Active Record (AR) is a popular object-relational mapping (ORM) technology. Each AR class represents a data table (or view), the columns of the data table (or view) are reflected in the AR class as attributes of the class, and an AR instance represents a row in the table. Common CRUD operations are implemented as AR methods.

Therefore, we can access the data in a more object-oriented way. $c = new CDbCriteria(); is a way of writing ActiveRecord, which makes ActiveRecord more flexible, while assembling sql is the most common. Let’s look at two examples below. (Recommended learning: yii tutorial)

Note: AR is not intended to solve all database-related tasks. Its best applications are modeling data tables into PHP structures and executing queries that do not contain complex SQL statements. For complex query scenarios, Yii DAO should be used.

$criteria = new CDbCriteria;       
//函數(shù)方式 
$criteria->addCondition("id=1"); //查詢條件，即where id = 1   
$criteria->addInCondition('id', array(1,2,3,4,5)); //代表where id IN (1,23,,4,5,);   
$criteria->addNotInCondition('id', array(1,2,3,4,5));//與上面正好相法，是NOT IN   
$criteria->addCondition('id=1','OR');//這是OR條件，多個條件的時候，該條件是OR而非AND   
$criteria->addSearchCondition('name', '分類');//搜索條件，其實代表了。。where name like '%分類%'   
$criteria->addBetweenCondition('id', 1, 4);//between 1 and 4    
     
$criteria->compare('id', 1);    //這個方法比較特殊，他會根據(jù)你的參數(shù)自動處理成addCondition或者addInCondition，   
                                //即如果第二個參數(shù)是數(shù)組就會調(diào)用addInCondition   
$criteria->addCondition("id = :id");   
$criteria->params[':id']=1;   
      
//屬性方式   
$criteria->select = 'id,parentid,name'; //代表了要查詢的字段，默認select='*';   
$criteria->join = 'xxx'; //連接表   
$criteria->with = 'xxx'; //調(diào)用relations    
$criteria->limit = 10;    //取1條數(shù)據(jù)，如果小于0，則不作處理   
$criteria->offset = 1;   //兩條合并起來，則表示 limit 10 offset 1,或者代表了。limit 1,10   
$criteria->order = 'xxx DESC,XXX ASC' ;//排序條件   
$criteria->group = 'group 條件';   
$criteria->having = 'having 條件 ';   
$criteria->distinct = FALSE; //是否唯一查詢

Yii Data Access Object (DAO) is built on the PHP Data Object (PDO) extension, enabling access to different database management systems (DBMS) in a single unified interface . Applications developed using Yii's DAO can easily switch to use different database management systems without modifying the data access code. The following is an example of DAO:

Sample code

/**
     * 關(guān)于DAO的例子
     * 獲取所有用戶名
     */
    public function getUsernames ()
    {
        $sqlStatement = ' SELECT `username` FROM `testdrive`.`tbl_user` ';
        $this->command = $this->connection->createCommand($sqlStatement);
        return $this->command->queryAll();
    }
    /**
     *
     * 添加一個用戶
     */
    public function addUser ()
    {
        $sqlStatement = " INSERT INTO `tbl_user` (`username`, `password`, `email`) VALUES ('test', 'test', 'test@test.com') ";
        $this->command = $this->connection->createCommand($sqlStatement);
        return $this->command->execute();
    }

There are a few points to note:

1 , the difference from the DAO method is that each element in the DAO method array is still an array. With the CDbCriteria method, the elements in the array are objects.

2, even if this function is very powerful, there are still some requirements that cannot be met, and sql statements are still needed at this time. For example, select avg(num) amount from ****.

3, print the results after running, you can learn more about how Yii implements this

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