Vaadin-On-Kotlin database mapping library

vok-orm allows you to load the data from database rows into objects (POJOs) and write the data back into the database. No JPA dirty tricks are used: no runtime enhancements, no lazy loading, no DetachedExceptions, no change tracking behind the scenes - everything happens explicitly. No compiler plugin is needed - vok-orm uses Kotlin language features to add a standard set of finders to your entities. You can add any number of business logic methods as you like to your entities; the database transaction is easy to launch simply by calling the global db {} function.

No dependency injection framework is required - the library works in all sorts of environments.

vok-orm uses the jdbi-orm and JDBI under the belt, and introduces first-class Kotlin support on top of those frameworks.

Supported Databases

vok-orm currently supports MySQL, MariaDB, PostgreSQL, H2, Microsoft SQL and CockroachDB. Other databases are untested - they might or might not work.

Usage

Just add the following lines to your Gradle script, to include this library in your project:

repositories {
    mavenCentral()
}
dependencies {
    compile("com.github.mvysny.vokorm:vok-orm:x.y")
}

Note: obtain the newest version from the tag name at the top of the page

Maven: (it's very simple since vok-orm is in Maven Central):

<project>
	<dependencies>
		<dependency>
			<groupId>com.github.mvysny.vokorm</groupId>
			<artifactId>vok-orm</artifactId>
			<version>x.y</version>
		</dependency>
    </dependencies>
</project>

See the vok-orm-playground for a very simple example project using vok-orm.

Compatibility Chart:

vok-orm version	validation API	Min. Java version
1.x	javax.validation	8+
2.x	jakarta.validation	11+

Usage Examples

Say that we have a table containing a list of beverage categories, such as Cider or Beer. The H2 DDL for such table is simple:

create TABLE CATEGORY (
  id bigint auto_increment PRIMARY KEY,
  name varchar(200) NOT NULL
);
create UNIQUE INDEX idx_category_name ON CATEGORY(name);

Note: We expect that the programmer wants to write the DDL scripts herself, to make full use of the DDL capabilities of the underlying database. We will therefore not hide the DDL behind some type-safe generator API.

Such entity can be mapped to a data class as follows:

data class Category(override var id: Long? = null, var name: String = "") : KEntity<Long>

(the id is nullable since its value is initially null until the category is actually created and the id is assigned by the database).

The Category class is just a simple data class: there are no hidden private fields added by runtime enhancements, no hidden lazy loading - everything is pre-fetched upfront. Because of that, the class can be passed around the application freely as a DTO (data transfer object), without the fear of failing with DetachedException when accessing properties. Since Entity is Serializable, you can also store the entity into a session.

The Category class (or any entity class for that matter) must have all fields pre-initialized, so that Kotlin creates a zero-arg constructor. Zero-arg constructor is mandated by JDBI, in order for JDBI to be able to construct instances of entity class for every row returned.

By implementing the KEntity<Long> interface, we are telling vok-orm that the primary key is of type Long; this will be important later on when using Dao. The KEntity interface brings in three useful methods:

• save() which either creates a new row by generating the INSERT statement (if the ID is null), or updates the row by generating the UPDATE statement (if the ID is not null)
• create() for special cases when the ID is pre-known (social security number) and save() wouldn't work. More info in the 'Pre-known IDs' chapter.
• delete() which deletes the row identified by the id primary key from the database.
• validate() validates the bean. By default all javax.validation annotations are validated; you can override this method to provide further bean-level validations. Please read the 'Validation' chapter below, for further details.

There are two interfaces you can use: Entity and KEntity. Both work the same way, however Entity is tailored towards Java developers and is not as pleasant to use with Kotlin as KEntity is.

The INSERT/UPDATE statement is automatically constructed by the save() method, simply by enumerating all non-transient and non-ignored properties of the bean using reflection and fetching their values. See the KEntity sources for more details. You can annotate the Category class with the @Table(dbname = "Categories") annotation, to specify a different table name.

The category can now be created easily:

Category(name = "Beer").save()

But how do we specify the target database where to store the category in?

Connecting to a database

As a bare minimum, you need to specify the JDBC URL and a couple of config parameters as follows:

JdbiOrm.setDataSource(HikariDataSource(HikariConfig()))

to the JdbiOrm.setDataSource() first. It's a Hikari-CP configuration file which contains lots of other options as well. It comes pre-initialized with sensible default settings.

Hikari-CP is a JDBC connection pool which manages a pool of JDBC connections since they are "expensive" to create - it takes some time to establish the TCP-IP connection for example. Typically all projects use some sort of JDBC connection pooling; we'll use Hikari-CP in this tutorial however you can use whichever pool you wish, or no pool at all. You can also use DataSource offered by Spring or JavaEE.

For example, to use an in-memory H2 database, just add H2 onto the classpath as a Gradle dependency: compile 'com.h2database:h2:1.4.196'. Then, configure vok-orm as follows:

val cfg = HikariConfig().apply {
    jdbcUrl = "jdbc:h2:mem:test;DB_CLOSE_DELAY=-1"
    username = "sa"
    password = ""
}
JdbiOrm.setDataSource(HikariDataSource(cfg))

After you have configured the JDBC URL, just call JdbiOrm.setDataSource(HikariDataSource(cfg)) which will initialize Hikari-CP's connection pool. After the connection pool is initialized, you can simply call the db{} function to run the block in a database transaction. The db{} function will acquire new connection from the connection pool; then it will start a transaction and it will provide you with means to execute SQL commands:

db {
    handle.createUpdate("delete from Category where id = :id")
        .bind("id", id)
        .execute()
}

You can call this function from anywhere; you don't need to use dependency injection or anything like that. That is precisely how the save() function saves the bean - it simply calls the db {} function and executes an appropriate INSERT/UPDATE statement.

The function will automatically roll back the transaction on any exception thrown out from the block (both checked and unchecked).

After you're done, call JdbiOrm.destroy() to close the pool.

You can call methods of this library from anywhere. You don't need to be running inside of the JavaEE or Spring container or any container at all - you can actually use this library from a plain JavaSE main method.

Full example of a main() method that does all of the above:

fun main(args: Array<String>) {
    val cfg = HikariConfig().apply {
        jdbcUrl = "jdbc:h2:mem:test;DB_CLOSE_DELAY=-1"
        username = "sa"
        password = ""
    }
    JdbiOrm.setDataSource(HikariDataSource(cfg))
    db {
        con.createQuery("create TABLE CATEGORY (id bigint auto_increment PRIMARY KEY, name varchar(200) NOT NULL );").executeUpdate()
    }
    db {
        (0..100).forEach { Category(name = "cat $it").save() }
    }
    JdbiOrm.destroy()
}

See the vok-orm-playground project which contains such main method, all JDBC drivers pre-loaded and simple instructions on how to query different database kinds.

Note: for the sake of simplicity we're running the CREATE TABLE as a query. For a persistent database it's definitely better to use Flyway as described below.

Finding Categories

The so-called finder (or Dao) methods actually resemble factory methods since they also produce instances of Categories. The best place for such methods is on the Category class itself. We can write all of the necessary finders ourselves, by using the db{} method as stated above; however vok-orm already provides a set of handy methods for you. All you need to do is for the companion object to extend the Dao class:

data class Category(override var id: Long? = null, var name: String = "") : KEntity<Long> {
    companion object : Dao<Category, Long>(Category::class.java)
}

Since Category's companion object extends the Dao class, Category will now be outfitted with several useful finder methods (static extension methods that are attached to the Dao interface itself):

• Category.findAll() will return a list of all categories
• Category.getById(25L) will fetch a category with the ID of 25, failing if there is no such category
• Category.findById(25L) will fetch a category with ID of 25, returning null if there is no such category
• Category.deleteAll() will delete all categories
• Category.deleteById(42L) will delete a category with ID of 42
• Category.count() will return the number of rows in the Category table.
• Category.findBy { "name = :name1 or name = :name2"("name1" to "Beer", "name2" to "Cider") } will find all categories with the name of "Beer" or "Cider". This is an example of a parametrized select, from which you only need to provide the WHERE clause.
• Category.deleteBy { (Category::name eq "Beer") or (Category::name eq "Cider") } will delete all categories matching given criteria. This is an example of a statically-typed matching criteria which is converted into the WHERE clause.
• Category.singleBy { "name = :name"("name" to "Beer") } will fetch exactly one matching category, failing if there is no such category or there are more than one.
• Category.findSingleBy { "name = :name"("name" to "Beer") } will fetch one matching category, failing if there are more than one. Returns null if there is none.
• Category.count { "name = :name"("name" to "Beer") } will return the number of rows in the Category table matching given query.

In the spirit of type safety, the finder methods will only accept Long (or whatever is the type of the primary key in the KEntity<x> implementation clause).

You can of course add your own custom finder methods into the Category companion object. For example:

data class Category(override var id: Long? = null, var name: String = "") : KEntity<Long> {
    companion object : Dao<Category> {
        fun findByName(name: String): Category? = findSingleBy { Category::name eq name }
        fun getByName(name: String): Category = singleBy { Category::name eq name }
        fun existsWithName(name: String): Boolean = count { Category::name eq name } > 0
    }
}

Note: If you don't want to use the KEntity interface for some reason (for example when the table has no primary key), you can still include useful finder methods by making the companion object to implement the DaoOfAny interface. The finder methods such as findById() will accept Any as a primary key.

Adding Reviews

Let's add the second table, the "Review" table. The Review table is a list of reviews for various drinks; it back-references the drink category as a foreign key into the Category table:

create TABLE REVIEW (
  id bigint auto_increment PRIMARY KEY,
  beverageName VARCHAR(200) not null,
  score TINYINT NOT NULL,
  date DATE not NULL,
  category BIGINT,
  count TINYINT not null
);
alter table Review add CONSTRAINT r_score_range CHECK (score >= 1 and score <= 5);
alter table Review add FOREIGN KEY (category) REFERENCES Category(ID);
alter table Review add CONSTRAINT r_count_range CHECK (count >= 1 and count <= 99);
create INDEX idx_beverage_name ON Review(beverageName);

The mapping class is as follows:

/**
 * Represents a beverage review.
 * @property score the score, 1..5, 1 being worst, 5 being best
 * @property date when the review was done
 * @property category the beverage category [Category.id]
 * @property count times tasted, 1..99
 */
data class Review(override var id: Long? = null,
                  var score: Int = 1,
                  var beverageName: String = "",
                  var date: LocalDate = LocalDate.now(),
                  var category: Long? = null,
                  var count: Int = 1) : KEntity<Long> {

    companion object : Dao<Review, Long>(Review::class.java)
}

Now if we want to delete a category, we need to first set the Review.category value to null for all reviews that are linked to that very category, otherwise we will get a foreign constraint violation. It's quite easy: just override the delete() method in the Category class as follows:

data class Category(/*...*/) : KEntity<Long> {
    // ...
    override fun delete() {
        db {
            if (id != null) {
                handle.createQuery("update Review set category = NULL where category=:catId")
                        .bind("catId", id!!)
                        .executeUpdate()
            }
            super.delete()
        }
    }
}

Note: for all slightly more complex queries it's a good practice to simply use the JDBI API - we will simply pass in the SQL command as a String to JDBI.

As you can see, you can use the JDBI connection yourself, to execute any kind of SELECT/UPDATE/INSERT/DELETE statements as you like. For example you can define static finder or computation method into the Review companion object:

    companion object : Dao<Review, Long>(Review::class.java) {
        /**
         * Computes the total sum of [count] for all reviews belonging to given [categoryId].
         * @return the total sum, 0 or greater.
         */
        fun getTotalCountForReviewsInCategory(categoryId: Long): Long = db {
            handle.createQuery("select sum(r.count) from Review r where r.category = :catId")
                    .bind("catId", categoryId)
                    .mapTo(Long::class.java).one() ?: 0L
        }
    }

Then we can outfit the Category itself with this functionality, by adding an extension method to compute this value:

fun Category.getTotalCountForReviews(): Long = Review.getTotalCountForReviewsInCategory(id!!)

Note how freely and simply we can add useful business logic methods to entities. It's because:

• the entities are just plain old classes with no hidden fields and no runtime enhancements, and
• because we can invoke db{} freely from anywhere. You don't need transaction annotations and injected entity managers, and you don't need huge container such as Spring or JavaEE which must instantiate your classes in order to activate those annotations and injections. Those are things of the past.

Auto-generated IDs vs pre-provided IDs

There are generally three cases for entity ID generation:

• IDs generated by the database when the INSERT statement is executed
• Natural IDs, such as a NaturalPerson with ID pre-provided by the government (social security number etc).
• IDs created by the application, for example via UUID.randomUUID()

The save() method is designed to work out-of-the-box only for the first case (IDs auto-generated by the database). In this case, save() emits INSERT when the ID is null, and UPDATE when the ID is not null.

When the ID is pre-provided, you can only use save() method to update a row in the database; using save() to create a row in the database will throw an exception. In order to create an entity with a pre-provided ID, you need to use the create() method:

NaturalPerson(id = "12345678", name = "Albedo").create()

For entities with IDs created by the application you can make save() work properly, by overriding the create() method in your entity as follows:

override fun create(validate: Boolean) {
  id = UUID.randomUUID()
  super.create(validate)
}

Even better, you can inherit from the Entity interface as follows:

interface UuidEntity : KEntity<UUID> {
    override fun create(validate: Boolean) {
        id = UUID.randomUUID()
        super.create(validate)
    }
}

And simply make all of your entities implement the UuidEntity interface.

Joins

When we display a list of reviews (say, in a Vaadin Grid), we want to display an actual category name instead of the numeric category ID. We can take advantage of JDBI simply matching all SELECT column names into bean fields; all we have to do is to:

• create a new class which contains both the Review field and add the categoryName field which will carry the category name information;
• write a SELECT that will return all of the Review fields, and, additionally, the categoryName field

Let's thus create a ReviewWithCategory class:

class ReviewWithCategory : Serializable {
    @field:Nested
    var review: Review = Review()
    @field:ColumnName("categoryName")
    var categoryName: String? = null
}

Note the @ColumnName annotation which tells vok-orm that the field is named differently in the database. Often the database naming schema is different from Kotlin's naming schema, for example NUMBER_OF_PETS would be represented by the numberOfPets in the Kotlin class. You can use database aliases, for example SELECT NUMBER_OF_PETS AS numberOfPets. However note that you can't then add a WHERE clause on the numberOfPets alias - that's not supported by SQL databases. See Issue #5 for more details. Currently we don't use WHERE in our examples so you're free to use aliases, but aliases do not work with Data Loaders and therefore it's a good practice to use @ColumnName instead of SQL aliases.

Now we can add a new finder function into ReviewWithCategory's companion object:

companion object : DaoOfAny<ReviewWithCategory>(ReviewWithCategory::class.java) {
    //...
    fun findReviews(): List<ReviewWithCategory> = db {
        handle.createQuery("""select r.*, c.name
            FROM Review r left join Category c on r.category = c.id
            ORDER BY r.name""")
                .map(getRowMapper())
                .list()
    }
}

It also makes sense to add this function to Review's companion object:

companion object : Dao<Review>(Review::class.java) {
    //...
    fun findReviews() = ReviewWithCategory.findReviews()
}

We can take JDBI's mapping capabilities to full use: we can craft any SELECT we want, and then we can create a holder class that will not be an entity itself, but will merely hold the result of that SELECT. The only thing that matters is that the class will have properties named exactly as the columns in the SELECT statement (or properly aliased using the @ColumnName annotation):

data class Beverage(@field:ColumnName("beverageName") var name: String = "", @field:ColumnName("name") var category: String? = null) : Serializable {
    companion object {
        fun findAll(): List<Beverage> = db {
            handle.createQuery("select r.beverageName, c.name from Review r left join Category c on r.category = c.id")
                .map(FieldMapper.of(Beverage::class.java))
                .list()
        }
    }
}

We just have to make sure that all of the Beverage's fields are pre-initialized, so that the Beverage class has a zero-arg constructor. If not, JDBI will throw an exception in runtime, stating that the Beverage class has no zero-arg constructor.

Validations

Often the database entities are connected to UI forms which need to provide sensible validation errors to the users as they enter invalid values. The validation could be done on the database level, but databases tend to provide unlocalized cryptic error messages. Also, some validations are either impossible to do, or very hard to do on the database level. That's why vok-orm provides additional validation layer for your entities.

vok-orm uses JSR303 Java Standard for Validation; you can quickly skim over JSR303 tutorial to see how to start using the validation. In a nutshell, you annotate your KEntity's fields with validation annotations; the fields are then checked for valid values with the JSR303 Validator (invoked when entity.validate()/entity.save()/entity.create() is called). The validation is also mentioned in Vaadin-on-Kotlin Forms documentation.

For example:

data class Person(
        override var id: Long? = null,

        @field:NotNull
        @field:Size(min = 1, max = 200)
        var name: String? = null,

        @field:NotNull
        @field:Min(15)
        @field:Max(100)
        var age: Int? = null) : KEntity<Long>
val p = Person(name = "John", age = 10)
p.validate() // throws an exception since age must be at least 15

Important note: the validation is an optional feature in vok-orm, and by default the validation is disabled. This fact is advertised in the vok-orm logs as the following message:

JSR 303 Validator Provider was not found on your classpath, disabling entity validation

In order to activate the entity validations, you need to add a JSR303 Validation Provider jar to your classpath. Just use Hibernate-Validator (don't worry it will not pull in Hibernate nor JPA) and add this to your build.gradle:

dependencies {
  compile("org.hibernate.validator:hibernate-validator:6.0.17.Final")
  // EL is required: http://hibernate.org/validator/documentation/getting-started/
  compile("org.glassfish:javax.el:3.0.1-b08")
}

You can check out the vok-orm-playground which has validations enabled and all necessary jars included.

Data Loaders

The support for Data Loader is deprecated and removed.

Vaadin

For Vaadin integration please see jdbi-orm-vaadin which supports vok-orm too, and it provides support for all sorts of data providers including entity, POJO and joins/custom SQL statements.

For Vaadin example apps, please take a look at:

• beverage-buddy-vok: A full-blown Vaadin Kotlin app which demoes vok-orm-based CRUD
• vok-security-demo: uses vok-orm to load users
• vaadin-kotlin-pwa: demoes Vaadin+Kotlin+CRUD as well

Full-Text Filters

In order for the FullTextFilter filter to work, you must create a proper full-text index in your database for the column being matched. Please see the documentation for individual databases below.

To customize the SQL scripts being generated, you can create a delegate FilterToSqlConverter which is able to handle FullTextFilters and passes through all other filters to the default VokOrm.filterToSqlConverter.

The FullTextFilter class cleans up the user input, removes any non-alphabetic and non-digit characters and turns user input into a set of words. The words will never contain characters such as + / * which are often used by the full text engine. Therefore, it's easy to join the words and produce a full-text query.

In order for the Filter converter to know which syntax to produce, you must set your database variant in VokOrm.databaseVariant. The default one is 'Unknown' and since there is no full-text matching in SQL92, by default all FullTextFilter conversion will fail.

H2

Full-Text searches are supported. vok-orm uses FullTextLucene implementation since the native H2 implementation can't do partial matches (e.g. filter car won't match carousel).

The following WHERE clauses are produced by default:

$idColumn IN (SELECT CAST(FT.KEYS[1] AS BIGINT) AS ID FROM FTL_SEARCH_DATA(:$parameterName, 0, 0) FT WHERE FT.`TABLE`='${meta.databaseTableName.toUpperCase()}')

You need to call the following to init the engine and create the index:

CREATE ALIAS IF NOT EXISTS FTL_INIT FOR "org.h2.fulltext.FullTextLucene.init";
CALL FTL_INIT();
CALL FTL_CREATE_INDEX('PUBLIC', 'TEST', 'NAME');  -- Adds index on the 'NAME' column of the 'TEST' table.

Make sure to use upper-case table+column names otherwise H2 will complain that the column/table doesn't exist.

You will need to add Lucene on the classpath:

    compile("org.apache.lucene:lucene-analyzers-common:5.5.5")
    compile("org.apache.lucene:lucene-queryparser:5.5.5")

Limitations:

• Only tables with non-composite BIGINT primary keys are supported. You can lift this limitation by implementing your own FilterToSqlConverter and constructing your own query.

See H2 Full-Text search for more info.

PostgreSQL

The following WHERE clauses are produced by default: to_tsvector('english', $databaseColumnName) @@ to_tsquery('english', 'fat:* cat:*').

A full-text index is not necessary in order for PostgreSQL to properly match records, however the performance will be horrible. I recommend to create the index, e.g. CREATE INDEX pgweb_idx ON Test USING GIN (to_tsvector('english', name)).

See PostgreSQL Full-Text search for more info.

MySQL/MariaDB

You'll need to create a FULLTEXT index for the column, otherwise MySQL will match nothing.

By default the following WHERE clauses are produced: e.g. when searching for "fat cat", this is emitted: MATCH($databaseColumnName) AGAINST ("+fat* +cat*" IN BOOLEAN MODE).

MySQL has a number of quirks to look after:

• Sometimes MySQL will use another index instead of a full-text index: MySQL sporadic MATCH AGAINST behaviour with unique index Either delete the offending index, or use [NativeFilter] and IGNORE INDEX ()

Why the filter is using BOOLEAN mode instead of NATURAL LANGUAGE mode:

• Random treating of words as stopwords because they're present in more than 50% of the rows: MySQL Natural Language.
• No way to match word beginnings.

Aliases

Often database columns follow different naming convention than bean fields, e.g. database CUSTOMER_NAME should be mapped to the CustomerAddress::customerName field. The first thing to try is to use aliases in the SQL itself, for example

select c.CUSTOMER_NAME as customerName from Customer c ...;

The problem with this approach is twofold:

• Databases can't sort nor filter based on aliased column; please see Issue 5 for more details. Using such queries with SqlDataLoader and trying to pass in filter such as buildFilter<CustomerAddress> { "customerName ILIKE cn"("cn" to "Foo%") } will cause the select command to fail with SqlException.
• INSERTs/UPDATEs issued by your entity Dao will fail since they will use the bean field names instead of actual column name and will emit INSERT INTO Customer (customerName) values ($1) instead of INSERT INTO Customer (CUSTOMER_NAME) values ($1)

Therefore, instead of database-based aliases it's better to use the @ColumnName annotation on your beans, both natural entities such as Customer and projection-only entities such as CustomerAddress:

data class Customer(@field:ColumnName("CUSTOMER_NAME") var name: String? = null) : KEntity<Long>
data class CustomerAddress(@field:ColumnName("CUSTOMER_NAME") var customerName: String? = null)

The @ColumnName annotation is honored both by Daos and by all data loaders.

A main() method Example

Using the vok-orm library from a JavaSE main method; see the vok-orm-playground for a very simple example project using vok-orm.

data class Person(
    override var id: Long? = null,
    var name: String = "",
    var age: Int = 0,
    var dateOfBirth: LocalDate? = null,
    var recordCreatedAt: Instant? = null
) : KEntity<Long> {
    override fun save(validate: Boolean) {
        if (id == null) {
            recordCreatedAt = Instant.now()
        }
        super.save(validate)
    }

    companion object : Dao<Person, Long>(Person::class.java)
}

fun main(args: Array<String>) {
    val cfg = HikariConfig().apply {
        jdbcUrl = "jdbc:h2:mem:test;DB_CLOSE_DELAY=-1"
    }
    JdbiOrm.setDataSource(HikariDataSource(cfg))
    db {
        con.createQuery(
            """create table if not exists Test (
            id bigint primary key auto_increment,
            name varchar not null,
            age integer not null,
            dateOfBirth date,
            recordCreatedAt timestamp
             )"""
        ).executeUpdate()
    }
    
    // runs SELECT * FROM Person
    // prints []
    println(Person.findAll())
    
    // runs INSERT INTO Person (name, age, recordCreatedAt) values (:p1, :p2, :p3)
    Person(name = "John", age = 42).save()
    
    // runs SELECT * FROM Person
    // prints [Person(id=1, name=John, age=42, dateOfBirth=null, recordCreatedAt=2011-12-03T10:15:30Z)]
    println(Person.findAll())
    
    // runs SELECT * FROM Person where id=:id
    // prints John
    println(Person.getById(1L).name)
    
    // mass-saves 11 persons in a single transaction.
    db { (0..10).forEach { Person(name = "person $it", age = it).save() } }
    
    JdbiOrm.destroy()
}

Using Flyway to migrate the database

Flyway is able to run DDL scripts on given database and track which scripts already ran. This way, you can simply add more scripts and Flyway will apply them, to migrate the database to the newest version. This even works in a cluster since Flyway will obtain a database lock, locking out other members of the cluster attempting to upgrade.

Let's use the Category example from above. We need Flyway to run two scripts, to initialize the database: one creates the table, while other creates the indices.

You don't need to use Flyway plugin. Just add the following Gradle dependency to your project:

compile "org.flywaydb:flyway-core:6.0.7"

Flyway expects the migration scripts named in a certain format, to know the order in which to execute them. Create the db.migration package in your src/main/resources and put two files there: the V01__CreateCategory.sql file:

create TABLE CATEGORY (
  id bigint auto_increment PRIMARY KEY,
  name varchar(200) NOT NULL
);

The next one will be V02__CreateIndexCategoryName.sql:

create UNIQUE INDEX idx_category_name ON CATEGORY(name);

In order to run the migrations, just run the following after JdbiOrm.setDataSource():

val flyway = Flyway()
flyway.dataSource = JdbiOrm.getDataSource()
flyway.migrate()

Using with Spring or JavaEE

By default VoK-ORM connects to the JDBC database directly and uses its own instance of Hikari-CP to pool JDBC connections. That of course doesn't work with containers such as Spring or JavaEE which manage JDBC resources themselves.

It is very easy to use VoK-ORM with Spring or JavaEE. All you need is to obtain an instance of DataSource when your server boots up, then simply set it to JdbiOrm via JdbiOrm.setDataSource(). VoK-ORM will then simply poll Spring or JavaEE DataSource for connections; Spring/JavaEE will then make sure the connections are pooled properly.

You don't even need to call JdbiOrm.destroy() on Spring/JavaEE app shutdown: all JdbiOrm.destroy() does is that it closes the DataSource, however Spring/JavaEE will do that for us.

vok-orm design principles

vok-orm is a very simple object-relational mapping library, built around the following ideas:

• Simplicity is the most valued property; working with plain SQL commands is preferred over having a type-safe query language. If you want a type-safe database mapping library, try Exposed.
• The database is the source of truth. JVM objects are nothing more than DTOs, merely capture snapshots of the JDBC ResultSet rows. The entities are populated by the means of reflection: for every column in the JDBC ResultSet an appropriate setter is invoked, to populate the data.
• The entities are real POJOs: they do not track modifications, they do not automatically store modified values back into the database. They are not runtime-enhanced and can be final.
• A switch from one type of database to another never happens. We understand that the programmer wants to exploit the full potential of the database, by writing SQLs tailored for that particular database. vok-orm should not attempt to generate SELECTs on behalf of the programmer (except for the very basic ones related to CRUD); instead it should simply allow SELECTs to be passed as Strings, and then map the result to an object of programmer's choosing.

As such, vok-orm has much in common with the ActiveJDBC project, in terms of design principles. The advantage of vok-orm is that it doesn't require any instrumentation to work (instead it uses Kotlin language features), and it's even simpler than ActiveJDBC.

Please read Back to Base - make SQL great again for the complete explanation of ideas behind this framework.

This framework uses JDBI to map data from the JDBC ResultSet to POJOs; in addition it provides a very simple mechanism to store/update the data back to the database.

Comparison with other database-related libraries

• ActiveJDBC has much in common with jdbi-orm; the advantage of jdbi-orm is that we do not require any instrumentation to work (we use only Java language features).
• JOOQ is great but requires initial generation of java code from your database scheme (you write your entities by hand with jdbi-orm), and promotes type-safe query building instead of plain SQLs. There's the usual set of problems coming with generated classes: you can't add your custom utility functions to those, you can't add validation annotations, etc. If you don't mind that, go for JOOQ - it's definitely more popular than jdbi-orm.
• JPA: just no. We want real POJOs, not a dynamically-enhanced thing managed by the Entity Manager. Also see below.
• Spring JdbcTemplate: not bad but it depends on Spring; jdbi-orm must be able to work on pure JVM, without Spring.

Why not JPA

JPA promises simplicity of usage by providing an object-oriented API. However, this is achieved by creating a virtual object database layer over a relational database; that creates much complexity under the hood which leaks in various ways. In short, JPA is a double failure: it chose the wrong abstraction, and implemented it poorly.

There are major issues in JPA which cannot be overlooked:

• Vaadin-on-Kotlin Issue #3 Remove JPA
• Back to Base - make SQL great again
• Do-It-Yourself ORM as an Alternative to Hibernate

We strive to erase the virtual object database layer. We acknowledge the existence of the relational database; we only provide tools to ease the use of the database from a statically-typed OOP language.

Running tests

Running ./gradlew or ./gradlew test will run all tests on all databases (given that Docker is available on the host system). To run the tests on H2 only (the test suite will run much faster), run with ./gradlew -Dh2only=true

License

Licensed under the MIT License.

Copyright (c) 2017-2018 Martin Vysny

All rights reserved.

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.