php中的流接口模式

概念

 流接口模式（Fluent Interface）用来编写易于阅读的代码，就像自然语言一样（如英语）

场景

Doctrine2 的 QueryBuilder，就像下面例子中类似
PHPUnit 使用连贯接口来创建 mock 对象
Yii 框架：CDbCommand 与 CActiveRecord 也使用此模式

示例

<?php

class Sql
{
    /**
     * @var array
     */
    private $fields = [];

    /**
     * @var array
     */
    private $from = [];

    /**
     * @var array
     */
    private $where = [];

    public function select(array $fields): Sql
    {
        $this->fields = $fields;

        return $this;
    }

    public function from(string $table, string $alias): Sql
    {
        $this->from[] = $table.' AS '.$alias;

        return $this;
    }

    public function where(string $condition): Sql
    {
        $this->where[] = $condition;

        return $this;
    }

    public function __toString(): string
    {
        return sprintf(
            'SELECT %s FROM %s WHERE %s',
            join(', ', $this->fields),
            join(', ', $this->from),
            join(' AND ', $this->where)
        );
    }
}