Folo

Successor to Jolo, a jOOQ Loader. Folo is a utility library to add basic object-relation mapping to your jOOQ code.

Features

• Easy specification of relations between entities using a chaining API.
• Implements java.util.stream.Collector allowing object instantiation using jOOQ's native ResultQuery#collect method; the loader can additionally call setters to instantiate relationships between entities.
• Performs foreign key checks to see whether the defined relationships make sense.
• Extra checks on field names of returned records to prevent loading fields from one table as fields of another (no implicit conversion of FOO.FIELD to BAR.FIELD).
• Supports circular references.
• Supports adding extra (non-table) fields to entities.

Example usage

Let's assume we are working with the following table structure:

CREATE TABLE Dog
(
    id     bigserial PRIMARY KEY,
    name   text,
    weight int
);

CREATE TABLE Flea
(
    id     bigserial PRIMARY KEY,
    dog_id bigint REFERENCES Dog,
    weight int
)

And in Java you have modelled your dogs and fleas using POJOs that are serialisable using standard jOOQ functionality:

class Dog {
    private long id;
    private String name;
    private int weight;
    private List<Flea> fleas;

    /* Getters and setters for ID, name & weight. */

    @Transient
    public List<Flea> getFleas() {
        return fleas;
    }

    public void setFleas(List<Flea> fleas) {
        this.fleas = fleas;
    }
}

class Flea {
    private long id;
    private int weight;

    /* Getters and setters. */
}

Using this library, you can specify how to instantiate the relationship between those POJOs (i.e., how to fill the fleas property of Dog):

class LoaderUtil {
    static Loader<Dog> createLoader() {
        var dog = new Entity<>(Tables.DOG, Dog.class);
        var flea = new Entity<>(Tables.FLEA, Flea.class);
        return Loader.of(dog).oneToMany(dog, flea).setManyLeft(Dog::setFleas).build();
    }
}

Then in the code that executes the query, you can use the loader to instantiate and link POJO classes:

class Repository {
    private static final Loader<Dog> LOADER = createLoader();

    private final DSLContext context;

    void dogLog() {
        List<Dog> dogs = context.select()
                .from(DOG)
                .leftJoin(FLEA)
                .on(FLEA.DOG_ID.eq(DOG.ID))
                .collect(toLinkedObjectsWith(LOADER));

        for (Dog dog : dogs) {
            int fleaWeight = dog.getFleas().stream().mapToInt(Flea::getWeight).sum();
            LOG.info("%s is %.0f%% fleas",
                    dog.getName(),
                    fleaWeight * 100.0 / dog.getWeight());
        }
    }
}

How to Install

Artifacts are hosted on Maven's Central Repository:

Gradle

dependencies {
    compile 'io.github.ferdinand-swoboda.folo:folo:2.0.0'
}

Maven

<dependency>
    <groupId>io.github.ferdinand-swoboda.folo</groupId>
    <artifactId>folo</artifactId>
    <version>2.0.0</version>
</dependency>

Limitations/Potential improvements

• Make use of Java modules (introduced in Java 9).
• Only primary / foreign keys of (Java) type long are supported i.e. no composite or UUID keys.
• Investigate nullness annotations (e.g. javax.annotations, org.jspecify).
• Investigate @Contract annotations (org.jetbrains).
• Relation mapping does not work for entities that are not based on a table in the DB schema.

Contributing

Contributions of any kind are welcome! Feel free to file an issue or open a pull request.

When submitting changes, please make every effort to follow existing conventions and style in order to keep the code as readable as possible. New code must be covered by tests. As a rule of thumb, overall test coverage should not decrease, performance metrics should stay the same or improve.