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Add Kotlin example for Spring Data Cassandra.
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‎cassandra/kotlin/README.md

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# Spring Data Cassandra - Kotlin examples
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This project contains samples of Kotlin-specific features of Spring Data (Cassandra).
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## Value defaulting on entity construction
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Kotlin allows defaulting for constructor- and method arguments.
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Defaulting allows usage of substitute values if a field in the document is absent or simply `null`.
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Spring Data inspects objects whether they are Kotlin types and uses the appropriate constructor.
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```kotlin
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@Table
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data class Person(@PrimaryKeyColumn(type = PrimaryKeyType.PARTITIONED) val firstname: String? = "", val lastname: String = "White")
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operations.cqlOperations.execute(QueryBuilder.insertInto("person").value("firstname", "Walter"))
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val person = operations.query<Person>()
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.matching(query(where("firstname").isEqualTo("Walter")))
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.firstValue()!!
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assertThat(person.lastname).isEqualTo("White")
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```
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## Kotlin Extensions
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Spring Data exposes methods accepting a target type to either query for or to project results values on.
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Kotlin represents classes with its own type, `KClass` which can be an obstacle when attempting to obtain a Java `Class` type.
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Spring Data ships with extensions that add overloads for methods accepting a type parameter by either leveraging generics or accepting `KClass` directly.
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```kotlin
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operations.getTableName<Person>()
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operations.getTableName(Person::class)
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```
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## Nullability
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Declaring repository interfaces using Kotlin allows expressing nullability constraints on arguments and return types. Spring Data evaluates nullability of arguments and return types and reacts to these. Passing `null` to a non-nullable argument raises an `IllegalArgumentException`, as you're already used to from Kotlin. Spring Data helps you also to prevent `null` in query results. If you wish to return a nullable result, use Kotlin's nullability marker `?`. To prevent `null` results, declare the return type of a query method as non-nullable. In the case a query yields no result, a non-nullable query method throws `EmptyResultDataAccessException`.
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```kotlin
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interface PersonRepository : CrudRepository<Person, String> {
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/**
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* Query method declaring a nullable return type that allows to return null values.
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*/
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fun findOneOrNoneByFirstname(firstname: String): Person?
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/**
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* Query method declaring a nullable argument.
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*/
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fun findNullableByFirstname(firstname: String?): Person?
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/**
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* Query method requiring a result. Throws [org.springframework.dao.EmptyResultDataAccessException] if no result is found.
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*/
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fun findOneByFirstname(firstname: String): Person
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}
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```

‎cassandra/kotlin/pom.xml

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>org.springframework.data.examples</groupId>
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<artifactId>spring-data-cassandra-examples</artifactId>
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<version>2.0.0.BUILD-SNAPSHOT</version>
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</parent>
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<artifactId>spring-data-cassandra-kotlin</artifactId>
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<name>Spring Data Cassandra - Kotlin features</name>
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<properties>
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<spring-data-releasetrain.version>Lovelace-BUILD-SNAPSHOT</spring-data-releasetrain.version>
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</properties>
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<profiles>
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<!-- Override property as the module always needs Lovelace -->
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<profile>
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<id>spring-data-next</id>
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<properties>
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<spring-data-releasetrain.version>Lovelace-BUILD-SNAPSHOT</spring-data-releasetrain.version>
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</properties>
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</profile>
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</profiles>
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<dependencies>
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<dependency>
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<groupId>org.jetbrains.kotlin</groupId>
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<artifactId>kotlin-stdlib-jdk8</artifactId>
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</dependency>
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<dependency>
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<groupId>org.jetbrains.kotlin</groupId>
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<artifactId>kotlin-reflect</artifactId>
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</dependency>
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<dependency>
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<groupId>${project.groupId}</groupId>
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<artifactId>spring-data-cassandra-example-utils</artifactId>
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<version>${project.version}</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<sourceDirectory>${project.basedir}/src/main/kotlin</sourceDirectory>
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<testSourceDirectory>${project.basedir}/src/test/kotlin</testSourceDirectory>
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<plugins>
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<plugin>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-maven-plugin</artifactId>
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</plugin>
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<plugin>
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<artifactId>kotlin-maven-plugin</artifactId>
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<groupId>org.jetbrains.kotlin</groupId>
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<configuration>
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<args>
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<arg>-Xjsr305=strict</arg>
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</args>
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<compilerPlugins>
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<plugin>spring</plugin>
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</compilerPlugins>
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</configuration>
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<dependencies>
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<dependency>
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<groupId>org.jetbrains.kotlin</groupId>
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<artifactId>kotlin-maven-allopen</artifactId>
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<version>${kotlin.version}</version>
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</dependency>
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</dependencies>
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</plugin>
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</plugins>
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</build>
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</project>

‎cassandra/kotlin/src/main/kotlin/example.springdata.cassandra.kotlin/ApplicationConfiguration.kt

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/*
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* Copyright 2018 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package example.springdata.cassandra.kotlin
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import org.springframework.boot.autoconfigure.SpringBootApplication
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import org.springframework.boot.runApplication
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/**
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* @author Mark Paluch
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*/
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@SpringBootApplication
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class ApplicationConfiguration
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fun main(args: Array<String>) {
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runApplication<ApplicationConfiguration>(*args)
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}

‎cassandra/kotlin/src/main/kotlin/example.springdata.cassandra.kotlin/Person.kt

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/*
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* Copyright 2018 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package example.springdata.cassandra.kotlin
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import org.springframework.data.cassandra.core.cql.PrimaryKeyType
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import org.springframework.data.cassandra.core.mapping.PrimaryKeyColumn
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import org.springframework.data.cassandra.core.mapping.Table
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/**
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* An entity to represent a Person.
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*
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* @author Mark Paluch
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*/
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@Table
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data class Person(@PrimaryKeyColumn(type = PrimaryKeyType.PARTITIONED) val firstname: String? = "", val lastname: String = "White")

‎cassandra/kotlin/src/main/kotlin/example.springdata.cassandra.kotlin/PersonRepository.kt

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/*
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* Copyright 2018 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package example.springdata.cassandra.kotlin
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import org.springframework.data.repository.CrudRepository
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/**
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* Repository interface to manage [Person] instances.
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*
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* @author Mark Paluch
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*/
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interface PersonRepository : CrudRepository<Person, String> {
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/**
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* Query method declaring a nullable return type that allows to return null values.
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*/
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fun findOneOrNoneByFirstname(firstname: String): Person?
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/**
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* Query method declaring a nullable argument.
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*/
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fun findNullableByFirstname(firstname: String?): Person?
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/**
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* Query method requiring a result. Throws [org.springframework.dao.EmptyResultDataAccessException] if no result is found.
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*/
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fun findOneByFirstname(firstname: String): Person
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}

‎cassandra/kotlin/src/main/resources/application.properties

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spring.data.cassandra.keyspace-name=example
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spring.data.cassandra.schema-action=recreate

‎cassandra/kotlin/src/test/kotlin/example/springdata/cassandra/kotlin/RepositoryTests.kt

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/*
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* Copyright 2018 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package example.springdata.cassandra.kotlin
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import example.springdata.cassandra.util.CassandraKeyspace
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import org.assertj.core.api.Assertions.assertThat
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import org.assertj.core.api.Assertions.assertThatThrownBy
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import org.junit.Before
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import org.junit.ClassRule
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import org.junit.Test
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import org.junit.runner.RunWith
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import org.springframework.beans.factory.annotation.Autowired
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import org.springframework.boot.test.context.SpringBootTest
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import org.springframework.dao.EmptyResultDataAccessException
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import org.springframework.data.util.Version
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import org.springframework.test.context.junit4.SpringRunner
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/**
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* Tests showing Kotlin usage of Spring Data Repositories.
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*
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* @author Mark Paluch
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*/
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@RunWith(SpringRunner::class)
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@SpringBootTest
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class RepositoryTests {
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companion object {
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@JvmField
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@ClassRule
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val CASSANDRA_KEYSPACE = CassandraKeyspace.onLocalhost()
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.atLeast(Version.parse("3.0"))
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}
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@Autowired
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lateinit var repository: PersonRepository
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@Before
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fun before() {
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repository.deleteAll()
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}
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@Test
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fun `should find one person`() {
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repository.save(Person("Walter", "White"))
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val walter = repository.findOneByFirstname("Walter")
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assertThat(walter).isNotNull()
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assertThat(walter.firstname).isEqualTo("Walter")
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assertThat(walter.lastname).isEqualTo("White")
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}
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@Test
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fun `should return null if no person found`() {
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repository.save(Person("Walter", "White"))
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val walter = repository.findOneOrNoneByFirstname("Hank")
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assertThat(walter).isNull()
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}
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@Test
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fun `should throw EmptyResultDataAccessException if no person found`() {
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repository.save(Person("Walter", "White"))
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assertThatThrownBy { repository.findOneByFirstname("Hank") }.isInstanceOf(EmptyResultDataAccessException::class.java)
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}
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}

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