PHP MySQL tips

Monday, August 6th, 2007

Interesting PHP MySQL tips.

Some comments:

2. Always prepend the table name to the field. E.g. ProductName, SupplierPostCode.

This refers to field name aliasing, not to actual field names. He doesn’t suggest that you actually name your fields like that in the table, but only when you select them: SELECT product.name AS product_name instead of SELECT product.product_name. The only real reason I can think of why you’d want to do this is for easier selecting the values in the calling code. I don’t see why it would make joins easier, as it’s just as easy to type JOIN order ON order.product_id = product.id, IMHO.

3. Always create a primary id field with the name of the table followed by the id. e.g. ProductID

Two things I don’t agree with. First, it’s not always necessary to create a primary id field. You should only add an ID field if there’s no unique key for that table. Second, I don’t think prepending the tablename to the ID field is a good idea for primary id fields. It’s not really bad either, but I like a plain ‘product.id’ field better, because you can instantly recognise the unique identifier field for that table. Foreign key fields, on the other hand, do feel better with their tablename prepended: order.product_id refers to product.id.

5. Use a separate logging table or transactions for logs of table updates, deletes etc.

We usually create a duplicate table for every table in the database, and name it ‘tableHistory’ or something like that. Then we add some metadata fields to the history table (time, user, mutationtype, etc) and place triggers on each table so that any mutation will insert the old row into the history table for that table, along with some metadata. That way, you always have a complete history of every mutation in your database. Great for auditing, plus you can create generic ‘Last changed by foo on bar’ functionality very easily.

How I get my music and movies

Sunday, August 5th, 2007

I don’t buy music CDs. They’re more expensive than they should be, and the prices never drop, even if the CDs are old. I don’t buy music online either, since it’s usually even more expensive than a CD, it has stupid DRM (Digital Restriction Management) restrictions, and you don’t even get the nice booklet. How can something that has no costs for physical production, worse quality than the real product and less value for your money cost more than the real thing? I don’t buy movies (DVDs) either, because there’s all kinds of restrictive stuff on them such as regions and DRM copy restrictions.

DRM that’s meant to keep you from copying media is illegal in the Netherlands. We’ve got a law that says you can make backup copies of media you buy. Fair-use probably also allows me to convert media I’ve bought so that I can listen to it in my car (if I had one), or on whatever device I happen to have. It’s also legal in the Netherlands to make copies of music and movies for your friends. Since DRM prevents these things, it’s illegal. Why would I buy a product that is too expensive, restricts my rights and is also illegal?

Instead of buying content, I download it. I download massive amounts of music and movies, and I never pay for any of it. And I don’t have to feel guilty about it, because it’s legal in the Netherlands. I can download as much as I want, but distributing contents is illegal (unless it’s to some close friends).

In the Netherlands, we pay a tax on empty CDs and DVDs. Legislators assume everybody buying empty, writeable media is a criminal. It’s not even a case of “Guilty until proven innocent”, because there’s no way to escape the tax, short of illegally importing empty media from across the border. What if I just want to make backups of my personal files? The money’s supposed to go to the record companies. It doesn’t always get there apparently, but it’s the idea that counts. I don’t want my money to go to the record companies, because they’re greedy bastards that keep breaking the law and violating my rights. So I don’t buy empty media either. I’ve got a big fat Internet connection and harddisk space is cheap, so why would I keep my stuff on CDs or DVDs?

I don’t have to feel sorry for the artists either. They get their money from the tax on empty media. Except from me of course. But if the law can be ambiguous, so can I. Besides, those poor artists should stand up to their record companies and distributors and demand fairly priced CDs and DVDs and renounce DRM.

I’ve got 8000 pieces of music on my computer. Let’s say the average CD contains eight songs. That’s a thousand CDs. I’d consider €10,- for a CD that’s just been released a fair price. An older CD, say, a year old, should cost a maximum of €5,- to €7,- euro’s. So let’s say €6,-. Most of my music was older than a year by the time I downloaded it. Perhaps 2% was just released. That would be twenty CDs.

20 x €10,- = €200,-
980 x €6,- = €5880,-
Total: €6080,-

So, the record industry could have had approximately €6000,- of my money in their pocket instead of €0,-, all because they’re greedy bastards. Too bad folks, but I don’t really feel sorry for you.

Here’s what the government should do:

• Remove the tax on empty media.
• Break the Record Industry’s cartel
• Demand fair prices on CDs
• Outlaw Digital Restriction Management when it breaks the law.

Did you know? Common myths

Saturday, August 4th, 2007

There are some myths out there which are just blatantly false, but that are really pervasive:

• Water in a sink on one hemisphere does not flow from the sink the other way than on the other hemisphere. There is such a thing as the Coriolis force, which (basically) describes the deflection in the path of an object moving on a rotating sphere due to its inertia. The Coriolis force does explain why cyclones rotate in the opposite direction on the northern hemisphere than on the southern hemisphere. But the force is simply way too small to have any effect on the rotation of water draining from a sink.
• Hair is not alive, it’s dead. The only thing alive is the hair-sack beneath the skin, from which the hair grows. Same goes for nails, as both consist of keratin
• Split hair-ends cannot be mended. Once split, they stay split. Apparently, some products out there will glue them back together temporary, but after it wears off, the ends split again.
• Hair does not grow back thicker when you shave it. It just appears that way because the hair-stems are thicker than the ends.
• Your hair cannot turn gray all at once if something scares you.
• Going swimming after having eaten something will not give you cramps and make you drown.

I thought about citing references, but that would be useless. People who believe (and keep perpetuating) these myths are apparently hellbent on keeping those beliefs, no matter how much evidence you show them that it’s false. For the others out there, google around a bit. You’ll find enough information dispelling these myths.

Gnome/Metacity keybindings and other customizations

Thursday, August 2nd, 2007

I never really liked Gnome because I couldn’t make Metacity act the way I like it.

I’m used to WindowMaker, and it has very configurable keybindings for managing windows. For instance, it’s quite easy to map a keybinding like <Control><Alt>-; to an action that maximizes the currently focussed window horizontally. Another keybinding maximizes the window vertically. These are very useful options for me, since I use terminal windows a lot.

Another annoying thing about Gnome/Metacity was that you could have a keybinding which maximized the currently focussed window, but pressing that keybinding again wouldn’t bring the window back to the original size. This is another feature is use all the time, because I often need to have more screen real estate for my terminal window for a short while (so that I can see more of the terminal output buffer).

Something else I missed from WindowMaker is binding keybindings to programs in the menu so that, say, <Win>-e opened my editor. This didn’t seem possible in Gnome/Metacity, and I didn’t want to use a third-party application for it, because that doesn’t integrate nicely with Gnome (and will therefore cause strange behaviour, such as conflicting keybindings in applications).

In the past, I’ve given Gnome a couple of tries, but everytime I switched back to WindowMaker after a little while because of the lack of proper keybindings. A couple of days ago I decided to give Gnome another try, because I’m planning on installing Ubuntu (currently running Debian GNU/Linux) somewhere in the near future. Quite by accident, I stumbled upon the fact that Gnome/Metacity does support all the keybindings I’m used to. All you have to do is dive into the GConf registry a bit.

Window manipulations

Here are the various locations for Window manipulations in the Gnome registry and their purposes. To edit these, you’ll have to have the gconf-editor installed.

• /apps/metacity/window_keybindings/maximize
  Maximize the window. Disable this setting because it doesn’t “toggle” the maximization state, it only maximizes the window. Just edit the value and enter ‘disabled‘ as the value.
• /apps/metacity/window_keybindings/maximize_horizontally
  Maximize the window horizontally. (make it as wide as the screen while keeping the same height)
• /apps/metacity/window_keybindings/maximize_vertically
  Maximize the window vertically. (make it as high as the screen while keeping the same width)
• /apps/metacity/window_keybindings/toggle_maximized
  Maximize the window on the first keypress. Unmaximize it on the next keypress.
• /apps/metacity/window_keybindings/toggle_shaded
  Roll up the window so that only the title bar is visible. This is handy for quickly peaking under the currently focussed window.

You can edit these bindings by right-clicking on the key and selecting ‘Edit key’. For the value, you’ll have to type out the full keybinding name. For instance: “<Control><Alt>r” (without the quotes). Take a look at the already defined keybindings for hints.

Global command-running keybindings

After finding out about the above configuration options for Metacity, I took a closer look at other options, and it turns out you can also bind global keybindings to programs so you can have shortcuts. Just press the keybinding and the program starts. I’m using this mostly for the top-10 applications I use: browser, editor, terminal emulator and some other stuff. Here’s how to add keybindings to programs:

1. In gconf-editor, find the key /apps/metacity/keybinding_commands/. Here, you’ll see a list of ‘command_NR’ key/value pairs.
2. Edit the value for one of the command_NR keys, and enter the name of the program you want to run when pressing some keybinding. For instance: /usr/bin/gvim
3. Now, go to /apps/metacity/global_keybindings/. Here, you’ll see a list of keys with names similar to run_command_NR.
4. Edit the value for the key with the name corresponding to the key you edited in step 2. Enter your keybinding in the same way as mentioned above.

Using the Windows key for bindings

Perhaps it’s not the same on every system, but I couldn’t use the Windows key (left of the left Alt key) for keybindings. When I tried binding commands to it in Gnome’s Keyboard Shortcuts manager, all I got was an ‘Super_L’ entry, and I couldn’t enter any extra modifiers (such as <Super>e, to run my Editor). Turns out you have to change the behaviour of the Win key so that it registers as a normal modifier key (similar to Shift, Control, etc) in X.org. Here’s how to do that:

1. Open the Keyboard manager. On my system, it’s the System → Preferences → Keyboard menu-option.
2. Open the Layout options tab.
3. Open the Alt/Win key behavior fold-out.
4. Choose the Meta is mapped to the left Win-key option.
5. Now, Meta is a code-name for one of the modifier-keys. Each modifier key (Shift, Alt, Control, etc) has a codename. But internally, X.org doesn't use these codenames. Instead, it used different names: Mod1 through Mod5. And apparently it differs from system to system to which Mod-X internal name the Meta modifier is mapped. So in order to find out which Mod-X you'll need to use when specifying keybindings, you can use the Gnome Keyboard Shortcuts manager.
6. Open the Gnome Keyboard Shortcuts manager. (System → Preferences → Keyboard shortcuts)
7. Click on of the options, and press the Win key with some other key. This will appear in the manager as: l, for instance. You now know that you need to use Mod4 if you want to bind commands or other things to the Win key when using the GConf-editor tool.