laravel5.5源码笔记（八、Eloquent ORM）

上一篇写到Eloquent ORM的基类Builder类，这次就来看一下这些方便的ORM方法是如何转换成sql语句运行的。

首先还是进入\vendor\laravel\framework\src\Illuminate\Database\Query\Builder.php这个类中，先来看一下最常用的where()方法。

如下所示，where方法的代码很长，但前面多个if都是用来兼容各种不同调用式的。我们先抛开这些花哨的调用方式，来看一下最简单的调用方法是怎么运行的。

 /**
      * Add a basic where clause to the query.
      *
      * @param  string|array|\Closure  $column
      * @param  mixed   $operator
      * @param  mixed   $value
      * @param  string  $boolean
      * @return $this
      */
     public function where($column, $operator = null, $value = null, $boolean = 'and')
     {
         // If the column is an array, we will assume it is an array of key-value pairs
         // and can add them each as a where clause. We will maintain the boolean we
         // received when the method was called and pass it into the nested where.
         if (is_array($column)) {
             return $this->addArrayOfWheres($column, $boolean);
         }
 
         // Here we will make some assumptions about the operator. If only 2 values are
         // passed to the method, we will assume that the operator is an equals sign
         // and keep going. Otherwise, we'll require the operator to be passed in.
         list($value, $operator) = $this->prepareValueAndOperator(
             $value, $operator, func_num_args() == 2
         );
 
         // If the columns is actually a Closure instance, we will assume the developer
         // wants to begin a nested where statement which is wrapped in parenthesis.
         // We'll add that Closure to the query then return back out immediately.
         if ($column instanceof Closure) {
             return $this->whereNested($column, $boolean);
         }
 
         // If the given operator is not found in the list of valid operators we will
         // assume that the developer is just short-cutting the '=' operators and
         // we will set the operators to '=' and set the values appropriately.
         if ($this->invalidOperator($operator)) {
             list($value, $operator) = [$operator, '='];
         }
 
         // If the value is a Closure, it means the developer is performing an entire
         // sub-select within the query and we will need to compile the sub-select
         // within the where clause to get the appropriate query record results.
         if ($value instanceof Closure) {
             return $this->whereSub($column, $operator, $value, $boolean);
         }
 
         // If the value is "null", we will just assume the developer wants to add a
         // where null clause to the query. So, we will allow a short-cut here to
         // that method for convenience so the developer doesn't have to check.
         if (is_null($value)) {
             return $this->whereNull($column, $boolean, $operator !== '=');
         }
 
         // If the column is making a JSON reference we'll check to see if the value
         // is a boolean. If it is, we'll add the raw boolean string as an actual
         // value to the query to ensure this is properly handled by the query.
         if (Str::contains($column, '->') && is_bool($value)) {
             $value = new Expression($value ? 'true' : 'false');
         }
 
         // Now that we are working with just a simple query we can put the elements
         // in our array and add the query binding to our array of bindings that
         // will be bound to each SQL statements when it is finally executed.
         $type = 'Basic';
 
         $this->wheres[] = compact(
             'type', 'column', 'operator', 'value', 'boolean'
         );
 
         if (! $value instanceof Expression) {
             $this->addBinding($value, 'where');
         }
 
         return $this;
     }

先从这个方法的参数开始，它一共有4个形参，分别代表$column字段、$operator操作符、$value值、$boolean = 'and'。

从字面意思我们可以猜测到，最原始的where方法，一开始是打算像$model->where('age', '>', 18)->get()这样来进行基本查询操作的。

那么让我们先抛开前面那些if代码块，直接跳到方法底部builder类通过compact函数，将基础参数添加到$this->wheres数组后，在判断$value不是一个表达式后，跳转到了addBinding方法中。

     public function addBinding($value, $type = 'where')
     {
 
         if (! array_key_exists($type, $this->bindings)) {
             throw new InvalidArgumentException("Invalid binding type: {$type}.");
         }
 
         if (is_array($value)) {
             $this->bindings[$type] = array_values(array_merge($this->bindings[$type], $value));
         } else {
             $this->bindings[$type][] = $value;
         }
 
         return $this;
     }

接下来看addBinding方法做了什么，首先一次array_key_exists校验确定传入条件正确。然后判断传入的value是否为数组，若非数组，则直接将这个值传入$this->bindings数组的对应操作中。打印出来如下所示。

随后便直接返回了$this对象，一个最简单的where方法就执行完毕了。

那么，按正常操作，接下来就改执行get()方法了。

     public function get($columns = ['*'])
     {
         $original = $this->columns;
 
         if (is_null($original)) {
             $this->columns = $columns;
         }
 
         $results = $this->processor->processSelect($this, $this->runSelect());
 
         $this->columns = $original;
 
         return collect($results);
     }

这个方法首先获取了要查询的字段，若为空则使用传入方法的$columns参数。然后通过$this->runSelect()方法进行查询，通过processor将返回值包装返回。

让我们来看一下runSelect()方法，这里的$this->connection其实是获取到pdo的链接对象，select()方法的三个参数分别为sql语句，pdo为了防注入将语句与值给分开了，所以第二个参数为值，第三个参数则是为了通过参数获取只读或读写模式的pdo实例。

getBindings()直接从对象中获取数据，并通过laravel 的 Arr对象进行包装。

而toSql()方法想要获得sql语句却没有那么简单，它需要调用多个方法来对sql进行拼接。

    protected function runSelect()
    {
        return $this->connection->select(
            $this->toSql(), $this->getBindings(), ! $this->useWritePdo
        );
    }
 
    public function getBindings()
    {
        return Arr::flatten($this->bindings);
    }
 
    public function toSql()
    {
        return $this->grammar->compileSelect($this);
    }

那么现在来看一下sql语句是如何获取到的吧。compileSelect方法位于\vendor\laravel\framework\src\Illuminate\Database\Query\Grammars\Grammar.php对象中，它会通过Builder对象中的属性数据，来拼接一条sql返回出去。

    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.
        $sql = trim($this->concatenate(
            $this->compileComponents($query))
        );
 
        $query->columns = $original;
 
        return $sql;
    }

这个方法一开始获取了语句要查询的字段。并做了空值判断，若为空则查询 * 。

接下来我们看一下$this->compileComponents($query)这一句代码，它的作用是返回基本的sql语句段，返回值如下所示。

然后通过$this->concatenate()方法将其拼接成一条完整的sql语句。为了搞清楚sql语句是怎么来的，我们又得深入compileComponents方法了。

这个方法位于\vendor\laravel\framework\src\Illuminate\Database\Query\Grammars\Grammar.php对象内部。先来看一下它的代码。

    protected function compileComponents(Builder $query)
    {
        $sql = [];
 
        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);
                //var_dump($component,$method,$query->$component,'-------'); //将这些条件打印出来看一下
                $sql[$component] = $this->$method($query, $query->$component);
            }
        }
        //dd('over');
        return $sql;
    }

这个方法内部，将selectComponents属性，也就是查询语句模板，进行了遍历，并判断出了，在$query对象中所存在的那一部分。通过这些语句，来构建sql语句片段。这个模板如下所示。

    protected $selectComponents = [
        'aggregate',
        'columns',
        'from',
        'joins',
        'wheres',
        'groups',
        'havings',
        'orders',
        'limit',
        'offset',
        'unions',
        'lock',
    ];

而$query对象中所存在的部分，将它们打印后，结果如下所示。通过我上面代码段中被注释的部分，将其打印了出来，我在下图中对三个属性做了注释。

总结来讲，这个方法会根据builder对象中所存储的属性，运行模板方法，将其构建成sql字符串部件。而builder对象中的属性则是我们自己通过DB或Model方法添加进去的。

那么我们刚刚那句简单的sql查询则是运行了compileColumns、compileFrom、compileWheres。这三个方法。

    protected function compileColumns(Builder $query, $columns)
    {
        // If the query is actually performing an aggregating select, we will let that
        // compiler handle the building of the select clauses, as it will need some
        // more syntax that is best handled by that function to keep things neat.
        if (! is_null($query->aggregate)) {
            return;
        }
 
        $select = $query->distinct ? 'select distinct ' : 'select ';
 
        return $select.$this->columnize($columns);
    }
 
    public function columnize(array $columns)
    {
        return implode(', ', array_map([$this, 'wrap'], $columns));
    }

先来看compileColumns，这个方法看上去很简单，判断aggregate不为空后，根据distinct 属性来得出sql语句头，然后将这个字符串与$this->columnize()方法的返回值进行拼接。就得出了上面'select *'这句字符串。而关键在于columnize方法中的array_map的[$this, 'wrap']。

array_map这个函数会传入两个参数，第一个参数为函数名，第二个参数为数组。将第二个数组参数中的每个值当成参数，传入第一个参数所代表的函数中循环执行。

那么现在我们要找到wrap这个方法了。

    public function wrap($value, $prefixAlias = false)
    {
        if ($this->isExpression($value)) {
            return $this->getValue($value);
        }
 
        // If the value being wrapped has a column alias we will need to separate out
        // the pieces so we can wrap each of the segments of the expression on it
        // own, and then joins them both back together with the "as" connector.
        if (strpos(strtolower($value), ' as ') !== false) {
            return $this->wrapAliasedValue($value, $prefixAlias);
        }
 
        return $this->wrapSegments(explode('.', $value));
    }

这个方法，首先判断了传入参数不是一个表达式，而是一个确定的值。然后strpos(strtolower($value), ' as ') !== false这一句将$value转为小写，并判断了sql语句中没有as字段。然后便返回了$this->wrapSegments的值。

    protected function wrapSegments($segments)
    {
        return collect($segments)->map(function ($segment, $key) use ($segments) {
            return $key == 0 && count($segments) > 1
                            ? $this->wrapTable($segment)
                            : $this->wrapValue($segment);
        })->implode('.');
    }

到这里，我们会发现这个方法，只是传入了一个闭包函数，就给返回了，laravel框架实在是难以跟踪。

事实上collect()方法代表了\vendor\laravel\framework\src\Illuminate\Support\Collection.php对象。

可以看到在collection类的构造方法中，我们将参数存入了它的属性，而在map方法中，通过array_keys对这些属性做了处理过后，又通过array_map对其进了加工。看下刚刚wrapSegments中的闭包函数是怎么写的，他们调用了wrapTable()和wrapValue这两个方法。根据传入参数的不同，来分别调用。

    public function __construct($items = [])
    {
        $this->items = $this->getArrayableItems($items);
    }
 
    public function map(callable $callback)
    {
        $keys = array_keys($this->items);
 
        $items = array_map($callback, $this->items, $keys);
 
        return new static(array_combine($keys, $items));
    }

    protected function wrapValue($value)
    {
        if ($value !== '*') {
            return '"'.str_replace('"', '""', $value).'"';
        }
 
        return $value;
    }

如果参数为*则直接返回了拼接星号的字符串，反之则直接返回了$value数组。然后视线调回collection对象的map方法，返回值在通过array_combine函数加工后，又通过collection本类包装成了对象返回。到这里函数调用就到顶了，依次返回值，返回到Grammars对象的compileColumns方法中，与'select'字符串进行拼接后再次返回。这部分sql语句片段就构建完成了。

那么接下来就剩compileFrom、compileWheres两个方法了。

    protected function compileFrom(Builder $query, $table)
    {
        return 'from '.$this->wrapTable($table);
    }
 
    public function wrapTable($table)
    {
        if (! $this->isExpression($table)) {
            return $this->wrap($this->tablePrefix.$table, true);
        }
 
        return $this->getValue($table);
    }

from语句的构建比较简单，直接from接表名就好。但是wrapTable方法中的代码我们发现有点眼熟，没错，它又调用了wrap方法，还记得我们刚刚构建select时看到的吗？这个方法只是对传入的参数做了解析，并包装成集合返回回来。其实不止select和from其他的语句段构建都要通过wrap方法来进行参数解析。刚刚已经解析过wrap方法，这里我就不多说了。最后，这个方法也是返回了'from'部分的sql语句片段。

接下来到compileWheres方法了。

    protected function compileWheres(Builder $query)
    {
        // Each type of where clauses has its own compiler function which is responsible
        // for actually creating the where clauses SQL. This helps keep the code nice
        // and maintainable since each clause has a very small method that it uses.
        if (is_null($query->wheres)) {
            return '';
        }
 
        // If we actually have some where clauses, we will strip off the first boolean
        // operator, which is added by the query builders for convenience so we can
        // avoid checking for the first clauses in each of the compilers methods.
        if (count($sql = $this->compileWheresToArray($query)) > 0) {
            return $this->concatenateWhereClauses($query, $sql);
        }
 
        return '';
    }
 
    protected function compileWheresToArray($query)
    {
        return collect($query->wheres)->map(function ($where) use ($query) {
            return $where['boolean'].' '.$this->{"where{$where['type']}"}($query, $where);
        })->all();
    }
 
    protected function concatenateWhereClauses($query, $sql)
    {
        $conjunction = $query instanceof JoinClause ? 'on' : 'where';
 
        return $conjunction.' '.$this->removeLeadingBoolean(implode(' ', $sql));
    }
 
    protected function removeLeadingBoolean($value)
    {
        return preg_replace('/and |or /i', '', $value, 1);
    }

那么，来看一下。首先compileWheres方法判断where条件是否为空，然后compileWheresToArray方法来判断where参数是否大于0。这个方法用了collect对象的map方法，我们之前已经看过了。重要的是这个闭包函数，来看一下这个闭包函数干了什么。它通过$hwere['type']这个属性中存储的字段作为方法名调用了whereBasic方法，如下所示

    protected function whereBasic(Builder $query, $where)
    {
        $value = $this->parameter($where['value']);
 
        return $this->wrap($where['column']).' '.$where['operator'].' '.$value;
    }

    public function parameter($value)
    {
        return $this->isExpression($value) ? $this->getValue($value) : '?';
    }

通过parameter方法获取到参数后，依然是通过wrap包装参数。concatenateWhereClauses方法根据之前返回的参数，决定拼接'where'字符串，然后通过removeLeadingBoolean方法决定‘and‘等条件的拼接。

到这里，基础sql语句片段就已经全部构建出来了。

视线跳回compileSelect方法的concatenate方法。

    protected function concatenate($segments)
    {
        return implode(' ', array_filter($segments, function ($value) {
            return (string) $value !== '';
        }));
    }

通过array_filter与implode函数将sql语句片段合并为了一条完整sql语句。

sql语句有了，我们视线又要跳回Builder对象的runSelect方法了。这个里面的$this->connection->select()方法对sql进行了调用，返回的便是查询结果了。connection则是Illuminate\Database\MySqlConnection对象。

    protected function runSelect()
    {
        return $this->connection->select(
            $this->toSql(), $this->getBindings(), ! $this->useWritePdo
        );
    }

而select方法则是在它的父类\vendor\laravel\framework\src\Illuminate\Database\Connection.php中。

    public function select($query, $bindings = [], $useReadPdo = true)
    {
        return $this->run($query, $bindings, function ($query, $bindings) use ($useReadPdo) {
            if ($this->pretending()) {
                return [];
            }
 
            // For select statements, we'll simply execute the query and return an array
            // of the database result set. Each element in the array will be a single
            // row from the database table, and will either be an array or objects.
            $statement = $this->prepared($this->getPdoForSelect($useReadPdo)
                              ->prepare($query));
 
            $this->bindValues($statement, $this->prepareBindings($bindings));
 
            $statement->execute();
 
            return $statement->fetchAll();
        });
    }
 
    protected function run($query, $bindings, Closure $callback)
    {
        $this->reconnectIfMissingConnection();
 
        $start = microtime(true);
 
        // Here we will run this query. If an exception occurs we'll determine if it was
        // caused by a connection that has been lost. If that is the cause, we'll try
        // to re-establish connection and re-run the query with a fresh connection.
        try {
            $result = $this->runQueryCallback($query, $bindings, $callback);
        } catch (QueryException $e) {
            $result = $this->handleQueryException(
                $e, $query, $bindings, $callback
            );
        }
 
        // Once we have run the query we will calculate the time that it took to run and
        // then log the query, bindings, and execution time so we will report them on
        // the event that the developer needs them. We'll log time in milliseconds.
        $this->logQuery(
            $query, $bindings, $this->getElapsedTime($start)
        );
 
        return $result;
    }
 
    protected function runQueryCallback($query, $bindings, Closure $callback)
    {
        // To execute the statement, we'll simply call the callback, which will actually
        // run the SQL against the PDO connection. Then we can calculate the time it
        // took to execute and log the query SQL, bindings and time in our memory.
        try {
            $result = $callback($query, $bindings);
        }
 
        // If an exception occurs when attempting to run a query, we'll format the error
        // message to include the bindings with SQL, which will make this exception a
        // lot more helpful to the developer instead of just the database's errors.
        catch (Exception $e) {
            throw new QueryException(
                $query, $this->prepareBindings($bindings), $e
            );
        }
 
        return $result;
    }

这三个方法，看起来很长一段，但是其中的代码是很简单的。我们一个一个来分析，select方法，只做了一件事，调用run方法，把sql语句，bindings参数，以及一个闭包函数传入了其中。

而run方法，则是获取了pdo链接，记录了开始查询的毫秒时间，通过runQueryCallback运行了查询闭包函数，并记录sql日志，最后返回了查询结果。

runQueryCallback方法只是简单的调用了闭包函数。现在转回来看闭包函数做了什么。

            $statement = $this->prepared($this->getPdoForSelect($useReadPdo)
                              ->prepare($query));
 
            $this->bindValues($statement, $this->prepareBindings($bindings));

关键代码就是这两句了。$this->getPdoForSelect($useReadPdo)方法通过之前设置的读写方式获取pdo实例。这里做了这么多判断，最终获取到的是provider初始化时存入的实例

    protected function getPdoForSelect($useReadPdo = true)
    {
        return $useReadPdo ? $this->getReadPdo() : $this->getPdo();
    }
 
    public function getReadPdo()
    {
        if ($this->transactions > 0) {
            return $this->getPdo();
        }
 
        if ($this->getConfig('sticky') && $this->recordsModified) {
            return $this->getPdo();
        }
 
        if ($this->readPdo instanceof Closure) {
            return $this->readPdo = call_user_func($this->readPdo);
        }
 
        return $this->readPdo ?: $this->getPdo();
    }

获取到pdo对象后，剩下的都是pdo的原生方法了。fetchAll方法返回sql查询结果集。

然后一直返回到get()方法。

    public function get($columns = ['*'])
    {
        $original = $this->columns;
 
        if (is_null($original)) {
            $this->columns = $columns;
        }
 
        $results = $this->processor->processSelect($this, $this->runSelect());
 
        $this->columns = $original;
 
        return collect($results);
    }

到这里，通过collect集合进行包装之后，便返回到我们model对象的操作方式了。