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Implementing a custom unique random identity generator

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kerchunk

Post subject: Implementing a custom unique random identity generator

Posted: Thu Aug 19, 2010 6:38 pm

Beginner

Joined: Tue Aug 03, 2010 4:32 pm
Posts: 22

Greetings,

All my data tables in my database have a BIGINT field named "id" as their pk.
NONE of them use the AUTO_INCREMENT feature - instead I have a table named
Used_Random_Longs consisting of fields:
--- random_long BIGINT(12) unsigned PRIMARY KEY,
--- used_in_table varchar(30)

Inserting a row into a data table consists of:
a--using a stored procedure to generate random BIGINTs until one
successfully INSERTs into UsedRandomLongs then returning
successfulbigint
b--insert the desired data into a new row of the data table then perform an
UPDATE UsedRandomLongs
SET used_in_table = datatablename
WHERE id = successfulbigint

Thus I can guarantee every id is unique across the database and know at a glance which table it's used in.

Now I'd like to build a custom identity generator to achieve the same thing.

So far I've got this

Code:

package dogs.model;

import org.hibernate.*;
import org.hibernate.engine.SessionImplementor;
import org.hibernate.id.Configurable;
import org.hibernate.id.IdentifierGenerator;
import org.hibernate.HibernateException;
import org.hibernate.MappingException;
import org.hibernate.dialect.Dialect;

import org.hibernate.type.Type;

import java.io.Serializable;
import java.sql.*;

import utils.*;

import static org.hibernate.criterion.Expression.*;

import java.util.*;

public class UniqueLongIdGenerator implements IdentifierGenerator
{

     public Serializable generate(SessionImplementor session, Object object) throws HibernateException
     {
       Long out_llng = -1L;
        UsedRandomLongs uri = null;

        Random rand_generator = new Random();
        
        do {
              out_llng = rand_generator.nextLong() & 0xE8D4A50FFF; // masks to 0 - 999999999999
              uri = new UsedRandomLongs();
        } while ( !session.save( uri, out_llng;
        return out_llng;
     }

}

and

Code:

package dogs.model;

import org.hibernate.*;
import org.hibernate.cfg.*;
import org.hibernate.Query;
import org.hibernate.context.ManagedSessionContext;
import javax.persistence.*;

import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.event.ActionEvent;

import utils.*;

import java.util.Arrays;

@Entity
@Table(name="Used_Random_Longs")
public class UsedRandomLongs
{
    @Id
    @Column(name="random_long")
    private Long id;
    private String used_in_table;

    //constructor
    UsedRandomLongs() {
        this.used_in_table = "pending";
    }

    ........

and one class that's been mapped to a data table

Code:

package dogs.model;

import org.hibernate.*;
import org.hibernate.cfg.*;
import org.hibernate.Query;
import org.hibernate.context.ManagedSessionContext;
import javax.persistence.*;

import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.event.ActionEvent;

import utils.*;

import java.util.Arrays;

@Entity
@Table(name="Frogs")
public class Frogs
{
    @Id
    @GeneratedValue(generator="UniqueLongIdGenerator")
    @Column(name="random_integer")
    private Long id;

    ........

Any help/hints/suggestions/constructive criticisms and examples are all appreciated!

Still-learning Steve

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kerchunk

Post subject: Re: Implementing a custom unique random identity generator

Posted: Mon Aug 23, 2010 6:44 pm

Beginner

Joined: Tue Aug 03, 2010 4:32 pm
Posts: 22

Hm, no takers. Allright let's make the problem simpler. My custom id generator now just spits out a random long

Code:

public class UniqueLongIdGenerator implements IdentifierGenerator, Configurable
{
   private String tableName;
   
   public void configure( Type arg0, Properties props, Dialect arg2 ) throws MappingException {  
       setTableName( props.getProperty( "tableName" ) );  
   } 

     public Serializable generate( SessionImplementor session, Object object) throws HibernateException
     {
         Long out_llng = -1L;
       
          Random rand_generator = new Random();
             
          return rand_generator.nextLong();

     }
     
     // getter & setter for the configurable parameters  
     public String getTableName() {  
         return tableName;  
     }  
     public void setTableName( String aa ) {  
         this.tableName = aa;  
     }  

}

and my entity class

Code:

@Entity
@Table(name="Logs")
public class Log
{
    @Id
    @GeneratedValue(generator="UniqueLongIdGenerator")
    @GenericGenerator(name="UniqueLongIdGenerator",
                    strategy="UniqueLongIdGenerator",
                    parameters = { @Parameter(name="tableName", value="Log")}
    )
    @Column(nullable=false)
    private Long id
    ....

I do have a <mapping class="foo.UniqueLongIdGenerator"/> statement in my hibernate.cfg.xml file.

When I try to execute the above I get the "unknown id.generator" error. What must I do/undo/modify to solve this? The manuals seem to be somewhat vague on the detaills of implementation.

TIA,

Still-learning Steve

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kerchunk

Post subject: Re: Implementing a custom unique random identity generator

Posted: Tue Aug 24, 2010 12:05 am

Beginner

Joined: Tue Aug 03, 2010 4:32 pm
Posts: 22

Turns out the strategy parameter needs to be a fully qualified path to the class of the generator:

Code:

    @Id
    @GeneratedValue(generator="MyCustomGenerator")
    @GenericGenerator(name="MyCustomGenerator",
                    strategy="forests.model.UniqueLongIdGenerator",
                    parameters = { @Parameter(name="tableName", value="Log")}

So the simplified case works now, yea.

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kerchunk

Post subject: Re: Implementing a custom unique random identity generator

Posted: Tue Aug 24, 2010 9:56 pm

Beginner

Joined: Tue Aug 03, 2010 4:32 pm
Posts: 22

I was able to solve the more complex problem by moving the generate-unique-random-bigint code into the database itself via a called stored procedure. This reduced the custom identity generator to:

Code:

public class UniqueLongIdGenerator implements IdentifierGenerator, Configurable
{
   private String tableName;
   
   public void configure( Type arg0, Properties props, Dialect arg2 ) throws MappingException {  
       setTableName( props.getProperty( "tableName" ) );  
   } 

     public Serializable generate( SessionImplementor session, Object object) throws HibernateException
     {
       Long out_llng = -1L;
       
       try {
            String sqlcmd = "{call get_random_bigint( ?, ?)}";
            Connection conn = session.connection();
            CallableStatement cs = conn.prepareCall( sqlcmd);
            //set input parameter
            cs.setString( 1, tableName);
            //set output parameter
            cs.registerOutParameter( 2, java.sql.Types.BIGINT);
            cs.execute();
            //exctract returned value
            out_llng = cs.getLong(2);
       } catch ( SQLException e) {
          System.out.println( "UhOh, " + e);   
       }

        return out_llng;
     }
     
     // getter & setter for the configurable parameters  
     public String getTableName() {  
         return tableName;  
     }  
     public void setTableName( String aa ) {  
         this.tableName = aa;  
     }  

}

So now in main() :

Code:

Log aLog = new Log();
sess.save(aLog);

has the effect of creating a new Log object with a random Long as an id and the id being guaranteed to be unique within the database by entering the row
random_bigint:'Logs'
into the UsedRandomInteger table

CASE CLOSED

Still-learning Steve

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