How to make a symlink in Windows 7

1. open cmd (as an admin)
2. type:

mklink /d linkpath targetpath

example:

mklink /d c:\easytoremember c:\users\neil\local\applicationdata\temp\hardtoremember

on Database Trees

This is more a note to myself, but it looks like the best tree option in a database is Recursive Query, at least in Postgres, which supports the WITH clause.

Closure Table is the next best option.

Optimistic Concurrency Control with Yii's Activerecord

Here's how to do Optimistic Concurrency Control with Yii's ActiveRecord:

class OCCActiveRecord extends CActiveRecord{

  public $checksum = null;

  public function afterFind(){

    /* get a checksum of all the attribute values after reading a record from db */

    $this->checksum = md5(implode('', $this->getAttributes(false)));

    parent::afterFind();
  }

    public function rules(){

/* use an exist validator to make sure that a record with the same checksum is still in db. if it's been modified, then checksums will be different */

 return array(
     array('id', 'exist', 'message'=>'This record was modified after you read it', 'on'=>'update', 'criteria'=>array('condition'=>'md5(concat('.implode(',',$this->attributeNames()).'))=:checksum', 'params'=>array('checksum'=>$this->checksum)))
 );
    }

}

Just a rough sketch, but you get the idea.

You could also modify this to be a behavior. Works only with MySQL AFAIK.

Table Inheritance with Yii ActiveRecord

Need to use Table Inheritance with ActiveRecord? Here's how:

This is Single Table Inheritance only.

Imagine that you want People contacts and Organization contacts. You don't want to keep them in different tables, as sometimes you sell to people, and sometimes you sell to organizations, and you want to keep a single (foreign) key to the party that you sold to.

We will create a class called Party, with subtypes Person and Organization. They will share some of Party's rules and relationships.

Here is the database schema:

CREATE TABLE `tbl_party` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `type` char(1) NOT NULL comment 'p=person,o=organization',
 `name` varchar(255) NOT NULL comment 'surname if a person',
 `given_name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ;

and here is the model code:

class Party extends CActiveRecord {

    public static function model($className=__CLASS__){
 return parent::model($className);
    }

    public function tableName(){
 return 'tbl_party';
    }

    

    public function relations(){
 return array(
     
 );
    }

    public function rules(){
 return array(
     array('name,type','required'),
     array('type','in', 'range'=>array('o','p'))
 );
    }
}

class Person extends Party {

    /* this is required for subtypes */
    public static function model($className=__CLASS__){
 return parent::model($className);
    }

    public function defaultScope(){
        /* only read Parties that are People */
 return array(
     'condition'=>"type='p'"
 );
    }

    public function relations(){
        /* combine parent and own relations. can have 'People' only relations  */

 $parentRelations = parent::relations();

 $myRelations = array(

 );

 return array_merge($myRelations, $parentRelations);
    }

    public function rules(){
        /* combine parent and own rules */

 $parentRules = parent::rules();

 $myRules = array(
     array('type', 'default', 'value'=>'p'), /* set type to Person */
     array('type', 'in', 'range'=>array('p')), /* allow only Person type */
     array('given_name', 'required') /* new rule for this subtype only */
 );

 /* you want to apply parent rules last, delete them here if necessary */
 return array_merge($myRules, $parentRules);
    }

}

class Organization extends Party {

    public static function model($className=__CLASS__){
 return parent::model($className);
    }

    public function defaultScope(){
 return array(
     'condition'=>"type='o'"
 );
    }

    public function relations(){
 $parentRelations = parent::relations();

 $myRelations = array(
     
 );

 return array_merge($myRelations, $parentRelations);
    }

    public function rules(){
 $parentRules = parent::rules();

 $myRules = array(
     array('type', 'default', 'value'=>'o'),
     array('type', 'in', 'range'=>array('o'))
 );

 /* you want to apply parent rules last. delete them if necessary */
 return array_merge($myRules, $parentRules);
    }
}

Database Notes

Wanna build your schema online and share?

WW SQL Designer

Wanna test your SQL query online and share?

SQL Fiddle

This might come in handy for you, if you are struggling with a SQL query:

Common MySQL Queries

If you don't fully understand JOINs:

A Visual Explanation of SQL Joins

Wanna hot-backup your InnoDB database?

Percona XtraBackup (open source)

Need to recover a corrupt InnoDB table?

Percona Data Recovery Tool for InnoDB (open source)

Need to generate massive test data?

Benerator

Want to Validate your SQL?

Mimer SQL Validator

Random:

1. if you want decent full-text search, choose PostgreSQL over MySQL, as MySQL doesn't support free-text search at the same time as foreign keys and transactions.
2. Set your database to use the UTC timezone