laravel框架model类查询实现：
User::where(['uid'=8])->get();
User类继承自Model类：Illuminate\Database\Eloquent\Model
当User类静态调用where方法时，自动调用了Model里的魔术方法：
public static function __callStatic($method, $parameters)
{
$instance = new static; //这里的$instance就是User类的实例对象
return call_user_func_array([$instance, $method], $parameters);
}
相当于调用了user对象的where方法，这时就又调用了魔术方法：
public function __call($method, $parameters)
{
if (in_array($method, ['increment', 'decrement'])) {
return call_user_func_array([$this, $method], $parameters);
}
$query = $this->newQuery(); //返回Illuminate\Database\Eloquent\Builder对象
return call_user_func_array([$query, $method], $parameters);
}
相当于调用Illuminate\Database\Eloquent\Builder对象里的where方法和get方法，这两个方法里其实
其实是封装调用了Illuminate\Database\Query\Builder对象里的where方法和get方法->get方法里调用了runselect方法
runSelect方法:
/**
* Run the query as a "select" statement against the connection.
*
* @return array
*/
protected function runSelect()
{
return $this->connection->select($this->toSql(), $this->getBindings(), ! $this->useWritePdo); //调用connection 对象的select方法
}
再看connection对象是怎么传到Illuminate\Database\Eloquent\Builder类实例里的：
Model类的newQuery方法：
/**
* Get a new query builder for the model's table.
*
* @return \Illuminate\Database\Eloquent\Builder
*/
public function newQuery()
{
$builder = $this->newQueryWithoutScopes();
return $this->applyGlobalScopes($builder);
}
Model类的newQueryWithoutScopes方法：
/**
* Get a new query builder that doesn't have any global scopes.
*
* @return \Illuminate\Database\Eloquent\Builder|static
*/
public function newQueryWithoutScopes()
{
$builder = $this->newEloquentBuilder(
$this->newBaseQueryBuilder() //这个方法返回
);
// Once we have the query builders, we will set the model instances so the
// builder can easily access any information it may need from the model
// while it is constructing and executing various queries against it.
return $builder->setModel($this)->with($this->with);
}
Model类的newBaseQueryBuilder方法实现
/**
* Get a new query builder instance for the connection.
*
* @return \Illuminate\Database\Query\Builder
*/
protected function newBaseQueryBuilder()
{
$conn = $this->getConnection(); \\连接数据库并返回connection对象
$grammar = $conn->getQueryGrammar();
return new QueryBuilder($conn, $grammar, $conn->getPostProcessor()); //Illuminate\Database\Query\Builder
}
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