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Merge pull request #1563 from manannikov/Issue#1284

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#1284 Implement Version Number pattern
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Ilkka Seppälä 2020-11-23 22:35:43 +02:00 committed by GitHub
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pom.xml
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<module>state</module> <module>state</module>
<module>strategy</module> <module>strategy</module>
<module>template-method</module> <module>template-method</module>
<module>version-number</module>
<module>visitor</module> <module>visitor</module>
<module>double-checked-locking</module> <module>double-checked-locking</module>
<module>servant</module> <module>servant</module>

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---
layout: pattern
title: Version Number
folder: versionnumber
permalink: /patterns/versionnumber/
description: Entity versioning with version number
categories:
- Concurrency
tags:
- Data access
- Microservices
---
## Name / classification
Version Number.
## Also known as
Entity Versioning, Optimistic Locking.
## Intent
Resolve concurrency conflicts when multiple clients are trying to update same entity simultaneously.
## Explanation
Real world example
> Alice and Bob are working on the book, which stored in the database. Our heroes are making
> changes simultaneously, and we need some mechanism to prevent them from overwriting each other.
In plain words
> Version Number pattern grants protection against concurrent updates to same entity.
Wikipedia says
> Optimistic concurrency control assumes that multiple transactions can frequently complete
> without interfering with each other. While running, transactions use data resources without
> acquiring locks on those resources. Before committing, each transaction verifies that no other
> transaction has modified the data it has read. If the check reveals conflicting modifications,
> the committing transaction rolls back and can be restarted.
**Programmatic Example**
We have a `Book` entity, which is versioned, and has a copy-constructor:
```java
public class Book {
private long id;
private String title = "";
private String author = "";
private long version = 0; // version number
public Book(Book book) {
this.id = book.id;
this.title = book.title;
this.author = book.author;
this.version = book.version;
}
// getters and setters are omitted here
}
```
We also have `BookRepository`, which implements concurrency control:
```java
public class BookRepository {
private final Map<Long, Book> collection = new HashMap<>();
public void update(Book book) throws BookNotFoundException, VersionMismatchException {
if (!collection.containsKey(book.getId())) {
throw new BookNotFoundException("Not found book with id: " + book.getId());
}
var latestBook = collection.get(book.getId());
if (book.getVersion() != latestBook.getVersion()) {
throw new VersionMismatchException(
"Tried to update stale version " + book.getVersion()
+ " while actual version is " + latestBook.getVersion()
);
}
// update version, including client representation - modify by reference here
book.setVersion(book.getVersion() + 1);
// save book copy to repository
collection.put(book.getId(), new Book(book));
}
public Book get(long bookId) throws BookNotFoundException {
if (!collection.containsKey(bookId)) {
throw new BookNotFoundException("Not found book with id: " + bookId);
}
// return copy of the book
return new Book(collection.get(bookId));
}
}
```
Here's the concurrency control in action:
```java
var bookId = 1;
// Alice and Bob took the book concurrently
final var aliceBook = bookRepository.get(bookId);
final var bobBook = bookRepository.get(bookId);
aliceBook.setTitle("Kama Sutra"); // Alice has updated book title
bookRepository.update(aliceBook); // and successfully saved book in database
LOGGER.info("Alice updates the book with new version {}", aliceBook.getVersion());
// now Bob has the stale version of the book with empty title and version = 0
// while actual book in database has filled title and version = 1
bobBook.setAuthor("Vatsyayana Mallanaga"); // Bob updates the author
try {
LOGGER.info("Bob tries to update the book with his version {}", bobBook.getVersion());
bookRepository.update(bobBook); // Bob tries to save his book to database
} catch (VersionMismatchException e) {
// Bob update fails, and book in repository remained untouchable
LOGGER.info("Exception: {}", e.getMessage());
// Now Bob should reread actual book from repository, do his changes again and save again
}
```
Program output:
```java
Alice updates the book with new version 1
Bob tries to update the book with his version 0
Exception: Tried to update stale version 0 while actual version is 1
```
## Class diagram
![alt text](etc/version-number.urm.png "Version Number pattern class diagram")
## Applicability
Use Version Number for:
* resolving concurrent write-access to the data
* strong data consistency
## Tutorials
* [Version Number Pattern Tutorial](http://www.java2s.com/Tutorial/Java/0355__JPA/VersioningEntity.htm)
## Known uses
* [Hibernate](https://vladmihalcea.com/jpa-entity-version-property-hibernate/)
* [Elasticsearch](https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-index_.html#index-versioning)
* [Apache Solr](https://lucene.apache.org/solr/guide/6_6/updating-parts-of-documents.html)
## Consequences
Version Number pattern allows to implement a concurrency control, which is usually done
via Optimistic Offline Lock pattern.
## Related patterns
* [Optimistic Offline Lock](https://martinfowler.com/eaaCatalog/optimisticOfflineLock.html)
## Credits
* [Optimistic Locking in JPA](https://www.baeldung.com/jpa-optimistic-locking)
* [JPA entity versioning](https://www.byteslounge.com/tutorials/jpa-entity-versioning-version-and-optimistic-locking)
* [J2EE Design Patterns](http://ommolketab.ir/aaf-lib/axkwht7wxrhvgs2aqkxse8hihyu9zv.pdf)

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@startuml
package com.iluwatar.versionnumber {
class App {
- LOGGER : Logger {static}
+ App()
+ main(args : String[]) {static}
}
class Book {
- author : String
- id : long
- title : String
- version : long
+ Book()
+ Book(book : Book)
+ getAuthor() : String
+ getId() : long
+ getTitle() : String
+ getVersion() : long
+ setAuthor(author : String)
+ setId(id : long)
+ setTitle(title : String)
+ setVersion(version : long)
}
class BookRepository {
- collection : Map<Long, Book>
+ BookRepository()
+ add(book : Book)
+ get(bookId : long) : Book
+ update(book : Book)
}
}
@enduml

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<?xml version="1.0"?>
<!--
The MIT License
Copyright © 2014-2019 Ilkka Seppälä
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
-->
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>com.iluwatar</groupId>
<artifactId>java-design-patterns</artifactId>
<version>1.24.0-SNAPSHOT</version>
</parent>
<artifactId>version-number</artifactId>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-core</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<executions>
<execution>
<configuration>
<archive>
<manifest>
<mainClass>com.iluwatar.versionnumber.App</mainClass>
</manifest>
</archive>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.versionnumber;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* The Version Number pattern helps to resolve concurrency conflicts in applications.
* Usually these conflicts arise in database operations, when multiple clients are trying
* to update the same record simultaneously.
* Resolving such conflicts requires determining whether an object has changed.
* For this reason we need a version number that is incremented with each change
* to the underlying data, e.g. database. The version number can be used by repositories
* to check for external changes and to report concurrency issues to the users.
*
* <p>In this example we show how Alice and Bob will try to update the {@link Book}
* and save it simultaneously to {@link BookRepository}, which represents a typical database.
*
* <p>As in real databases, each client operates with copy of the data instead of original data
* passed by reference, that's why we are using {@link Book} copy-constructor here.
*/
public class App {
private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
/**
* Program entry point.
*
* @param args command line args
*/
public static void main(String[] args) throws
BookDuplicateException,
BookNotFoundException,
VersionMismatchException {
var bookId = 1;
var bookRepository = new BookRepository();
var book = new Book();
book.setId(bookId);
bookRepository.add(book); // adding a book with empty title and author
LOGGER.info("An empty book with version {} was added to repository", book.getVersion());
// Alice and Bob took the book concurrently
final var aliceBook = bookRepository.get(bookId);
final var bobBook = bookRepository.get(bookId);
aliceBook.setTitle("Kama Sutra"); // Alice has updated book title
bookRepository.update(aliceBook); // and successfully saved book in database
LOGGER.info("Alice updates the book with new version {}", aliceBook.getVersion());
// now Bob has the stale version of the book with empty title and version = 0
// while actual book in database has filled title and version = 1
bobBook.setAuthor("Vatsyayana Mallanaga"); // Bob updates the author
try {
LOGGER.info("Bob tries to update the book with his version {}", bobBook.getVersion());
bookRepository.update(bobBook); // Bob tries to save his book to database
} catch (VersionMismatchException e) {
// Bob update fails, and book in repository remained untouchable
LOGGER.info("Exception: {}", e.getMessage());
// Now Bob should reread actual book from repository, do his changes again and save again
}
}
}

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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.versionnumber;
public class Book {
private long id;
private String title = "";
private String author = "";
private long version = 0; // version number
public Book() {
}
/**
* We need this copy constructor to copy book representation in {@link BookRepository}.
*/
public Book(Book book) {
this.id = book.id;
this.title = book.title;
this.author = book.author;
this.version = book.version;
}
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public long getVersion() {
return version;
}
public void setVersion(long version) {
this.version = version;
}
}

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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.versionnumber;
/**
* When someone has tried to add a book which repository already have.
*/
public class BookDuplicateException extends Exception {
public BookDuplicateException(String message) {
super(message);
}
}

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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.versionnumber;
/**
* Client has tried to make an operation with book which repository does not have.
*/
public class BookNotFoundException extends Exception {
public BookNotFoundException(String message) {
super(message);
}
}

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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.versionnumber;
import java.util.HashMap;
import java.util.Map;
/**
* This repository represents simplified database.
* As a typical database do, repository operates with copies of object.
* So client and repo has different copies of book, which can lead to concurrency conflicts
* as much as in real databases.
*/
public class BookRepository {
private final Map<Long, Book> collection = new HashMap<>();
/**
* Adds book to collection.
* Actually we are putting copy of book (saving a book by value, not by reference);
*/
public void add(Book book) throws BookDuplicateException {
if (collection.containsKey(book.getId())) {
throw new BookDuplicateException("Duplicated book with id: " + book.getId());
}
// add copy of the book
collection.put(book.getId(), new Book(book));
}
/**
* Updates book in collection only if client has modified the latest version of the book.
*/
public void update(Book book) throws BookNotFoundException, VersionMismatchException {
if (!collection.containsKey(book.getId())) {
throw new BookNotFoundException("Not found book with id: " + book.getId());
}
var latestBook = collection.get(book.getId());
if (book.getVersion() != latestBook.getVersion()) {
throw new VersionMismatchException(
"Tried to update stale version " + book.getVersion()
+ " while actual version is " + latestBook.getVersion()
);
}
// update version, including client representation - modify by reference here
book.setVersion(book.getVersion() + 1);
// save book copy to repository
collection.put(book.getId(), new Book(book));
}
/**
* Returns book representation to the client.
* Representation means we are returning copy of the book.
*/
public Book get(long bookId) throws BookNotFoundException {
if (!collection.containsKey(bookId)) {
throw new BookNotFoundException("Not found book with id: " + bookId);
}
// return copy of the book
return new Book(collection.get(bookId));
}
}

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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.versionnumber;
/**
* Client has tried to update a stale version of the book.
*/
public class VersionMismatchException extends Exception {
public VersionMismatchException(String message) {
super(message);
}
}

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version-number/src/test/java/com/iluwatar/versionnumber/AppTest.java Normal file
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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.versionnumber;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
/**
* Application test
*/
class AppTest {
/**
* Issue: Add at least one assertion to this test case.
*
* Solution: Inserted assertion to check whether the execution of the main method in {@link App#main(String[])}
* throws an exception.
*/
@Test
void shouldExecuteApplicationWithoutException() {
assertDoesNotThrow(() -> App.main(new String[]{}));
}
}

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/*
* The MIT License
* Copyright © 2014-2019 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.versionnumber;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;
/**
* Tests for {@link BookRepository}
*/
class BookRepositoryTest {
private final long bookId = 1;
private final BookRepository bookRepository = new BookRepository();
@BeforeEach
public void setUp() throws BookDuplicateException {
var book = new Book();
book.setId(bookId);
bookRepository.add(book);
}
@Test
void testDefaultVersionRemainsZeroAfterAdd() throws BookNotFoundException {
var book = bookRepository.get(bookId);
assertEquals(0, book.getVersion());
}
@Test
void testAliceAndBobHaveDifferentVersionsAfterAliceUpdate() throws BookNotFoundException, VersionMismatchException {
final var aliceBook = bookRepository.get(bookId);
final var bobBook = bookRepository.get(bookId);
aliceBook.setTitle("Kama Sutra");
bookRepository.update(aliceBook);
assertEquals(1, aliceBook.getVersion());
assertEquals(0, bobBook.getVersion());
var actualBook = bookRepository.get(bookId);
assertEquals(aliceBook.getVersion(), actualBook.getVersion());
assertEquals(aliceBook.getTitle(), actualBook.getTitle());
assertNotEquals(aliceBook.getTitle(), bobBook.getTitle());
}
@Test
void testShouldThrowVersionMismatchExceptionOnStaleUpdate() throws BookNotFoundException, VersionMismatchException {
final var aliceBook = bookRepository.get(bookId);
final var bobBook = bookRepository.get(bookId);
aliceBook.setTitle("Kama Sutra");
bookRepository.update(aliceBook);
bobBook.setAuthor("Vatsyayana Mallanaga");
try {
bookRepository.update(bobBook);
} catch (VersionMismatchException e) {
assertEquals(0, bobBook.getVersion());
var actualBook = bookRepository.get(bookId);
assertEquals(1, actualBook.getVersion());
assertEquals(aliceBook.getVersion(), actualBook.getVersion());
assertEquals("", bobBook.getTitle());
assertNotEquals(aliceBook.getAuthor(), bobBook.getAuthor());
}
}
}