping("carts/{cart_id}/items")
class CartItemsController(
    private val cartsRepository: CartsRepository,
    private val productsRepository: ProductsRepository) {

    @PostMapping
    fun addItemToCart(
        @PathVariable("cart_id") cartId: UUID,
        @RequestBody cartItem: CartItemInputModel

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val product =  productsRepository.findByIdOrNull(cartItem.productId)
if (product == null) {
    return ResponseEntity.notFound().build()
}

val cart = cartsRepository.findByIdOrNull(cartId)
if (cart == null) {
    return ResponseEntity.notFound().build()
}