流接口模式（Fluent Interface）

1、模式定义

2、UML 类图

3、示例代码

Sql.php

<?php

namespace DesignPatterns\Structural\FluentInterface;

/**
 * SQL 类
 */
class Sql
{
    /**
     * @var array
     */
    protected $fields = array();

    /**
     * @var array
     */
    protected $from = array();

    /**
     * @var array
     */
    protected $where = array();

    /**
     * 添加 select 字段
     *
     * @param array $fields
     *
     * @return SQL
     */
    public function select(array $fields = array())
    {
        $this->fields = $fields;

        return $this;
    }

    /**
     * 添加 FROM 子句
     *
     * @param string $table
     * @param string $alias
     *
     * @return SQL
     */
    public function from($table, $alias)
    {
        $this->from[] = $table . ' AS ' . $alias;

        return $this;
    }

    /**
     * 添加 WHERE 条件
     *
     * @param string $condition
     *
     * @return SQL
     */
    public function where($condition)
    {
        $this->where[] = $condition;

        return $this;
    }

    /**
     * 生成查询语句
     *
     * @return string
     */
    public function getQuery()
    {
        return 'SELECT ' . implode(',', $this->fields)
                . ' FROM ' . implode(',', $this->from)
                . ' WHERE ' . implode(' AND ', $this->where);
    }
}

4、测试代码

Tests/FluentInterfaceTest.php

<?php

namespace DesignPatterns\Structural\FluentInterface\Tests;

use DesignPatterns\Structural\FluentInterface\Sql;

/**
 * FluentInterfaceTest 测试流接口SQL
 */
class FluentInterfaceTest extends \PHPUnit_Framework_TestCase
{

    public function testBuildSQL()
    {
        $instance = new Sql();
        $query = $instance->select(array('foo', 'bar'))
                ->from('foobar', 'f')
                ->where('f.bar = ?')
                ->getQuery();

        $this->assertEquals('SELECT foo,bar FROM foobar AS f WHERE f.bar = ?', $query);
    }
}