Yii多表联合查询操作详解

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            本文针对Yii多表联查进行汇总描述，供大家参考，具体内容如下
1、多表联查实现方法
有两种方式一种使用DAO写SQL语句实现，这种实现理解起来相对轻松，只要保证SQL语句不写错就行了。缺点也很明显，比较零散，而且不符合YII的推荐框架，最重要的缺点在于容易写错。
还有一种便是下面要说的使用YII自带的CActiveRecord实现多表联查
2、 整体框架
我们需要找到一个用户的好友关系，用户的信息放在用户表中，用户之间的关系放在关系表中，而关系的内容则放在关系类型表中。明显的我们只需要以关系表为主表联查其他两个表即可。我主要从代码的角度，分析下实现的过程。
3、CActiveRecord
我们首先需要对3张表建立相应的model，下面是关系表的代码
SocialRelation.php
true),
      // The following rule is used by search().
      // Please remove those attributes that should not be searched.
      array('relation_id, relation_type_id, user_id, another_user_id', 'safe', 'on'=>'search'),
    );
  }

  /**
   * @return array relational rules.
   */
  public function relations()
  {
    // NOTE: you may need to adjust the relation name and the related
    // class name for the relations automatically generated below.
    return array(
      'relationType' => array(self::BELONGS_TO, 'SocialRelationType', 'relation_type_id'),
      'user' => array(self::BELONGS_TO, 'AccessUser', 'user_id'),
      'anotherUser' => array(self::BELONGS_TO, 'AccessUser', 'another_user_id'),
    );
  }

  /**
   * @return array customized attribute labels (name=>label)
   */
  public function attributeLabels()
  {
    return array(
      'relation_id' => 'Relation',
      'relation_type_id' => 'Relation Type',
      'relation_type_name' => 'Relation Name',
      'user_id' => 'User ID',
      'user_name' => 'User Name',
      'another_user_id' => 'Another User',
      'another_user_name' => 'Another User Name',
    );
  }

  /**
   * Retrieves a list of models based on the current search/filter conditions.
   * @return CActiveDataProvider the data provider that can return the models based on the search/filter conditions.
   */
  public function search()
  {
    // Warning: Please modify the following code to remove attributes that
    // should not be searched.

    $criteria=new CDbCriteria;

    $criteria->compare('relation_id',$this->relation_id);
    $criteria->compare('relation_type_id',$this->relation_type_id);
    $criteria->compare('user_id',$this->user_id);
    $criteria->compare('another_user_id',$this->another_user_id);
    $criteria->with=array(
      'relationType',
    );

    return new CActiveDataProvider($this, array(
      'criteria'=>$criteria,
    ));
  }
}