The [Dynamic, typesafe queries in JPA 2.0][1] article is a very good one on this topic, actually the best one I&#39;ve found so far **online**, even better than the [Chapter 23 Using the Criteria API to Create Queries][2] from the Java EE 6 tutorials (that contains some mistakes).

  [1]: http://www.ibm.com/developerworks/java/library/j-typesafejpa/
  [2]: http://download.oracle.com/javaee/6/tutorial/doc/gjitv.html

Examples of common queries are [here][1]

All examples are in this form:

    CriteriaBuilder cb = em.getCriteriaBuilder();
     
    // Query for a List of objects.
    CriteriaQuery cq = cb.createQuery();
    Root e = cq.from(Employee.class);
    cq.where(cb.greaterThan(e.get(&quot;salary&quot;), 100000));
    Query query = em.createQuery(cq);
    List&lt;Employee&gt; result = query.getResultList();


----------

If you are also considering other technologies you should seriously consider [querydsl][2]. Main advantages over criteria include shorter code, good readability and similar syntax to regular sql.

Example QueryDSL code here:

    JPAQuery query = new JPAQuery(entityManager);
    List&lt;Person&gt; persons = query.from(person)
      .where(
        person.firstName.eq(&quot;John&quot;)),        
      .list(person);


  [1]: http://en.wikibooks.org/wiki/Java_Persistence/Criteria
  [2]: http://www.querydsl.com/

Pro JPA 2: Mastering the Java Persistence API
http://books.google.com/books?id=j84hdeHH2PYC

This is the source I find the most useful.

http://www.altuure.com/2010/09/23/jpa-criteria-api-by-samples-part-i/

My project has a `UIImage` category function that I want to call from another class. I properly import the header file for the image category and I get the project to compile with no warning.

The problem is that when I call the `UIImage` category function I seen an unrecognized selector error with a `NSInvalidArgumentException`. Why am I seeing this if I&#39;ve properly linked everything?

    #import &lt;UIKit/UIKit.h&gt;
    
    @interface UIImage (DRShare)
    
    + (UIImage*) imageNamed:(NSString*)name;
    
    @end
   

    @implementation UIImage (DRShare)
    
    + (UIImage*) imageNamedDR:(NSString*)name{
    	
    	CGFloat s = 1.0f;
    	if([[UIScreen mainScreen] respondsToSelector:@selector(scale)]){
    		s = [[UIScreen mainScreen] scale];
    	}
    	
    	NSString *path = [NSString stringWithFormat:@&quot;%@%@%@.png&quot;,kImagesPath,name,s &gt; 1 ? @&quot;@2x&quot;:@&quot;&quot;];
    	return [UIImage imageWithContentsOfFile:DRBUNDLE(path)];
    }
    
    @end

file that calls it:
   
    		backgroundView = [[UIImageView alloc] initWithImage:[UIImage imageNamedDR:@&quot;Share Popup Background&quot;]];

exception raised:

    2010-10-22 11:51:02.880 Stuff[11432:207] +[UIImage imageNamedDR:]: unrecognized selector sent to class 0x1f8e938
    2010-10-22 11:51:02.883 Stuff[11432:207] *** Terminating app due to uncaught exception &#39;NSInvalidArgumentException&#39;, reason: &#39;+[UIImage imageNamedDR:]: unrecognized selector sent to class 0x1f8e938&#39;
    *** Call stack at first throw:
    (
    	0   CoreFoundation                      0x02e65b99 __exceptionPreprocess + 185
    	1   libobjc.A.dylib                     0x02fb540e objc_exception_throw + 47
    	2   CoreFoundation                      0x02e6776b +[NSObject(NSObject) doesNotRecognizeSelector:] + 187
    	3   CoreFoundation                      0x02dd72b6 ___forwarding___ + 966
    	4   CoreFoundation                      0x02dd6e72 _CF_forwarding_prep_0 + 50
    	5   TapTapShare                         0x0001291c -[DRShareViewController backgroundView] + 127
    	6   TapTapShare                         0x00012343 -[DRShareViewController loadView] + 639
    	7   UIKit                               0x0044f54f -[UIViewController view] + 56
    	8   UIKit                               0x0044d9f4 -[UIViewController contentScrollView] + 42
    	9   UIKit                               0x0045d7e2 -[UINavigationController _computeAndApplyScrollContentInsetDeltaForViewController:] + 48
    	10  UIKit                               0x0045bea3 -[UINavigationController _layoutViewController:] + 43
    	11  UIKit                               0x0045d12d -[UINavigationController _startTransition:fromViewController:toViewController:] + 524
    	12  UIKit                               0x00457ccd -[UINavigationController _startDeferredTransitionIfNeeded] + 266
    	13  UIKit                               0x00574b55 -[UILayoutContainerView layoutSubviews] + 226
    	14  QuartzCore                          0x02616481 -[CALayer layoutSublayers] + 177
    	15  QuartzCore                          0x026161b1 CALayerLayoutIfNeeded + 220
    	16  QuartzCore                          0x026160bd -[CALayer layoutIfNeeded] + 111

Objective-C Category Causing unrecognized selector

I&#39;m trying to generate a random date of birth for people in my database using a Java program. How would I do this?

Generate random date of birth

I&#39;ve been trying to find a JPA Criteria API tutorial but haven&#39;t been much successful. Do you know about any for beginners? I&#39;d like to start using it in an Java5/Maven app to build complex search queries. 

JPA Criteria Tutorial

<p>I've been trying to find a JPA Criteria API tutorial but haven't been much successful. Do you know about any for beginners? I'd like to start using it in an Java5/Maven app to build complex search queries.</p>


I need to get the length of a 2D array for both the row and column.  I’ve successfully done this, using the following code:

    public class MyClass {
    
     public static void main(String args[])
        {
      int[][] test; 
      test = new int[5][10];
      
      int row = test.length;
      int col = test[0].length;
      
      System.out.println(row);
      System.out.println(col);
        }
    }

This prints out 5, 10 as expected.

Now take a look at this line:

      int col = test[0].length;

Notice that I actually have to reference a particular row, in order to get the column length.  To me, this seems incredibly ugly.  Additionally, if the array was defined as:

    test = new int[0][10];

Then the code would fail when trying to get the length.  Is there a different (more intelligent) way to do this?










Getting the array length of a 2D array in Java

I&#39;m reading [Programming Scala][1]. At the beginning of chapter 4, the author comments that Java supports static methods, which are &quot;not-so-pure OO concepts.&quot; Why is this so?


  [1]: http://www.amazon.com/Programming-Scala-Multi-Core-Complexity-Programmers/dp/193435631X/ref=sr_1_3?ie=UTF8&amp;qid=1287801906&amp;sr=8-3

Why aren&#39;t static methods considered good OO practice?

I would like to implement a java application (server application) that can download a new version (.jar file) from a given url, and then update itself at runtime.

What is the best way to do this and is it possible?

I guess that the application can download a new .jar file and start it. But how should I do the handover, e.g. know when the new application is started and then exit. Or is there a better way to do this?

How can I write a Java application that can update itself at runtime?

What exactly is the technical difference between `console.writeline` and `System.out.println`? 
I know that `System.out.println` writes to standard output but is this not the same thing as the console? 

I do not fully understand the [documentation][1] for `console.writeline`. 

  [1]: http://download.oracle.com/javase/6/docs/api/java/io/Console.html


console.writeline and System.out.println

I have following code :

            

        System.out.println(&quot; | 1  2  3  4  5  6  7  8  9&quot;);
		System.out.println(&quot;----------------------------&quot;);
	    System.out.println(&quot;&quot;);

I use println to create a new line. Is it possible to do the same using \n or \r?
I tried to add \n to the second println statment and continue printing with the print method but \n does not create a new line.

any ideas?

Print in new line, java

I&#39;m trying to use Criteria API in my new project:

    public List&lt;Employee&gt; findEmps(String name) {
		CriteriaBuilder cb = em.getCriteriaBuilder();
		CriteriaQuery&lt;Employee&gt; c = cb.createQuery(Employee.class);
		Root&lt;Employee&gt; emp = c.from(Employee.class);
		c.select(emp);
		c.distinct(emp);
		List&lt;Predicate&gt; criteria = new ArrayList&lt;Predicate&gt;();
		
		if (name != null) {
			ParameterExpression&lt;String&gt; p = cb.parameter(String.class, &quot;name&quot;);
			criteria.add(cb.equal(emp.get(&quot;name&quot;), p));
		}

		/* ... */
		
		if (criteria.size() == 0) {
			throw new RuntimeException(&quot;no criteria&quot;);
		} else if (criteria.size() == 1) {
			c.where(criteria.get(0));
		} else {
			c.where(cb.and(criteria.toArray(new Predicate[0])));
		}
		
		TypedQuery&lt;Employee&gt; q = em.createQuery(c);
		
		if (name != null) {
			q.setParameter(&quot;name&quot;, name);
		}
		
		/* ... */
		
		return q.getResultList();
	}

Now when I change this line:

    			criteria.add(cb.equal(emp.get(&quot;name&quot;), p));
to:

    			criteria.add(cb.like(emp.get(&quot;name&quot;), p));

I get an error saying: 

&gt; The method like(Expression&lt;String&gt;, Expression&lt;String&gt;) in the type CriteriaBuilder is not &gt; applicable for the arguments (Path&lt;Object&gt;, ParameterExpression&lt;String&gt;)

What&#39;s the problem?


JPA/Criteria API - Like &amp; equal problem

Straight to the point, problem is saving the object Operator into MySQL DB.
Prior to save, I try to select from this table and it works, so is connection to db.

Here is my Operator object:

    @Entity
    public class Operator{
    
       @Id
       @GeneratedValue
       private Long id;
     
       private String username;
     
       private String password;
     
    
       private Integer active;
     
       //Getters and setters...
    }

To save I use JPA `EntityManager`’s `persist` method.

Here is some log:

    Hibernate: insert into Operator (active, password, username, id) values (?, ?, ?, ?)
    com.mysql.jdbc.JDBC4PreparedStatement@15724a0: insert into Operator (active,password, username, id) values (0, &#39;pass&#39;, &#39;user&#39;, ** NOT SPECIFIED **)

The way I see it, problem is configuration with auto increment but I can&#39;t figure out where.

Tried some tricks I&#39;ve seen here:
https://stackoverflow.com/questions/582526/hibernate-not-respecting-mysql-auto-increment-primary-key-field But nothing of that worked

If any other configuration files needed I will provide them.

DDL:

    CREATE TABLE `operator` ( 
    `id` INT(10) NOT NULL AUTO_INCREMENT,
    `first_name` VARCHAR(40) NOT NULL,
    `last_name` VARCHAR(40) NOT NULL,
    `username` VARCHAR(50) NOT NULL,
    `password` VARCHAR(50) NOT NULL,
    `active` INT(1) NOT NULL,
    PRIMARY KEY (`id`)
    )




How to annotate MYSQL autoincrement field with JPA annotations

I have a JPA entity with a property set as 

    @ManyToOne
    @Column(name=&quot;LicenseeFK&quot;)
    private Licensee licensee;

But when I deploy on JBoss 6 the application throws an error saying: 

    org.hibernate.AnnotationException: @Column(s) not allowed on a @ManyToOne property

I use Hibernate 3.5 as the JPA 2.0 implementation.

What should I use to reference the foreign key column?

@Column(s) not allowed on a @ManyToOne property

I have 

    private EntityManager em;

	public List getAll(DetachedCriteria detachedCriteria)	{

		return detachedCriteria.getExecutableCriteria(&quot;....&quot;).list();
	}
	
How can I retrieve the session if am using entitymanager, or how can I get the result from my detached criteria?


How can I get the session object if I have the entity-manager?

I was gathering information about the flush() method, but I&#39;m not quite clear when to use it and how to use it correctly. From what I read, my understanding is that the contents of the persistence context will be synchronized with the database, i. e. issuing outstanding statements or refreshing entity data.

Now I got following scenario with two entities `A` and `B` (in a one-to-one relationship, but not enforced or modelled by JPA). `A` has a composite PK, which is manually set, and also has an auto-generated IDENTITY field `recordId`. This `recordId` should be written to entity `B` as a foreign-key to `A`. I&#39;m saving `A` and `B` in a single transaction. The problem is that the auto-generated value `A.recordId` is not available within the transaction, unless I make an explicit call of `em.flush()` after calling `em.persist()` on `A`. (If I have an auto-generated IDENTITY PK then the value is directly updated in the entity, but that&#39;s not the case here.)

**Can `em.flush()` cause any harm when using it within a transaction?**

Correct use of flush() in JPA/Hibernate

Which annotation, **@Resource** ([jsr250][1]) or **@Autowired** (Spring-specific) should I use in DI?

I have successfully used both in the past, `@Resource(name=&quot;blah&quot;)` and `@Autowired @Qualifier(&quot;blah&quot;) `

My instinct is to stick with the `@Resource` tag since it&#39;s been ratified by the jsr people.  
Anyone has strong thoughts on this?

  [1]: http://jcp.org/en/jsr/detail?id=250



@Resource vs @Autowired

this is my code:

    @Column(columnName=&quot;firstname&quot;)
 

    private String firstName;
     
     @Column(columnName=&quot;lastname&quot;)
     private String lastName;
    
     public String getFirstName() {
      return firstName;
     }
    
     public void setFirstName(String firstName) {
      this.firstName = firstName;
     }
    
     public String getLastName() {
      return lastName;
     }
    
     public void setLastName(String lastName) {
      this.lastName = lastName;
     }

is it possible to read the value of my annotation @Column(**columnName**=&quot;xyz123&quot;) in another class?



Is it possible to read the value of a annotation in java?

    public class NaiveAlien extends Alien
    {
    
        @Override
        public void harvest(){}
    
    }


I was trying to understand my friend&#39;s code, and I do not get the syntax, @Override in the code. What does that do and why do we need in coding?
Thanks.

What does @Override mean?

I have tried to write a query statement with a subquery and an `IN` expression for many times. But I have never succeeded.

I always get the exception, &quot; Syntax error near keyword &#39;IN&#39; &quot;, the query statement was build like this,

    SELECT t0.ID, t0.NAME
    FROM EMPLOYEE t0
    WHERE IN (SELECT ?
              FROM PROJECT t2, EMPLOYEE t1
              WHERE ((t2.NAME = ?) AND (t1.ID = t2.project)))

I know the word before &#39;IN&#39; lose.

Have you ever written such a query? Any suggestion?

JPA 2.0, Criteria API, Subqueries, In Expressions

I have been using Hibernate Restrictions in JPA 1.0 ( Hibernate driver ). There is defined `Restrictions.ilike(&quot;column&quot;,&quot;keyword&quot;, MatchMode.ANYWHERE)` which tests if the keyword matching the column anywhere and it is case-insensitive. 

Now, I am using JPA 2.0 with EclipseLink as driver so I have to use &quot;Restrictions&quot; build-in JPA 2.0. I found `CriteriaBuilder` and method `like`, I have also found out how to make it matching anywhere ( although it is aweful and manual ), but still I haven&#39;t figured out how to do it case-insensitive.

There is my current aweful solution:

    CriteriaBuilder builder = em.getCriteriaBuilder();
    CriteriaQuery&lt;User&gt; query = builder.createQuery(User.class);
    EntityType&lt;User&gt; type = em.getMetamodel().entity(User.class);
    Root&lt;User&gt; root = query.from(User.class);
   
    // Where   
    // important passage of code for question  
    query.where(builder.or(builder.like(root.get(type.getDeclaredSingularAttribute(&quot;username&quot;, String.class)), &quot;%&quot; + keyword + &quot;%&quot;),
            builder.like(root.get(type.getDeclaredSingularAttribute(&quot;firstname&quot;, String.class)), &quot;%&quot; + keyword + &quot;%&quot;),
            builder.like(root.get(type.getDeclaredSingularAttribute(&quot;lastname&quot;, String.class)), &quot;%&quot; + keyword + &quot;%&quot;)
            ));

    // Order By
    query.orderBy(builder.asc(root.get(&quot;lastname&quot;)),
                builder.asc(root.get(&quot;firstname&quot;)));

    // Execute
    return em.createQuery(query).
                setMaxResults(PAGE_SIZE + 1).
                setFirstResult((page - 1) * PAGE_SIZE).
                getResultList();

**Questions:**

Is there any function like in Hibernate driver? 

Am I using the JPA 2.0 criteria correctly? This is awkward and uncomfortable solution in compare to Hibernate Restrictions.

Or can anybody help me how to change my solution to be case-insensitive, please?

Thanks a lot.


JPA2: Case-insensitive like matching anywhere

Which of the following collection types do you use in your JPA domain model and why:

 - `java.util.Collection`
 - `java.util.List`
 - `java.util.Set`

I was wondering whether there are some ground rules for this.

**UPDATE** I know the difference between a `Set` and a `List`. A `List` allows duplicates and has an order and a `Set` cannot contain duplicate elements and does not define order. I&#39;m asking this question in the context of JPA. If you strictly follow the definition, then you should always end up using the `Set` type, since your collection is stored in relational database, where you can&#39;t have duplicates and where you have define an order by yourself, i.e. the order in you Java `List` is not necessarily preserved in the DB.

For example, most of the time I&#39;m using the `List` type, not because it has an order or allows duplicates (which I can&#39;t have anyway), because some of the components in my component library require a list.


Which Java Type do you use for JPA collections and why?

I am using JPA 2.0 and hibernate. I have a User class and a Group class as follows:

    public class User implements Serializable {
        @Id
        @Column(name=&quot;USER_ID&quot;)
        private String userId;
    
        @ManyToMany
        @JoinTable(name = &quot;USER_GROUP&quot;,
                   joinColumns = {
                       @JoinColumn(name = &quot;GROUP_ID&quot;)
                   },
                   inverseJoinColumns = {
                       @JoinColumn(name = &quot;USER_ID&quot;)
                   }
        )
        private Set&lt;Group&gt; groupList;
        
        //get set methods
    }

    public class Group
    {
        @Id
        @Column(name=&quot;GROUP_ID&quot;)
        private String groupId;
    
        @ManyToMany(mappedBy=&quot;groupList&quot;)
        private Set&lt;User&gt; memberList;
        //get set methods
    }

And then, I create a user and group and then assign the user to the group.

What I want to have is when I delete the group, the group will be deleted (of course) and all the user-group relationship that the group has will be automatically deleted from the USER_GROUP join table but the user itself is not deleted from the USER table.

With the code I have above, only the row in the GROUP table will be deleted when I delete a group and the user will still have an entry to the deleted group in the USER_GROUP join table.


If I put cascade in the User class like this:

    @ManyToMany(cascade=CascadeType.ALL)
    @JoinTable(name = &quot;USER_GROUP&quot;,
    joinColumns =
    {
        @JoinColumn(name = &quot;GROUP_ID&quot;)
    },
    inverseJoinColumns =
    {
        @JoinColumn(name = &quot;USER_ID&quot;)
    })
    private Set&lt;Group&gt; groupList;
When I delete the group, the user will be deleted as well!

Is there any way to achieve what I want?

Content Type	Original Author	Original Content on Stackoverflow
Question	John Manak	View Question on Stackoverflow
Solution 1 - Java	Pascal Thivent	View Answer on Stackoverflow
Solution 2 - Java	Marcin Szymczak	View Answer on Stackoverflow
Solution 3 - Java	John Manak	View Answer on Stackoverflow
Solution 4 - Java	Aaron Saunders	View Answer on Stackoverflow

JPA Criteria Tutorial

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Solution 4 - Java

Generate random date of birth

Objective-C Category Causing unrecognized selector

Attributions