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Happy Programmer Day!

Boris Kirzner — Sun, 13 Sep 2009 07:09:21 +0000

Russia’s New Official Holiday — Programmer’s Day

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JTL goes open-source

Boris Kirzner — Sat, 06 Sep 2008 19:23:10 +0000

JTL, the Java Tools Language (pronounced “Gee-tel”), is a high-level query language for selecting program elements, designed to serve the development of source code software tools for Java.
It is both simple and powerful: you may use it for various source code tasks, from just finding all classes with print() method to executing an extremely complex refactoring transformation.

JTL is very easy to use, its intuitive query-by-example syntax makes it really easy to write JTL queries. For example,

public static double method(int, int);

matches all static methods that receive two int parameters and return a double. And the following query

classWithFactory := is T, class { 
    no public constructor; 
    public static T method;
}

matches all factory classes - classes having no public constructor, but instance factory method.

Additional JTL examples may be found in JTL Language Tour. The examples above come from this excellent manual too.

The JTL was initially described in the JTL - The Java Tools Language paper and developed at the Computer Science department at the Technion. But now, after a years of development, JTL goes open source at sourceforge. There is no blog or RSS feed there yet, but I hope those will appear soon.

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Online unique identity is not here yet

Boris Kirzner — Sat, 26 Jul 2008 12:10:44 +0000

Though claiming a blog at Technorati Profile is not so painful a it looks.

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Hibernate annotations: The many-to-many association with composite key

Boris Kirzner — Sat, 19 Jul 2008 19:12:14 +0000

Also many-to-many associations are usually referenced as a bad design solution, they are widely used in almost all modern database-centric applications (especially in those built around the existing legacy database). The very common scenario is a case when you not only need to handle a many-to-many association but also hold some additional property on the association.

In a J2EE world, Hibernate still remains the most popular ORM tool (or the JPA provider, if you wish). But implementing such a scenario with Hibernate Annotations is not so simple as you might imagine.

First of all, in the good old spirit of the Hibernate community, there is almost no documentation about many-to-many associations and composite keys (two paragraphs stating that there is @ManyToMany and @EmbeddedId annotations are not considered a documentation).

And the second hope of every open-source tool consumer, the world wide web community, provides almost no help: everybody are referencing the same post by Marcel Panse, written in April 2006. Though Marsel’s post is very clean and descriptive, it become outdated and the solution provided there is simply not working with the latest versions of Hibernate Annotations.

So I had to reinvent the wheel by my own, based on Marsel’s sample. Below is the solution working with Hibernate Annotations 3.3.1.GA.

The database part is the same: we have three tables (item, product and product_item), two POJO classes, and two classes for a many-to-many association and its primary key. The main difference from Marsel’s solution is that I’m not using any kind of “fake” properties on ProductItem in order to reference Item and Product, but just a plain transient properties delegating to ProductItemPk.

@Entity
@Table(name = "item")
public class Item {
 
    private Integer id;
    private String name;
    private List productItems = new LinkedList();
 
    public Item() {
    }
 
    @Id
    @GenericGenerator(name = "generator", strategy = "increment")
    @GeneratedValue(generator = "generator")
    @Column(name = "item_id", nullable = false)
    public Integer getId() {
        return this.id;
    }
 
    public void setId(Integer id) {
        this.id = id;
    }
 
    @Column(name = "name")
    public String getName() {
        return this.name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.item")
    public List getProductItems() {
        return this.productItems;
    }
 
    public void setProductItems(List productItems) {
        this.productItems = productItems;
    }
}

@Entity
@Table(name = "product")
public class Product {
 
    private Integer id;
    private String name;
    private List productItems = new LinkedList();
 
    public Product() {
    }
 
    @Id
    @GenericGenerator(name = "generator", strategy = "increment")
    @GeneratedValue(generator = "generator")
    @Column(name = "product_id", nullable = false)
    public Integer getId() {
        return this.id;
    }
 
    public void setId(Integer id) {
        this.id = id;
    }
 
    @Column(name = "name")
    public String getName() {
        return this.name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.product")
    public List getProductItems() {
        return this.productItems;
    }
 
    public void setProductItems(List productItems) {
        this.productItems = productItems;
    }
}

Note the two important points: ProductItem has two transient properties for Product and Item (since an unidirectional relationships will be meaningless here) and a use of @AssociationOverrides annotation to specify the database columns

@Entity
@Table(name = "product_item")
@AssociationOverrides({
@AssociationOverride(name = "pk.item", joinColumns = @JoinColumn(name = "item_id")),
@AssociationOverride(name = "pk.product", joinColumns = @JoinColumn(name = "product_id"))
        })
public class ProductItem {
 
    private ProductItemPk pk = new ProductItemPk();
 
    @EmbeddedId
    private ProductItemPk getPk() {
        return pk;
    }
 
    private void setPk(ProductItemPk pk) {
        this.pk = pk;
    }
 
    @Transient
    public Item getItem() {
        return getPk().getItem();
    }
 
    public void setItem(Item item) {
        getPk().setItem(item);
    }
 
    @Transient
    public Product getProduct() {
        return getPk().getProduct();
    }
 
    public void setProduct(Product product) {
        getPk().setProduct(product);
    }
 
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
 
        ProductItem that = (ProductItem) o;
 
        if (getPk() != null ? !getPk().equals(that.getPk()) : that.getPk() != null) return false;
 
        return true;
    }
 
    public int hashCode() {
        return (getPk() != null ? getPk().hashCode() : 0);
    }
}

@Embeddable
public class ProductItemPk implements Serializable {
 
    private Item item;
    private Product product;
 
    @ManyToOne
    public Item getItem() {
        return item;
    }
 
    public void setItem(Item item) {
        this.item = item;
    }
 
    @ManyToOne
    public Product getProduct() {
        return product;
    }
 
    public void setProduct(Product product) {
        this.product = product;
    }
 
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
 
        ProductItemPk that = (ProductItemPk) o;
 
        if (item != null ? !item.equals(that.item) : that.item != null) return false;
        if (product != null ? !product.equals(that.product) : that.product != null)
            return false;
 
        return true;
    }
 
    public int hashCode() {
        int result;
        result = (item != null ? item.hashCode() : 0);
        result = 31 * result + (product != null ? product.hashCode() : 0);
        return result;
    }
}

Hope this helps.

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Good coders, maybe. Awful product managers, definetely.

Boris Kirzner — Thu, 03 Apr 2008 20:03:15 +0000

The discussion is probably one of the best examples to the simple rule: programmers should never ever be allowed to lead a product design.

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The rule of thumb

Boris Kirzner — Thu, 03 Jan 2008 09:12:30 +0000

If you may configure something using Spring — never ever try to configure the same thing with Hibernate.

Sorry, Gavin.

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Is the modern software getting more and more humanlike?

Boris Kirzner — Thu, 20 Dec 2007 17:10:47 +0000

The colleague of mine just got this from his IntelliJ IDEA 7.0.2:

At least it apologizes…

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Good old IE bug?

Boris Kirzner — Mon, 12 Nov 2007 12:54:01 +0000

May someone explain me why the following HTML code is causing IE6 SP2 crash?

 xmlns="http://www.w3.org/1999/xhtml">


    
        
             style="table-layout:fixed">
                 width="20"/>

Bonus: CodeColorizer

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Playing around with IntelliJ IDEA 7

Boris Kirzner — Tue, 30 Oct 2007 08:11:06 +0000

There is something charming in those small things IDE developers make for us.

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Mainsoft makes one more step forward to developing Grasshopper community

Boris Kirzner — Wed, 11 Jul 2007 12:52:08 +0000

This week Mainsoft introduced a new source of information for all Grasshopper users: «The Grasshoppers» blog.

Although currently there is only one person actually blogging there, this is a promising step forward to developing a rich community of both Grasshopper users and developers.

By the way, it worth to take a look at full Grasshopper bloggers list.

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