通过模型关联操作把数据表的关联关系对象化，解决了大部分常用的关联场景，封装的关联操作比起常规的数据库联表操作更加智能和高效，并且直观。

避免在模型内部使用复杂的join查询和视图查询。

创建有关联的两个数据表

CREATE TABLE `article` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '文章id',
  `cateId` int(11) DEFAULT NULL COMMENT '文章分类id',
  `title` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL COMMENT '文章标题',
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=36 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

CREATE TABLE `category` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=29 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

创建article模型

namespace app\model;
use think\Model;
class Article extends Model
{
    //一篇文章只有一个分类，文章对分类是一对一
    public function category(){
        return $this->hasOne("Category","id","cateId");
    }
}

创建category模型

namespace app\model;
use think\Model;
class Category extends Model
{
   //一个分类可以有多篇文章，分类对文章是一对多
   public function article(){
       return $this->hasMany("article","cateId","id");
   }
}

控制器调用模型

namespace app\controller;
use app\model\Article;
use app\model\Category;
class Relation
{
    //关联查询-find
    public function find(){
        $article = Article::with('category')->where("id","=","2")->find();
        echo $article->title;
        // 输出category关联模型的name属性
        echo $article->category->name;
    }
    //关联查询-select
    public function select(){
        $article = Article::with('category')->select();
        foreach ($article as $user) {
            echo "<hr>";
            echo $user->category->name;
        }
    }
    //关联保存更新
    public function save(){
       $article = Article::with('category')->find(3);
        $article->save(['title'=>'这是第一篇文字']);
        $article->category()->save(['name' => '这是分类1']);
        //或者
        $article = Article::where("id","=","2")->find();
        $article->title = '更改标题1';
        $article->category->name = '更新内容1';
        // 更新当前模型及关联模型
        $article->together(['category'])->save();
    }

    //关联插入
    public function insert(){
        $blog = new Category;
        $blog->name = '分类标题';
        $content = new Article();
        $content->title = '文章标题';
        $blog->article = $content;
        $blog->together(["article"])->save();
    }
}