Laravel中tosql()是如何返回sql

前言

1. laravel version 5.5 

2. 关键字sql解析的代码，我就不上了。有兴趣的童鞋，可以去IlluminateDatabaseQueryGrammarsGrammar观望，我也就简单说下，Laravel的主体思路。

源码

首先找到tosql()方法所在的位置，IlluminateDatabaseQueryBuilder：

/**
     * Get the SQL representation of the query.
     *
     * @return string
     */
    public function toSql()
    {
        return $this->grammar->compileSelect($this);
    }

接着，去 IlluminateDatabaseQueryGrammarsGrammar

/**
     * The components that make up a select clause.
     *  关键字数组，用于下面的根据对应关键字拼接对应方法
     * @var array
     */
    protected $selectComponents = [
        'aggregate',
        'columns',
        'from',
        'joins',
        'wheres',
        'groups',
        'havings',
        'orders',
        'limit',
        'offset',
        'unions',
        'lock',
    ];

 /**
     * Compile a select query into SQL.
     *
     * @param  IlluminateDatabaseQueryBuilder  $query
     * @return string
     */
    public function compileSelect(Builder $query)
    {
        // If the query does not have any columns set, we'll set the columns to the
        // * character to just get all of the columns from the database. Then we
        // can build the query and concatenate all the pieces together as one.
        $original = $query->columns;

        if (is_null($query->columns)) {
            $query->columns = ['*'];
        }

        // To compile the query, we'll spin through each component of the query and
        // see if that component exists. If it does we'll just call the compiler
        // function for the component which is responsible for making the SQL.
　　　　　// 然鹅，最主体的方法就在这里。
        $sql = trim($this->concatenate(
            $this->compileComponents($query))
        );

        $query->columns = $original;

        return $sql;
    }
　　　　

 /**
     * Concatenate an array of segments, removing empties.
     *
     * @param  array   $segments
     * @return string
     */
    protected function concatenate($segments)
    {
　　　　　// 将空值过滤，并且转换为一个字符串，返回。（也就是最终返回的sql）
        return implode(' ', array_filter($segments, function ($value) {
            return (string) $value !== '';
        }));
    }

/**
     * Compile the components necessary for a select clause.
     *
     * @param  IlluminateDatabaseQueryBuilder  $query
     * @return array
     */
    protected function compileComponents(Builder $query)
    {
        $sql = [];
　　　　　// laravel 会根据sql的关键字，for循环出一个sql数组
        foreach ($this->selectComponents as $component) {
            // To compile the query, we'll spin through each component of the query and
            // see if that component exists. If it does we'll just call the compiler
            // function for the component which is responsible for making the SQL.
            if (! is_null($query->$component)) {
                $method = 'compile'.ucfirst($component);

                $sql[$component] = $this->$method($query, $query->$component);
            }
        }

        return $sql;
    }

总结

我个人也就是，简略的通过表象的源码分析下laravle的toSql()如何返回sql而已，尚未研究更为深透。

为什么开个博文来记录呢？因为，最近一直在看laravel的源码，觉得这种思想真的很新颖！！！

共勉~~~