So how about some JPA? First get a JEE eclipse build, and install JPA tools and eclipse link. Next download a postgres JDBC driver, eclipse JPA implementation and OpenJPA – JPA support for J2SE.

You should now be able to use the New… Other… JPA… “Entities from tables” option. Create a database connection and enter username/password etc. and the JDBC driver jar etc.

Here we’ve created an entity for Horse and Rider.

@Entity
@Table(name = "horses")
public class Horse {

    @Id
    @Column(name = "id")
    private int id;

    @Column(name = "name")
    private String name;

    @Column(name = "size")
    private int size;

    @OneToMany(fetch = FetchType.EAGER)
    @JoinTable(name = "horses_riders", joinColumns = @JoinColumn(name = "hid"), inverseJoinColumns = @JoinColumn(name = "rid"))
    private Collection<Rider> riders;

    public Horse() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getSize() {
        return size;
    }

    public void setSize(int size) {
        this.size = size;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public Collection<Rider> getRiders() {
        return riders;
    }
}

@Entity
@Table(name = "riders")
public class Rider {
    @Id
    @Column(name = "id")
    private int id;

    @Column(name = "name")
    private String name;

    @OneToMany(fetch = FetchType.EAGER)
    @JoinTable(name = "horses_riders", joinColumns = @JoinColumn(name = "rid"), inverseJoinColumns = @JoinColumn(name = "hid"))
    private Collection horses;

    public Rider() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Collection<Horse> getHorses() {
        return horses;
    }
}

A fairly basic setup would be as follows:

    EntityManagerFactory factory = Persistence.createEntityManagerFactory(
            "horses", System.getProperties());

    EntityManager em = factory.createEntityManager();

    Query horseQuery = em.createQuery("SELECT h FROM Horse h");

    for (Horse horse : (List<Horse>) horseQuery.getResultList()) {
        System.out.println(horse.getName() + horse.getRiders());
    }

The META-INF/persistence.xml file defines the entities and postgres connection info.

<?xml version="1.0" encoding="UTF-8"?>

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.0">
<persistence-unit name="horses">
<provider>org.apache.openjpa.persistence.PersistenceProviderImpl
</provider>

<class>hellojpa.Horse</class>
<class>hellojpa.Rider</class>

<properties>

<property name="openjpa.ConnectionDriverName" value="org.postgresql.Driver" />
<property name="openjpa.ConnectionURL" value="jdbc:postgresql://localhost:5432/horsedb" />

<property name="openjpa.ConnectionUserName" value="horse" />
<property name="openjpa.ConnectionPassword" value="password" />

<property name="openjpa.DynamicEnhancementAgent" value="true" />
<property name="openjpa.RuntimeUnenhancedClasses" value="supported" />
</properties>
</persistence-unit>

</persistence>

So we’ve got a table of horses. Let’s make another table, and get get busy with an association table and some JOINs. First we have to add a primary key to our horse table so we can reference it elsewhere.

The easy way:

ALTER TABLE horses ADD COLUMN id SERIAL;

The hard way: This explains how auto-increment really works in postgres – it actually uses a sequence owned by the table column that uses it.

# Steps to make a sequence.
ALTER TABLE horses ADD COLUMN id INT UNIQUE;
ALTER TABLE horses ALTER COLUMN id NOT NULL;
ALTER TABLE horses ADD PRIMARY KEY (id);
CREATE SEQUENCE horses_id_seq;
ALTER TABLE horses ALTER COLUMN id SET DEFAULT NEXTVAL('horses_id_seq');
ALTER SEQUENCE horses_id_seq OWNED BY horses.id;

Now let’s create table of riders.

CREATE TABLE riders (name VARCHAR(255), id SERIAL PRIMARY KEY);
INSERT INTO riders (name) VALUES ('adam');
INSERT INTO riders (name) VALUES ('bob');
INSERT INTO riders (name) VALUES ('charlie');

Now we create an association table linked horses with riders.

CREATE TABLE horses_riders (hid INT REFERENCES horses(id),
                            rid INT REFERENCES riders(id));

INSERT INTO horses_riders (hid, rid) VALUES (1,1);
INSERT INTO horses_riders (hid, rid) VALUES (2,3);

Using the association table. First the naive, inefficient way. This is bad because it makes all possible comparisons.

SELECT r.name,h.name FROM horses h, riders r,horses_riders ass
                     WHERE ass.hid = h.id AND ass.rid = r.id;
  name   |     name
---------+--------------
 adam    | Mr Ed
 charlie | glue factory

Now joins, there are various varieties, but the simplest to understand is simple “table1 JOIN table2 ON condition”.

SELECT * from (horses h JOIN horses_riders ass ON ass.hid = h.id);
     name     | size | id | hid | rid
--------------+------+----+-----+-----
 Mr Ed        |  456 |  1 |   1 |   1
 glue factory |  123 |  2 |   2 |   3

SELECT * from (riders r JOIN horses_riders ass ON ass.rid = r.id);
  name   | id | hid | rid
---------+----+-----+-----
 adam    |  1 |   1 |   1
 charlie |  3 |   2 |   3

We can combine two joins to see who owns which horses.

SELECT r.name, h.name from
      (horses_riders ass JOIN horses h ON ass.hid = h.id)
      JOIN riders r ON ass.rid = r.id;

  name   |     name
---------+--------------
 adam    | Mr Ed
 charlie | glue factory

1. Download and build it.

wget http://ftp.postgresql.org/pub/source/v9.1.3/postgresql-9.1.3.tar.bz2
tar xjf postgresql-9.1.3.tar.bz2
cd postgresql-9.1.3
sudo apt-get install libreadline-dev zlib1g-dev
./configure --prefix=$(pwd)/local
make install

2. Initialize and run. Setup a database, with a root user, prompt for password.

export LD_LIBRARY_PATH=local/lib:$LD_LIBRARY_PATH
export PATH=local/bin:$PATH
initdb -U root -W datadir
postgres -D datadir

3. Create a regular user and a database.

createuser -U root horse -W
Shall the new role be a superuser? (y/n) n
Shall the new role be allowed to create databases? (y/n) n
Shall the new role be allowed to create more new roles? (y/n) n
createdb horsedb -U root -O horse

4. Connect as regular user, create a table and insert some data, then select it.

psql horsedb -U horse
CREATE TABLE horses (name VARCHAR(255), size INT);
INSERT INTO horses (name, size) VALUES('glue factory', 123);
INSERT INTO horses (name, size) VALUES('Mr Ed', 456);
SELECT * FROM horses;
     name     | size
--------------+------
 glue factory |  123
 Mr Ed        |  456
\q

On the Mac (Intel iMac 10.7), system preferences, energy saver, wake for ethernet network access.

On Linux (Ubuntu 11.04)

# Grab the MAC address out of the ARP table (assuming still on)
ping horse.lan
/usr/sbin/arp -a
horse.lan (10.5.1.62) at 00:12:23:34:45:56 [ether] on eth0

# install etherwake
sudo install etherwake
etherwake -i eth0  00:12:23:34:45:56

# now awake
ssh horse.lan

# do stuff
horse:$ scp /Users/AnnaChapman/Desktop/secret_docs.tar.gz julian@wikileaks.org:/home/julian/nextrelease

# power off again
horse:$ pmset sleepnow

This works, the mac powers on. However the screen stays off, but you can still ssh in, do whatever and put it back to sleep.

I came to resurrect a year old project last week, which previously worked fine, under Ubuntu 11.10. BOOM! nothing works. The project is a CLI TCP server to control a USB opendmx widget using FTD2XX with an Android app client.

First a random g++ fail.

g++ -I. -lpthread -lstdc++ -lftd2xx  *.cpp -o opendmxserver
DmxTransmit.cpp:(.text+0x38): undefined reference to `FT_ListDevices'
DmxTransmit.cpp:(.text+0xdb): undefined reference to `FT_Open'
/tmp/cccTckgn.o: In function `Mutex::Mutex()':
Mutex.cpp:(.text+0x1e): undefined reference to `pthread_mutexattr_init'
/tmp/ccs5TdOM.o: In function `System::currentTimeMillis()':
System.cpp:(.text+0x15): undefined reference to `clock_gettime'
/tmp/ccCEDMng.o: In function `Thread::start()':
Thread.cpp:(.text+0x6c): undefined reference to `pthread_create'

So what’s that all about, well it turns out now you have to put the linker switches after the *.cpp. So this works.

g++ -I. *.cpp -o opendmxserver -lpthread -lstdc++ -lftd2xx

Next fail. Runtime weirdness, assert fail.

opendmxserver: tpp.c:63: __pthread_tpp_change_priority: Assertion `new_prio == -1 || (new_prio >= __sched_fifo_min_prio && new_prio <= __sched_fifo_max_prio)' failed.

YFKM, it turns out that out that you need to call pthread_mutexattr_init on the pthread_muxexattr_t structure. This did not used to be the case, although it makes sense to initialize all your structs…

pthread_mutexattr_t attr;
pthread_mutexattr_init(&attr); // not previously required
pthread_mutex_init (&this->mutex, &attr);

Following error message seen when manipulating bookmarks with VBA in Word.

Word has insufficient memory. You will not be able to undo this action once it is
completed. Do you want to continue?”

Fix: Clear the undo buffer as you go along.

ActiveDocument.UndoClear