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laravel5.5源码笔记(八、Eloquent ORM)

程序员文章站 2022-08-31 23:18:16
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w ......

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。

laravel5.5源码笔记(八、Eloquent ORM)
 1 /**
 2      * add a basic where clause to the query.
 3      *
 4      * @param  string|array|\closure  $column
 5      * @param  mixed   $operator
 6      * @param  mixed   $value
 7      * @param  string  $boolean
 8      * @return $this
 9      */
10     public function where($column, $operator = null, $value = null, $boolean = 'and')
11     {
12         // if the column is an array, we will assume it is an array of key-value pairs
13         // and can add them each as a where clause. we will maintain the boolean we
14         // received when the method was called and pass it into the nested where.
15         if (is_array($column)) {
16             return $this->addarrayofwheres($column, $boolean);
17         }
18 
19         // here we will make some assumptions about the operator. if only 2 values are
20         // passed to the method, we will assume that the operator is an equals sign
21         // and keep going. otherwise, we'll require the operator to be passed in.
22         list($value, $operator) = $this->preparevalueandoperator(
23             $value, $operator, func_num_args() == 2
24         );
25 
26         // if the columns is actually a closure instance, we will assume the developer
27         // wants to begin a nested where statement which is wrapped in parenthesis.
28         // we'll add that closure to the query then return back out immediately.
29         if ($column instanceof closure) {
30             return $this->wherenested($column, $boolean);
31         }
32 
33         // if the given operator is not found in the list of valid operators we will
34         // assume that the developer is just short-cutting the '=' operators and
35         // we will set the operators to '=' and set the values appropriately.
36         if ($this->invalidoperator($operator)) {
37             list($value, $operator) = [$operator, '='];
38         }
39 
40         // if the value is a closure, it means the developer is performing an entire
41         // sub-select within the query and we will need to compile the sub-select
42         // within the where clause to get the appropriate query record results.
43         if ($value instanceof closure) {
44             return $this->wheresub($column, $operator, $value, $boolean);
45         }
46 
47         // if the value is "null", we will just assume the developer wants to add a
48         // where null clause to the query. so, we will allow a short-cut here to
49         // that method for convenience so the developer doesn't have to check.
50         if (is_null($value)) {
51             return $this->wherenull($column, $boolean, $operator !== '=');
52         }
53 
54         // if the column is making a json reference we'll check to see if the value
55         // is a boolean. if it is, we'll add the raw boolean string as an actual
56         // value to the query to ensure this is properly handled by the query.
57         if (str::contains($column, '->') && is_bool($value)) {
58             $value = new expression($value ? 'true' : 'false');
59         }
60 
61         // now that we are working with just a simple query we can put the elements
62         // in our array and add the query binding to our array of bindings that
63         // will be bound to each sql statements when it is finally executed.
64         $type = 'basic';
65 
66         $this->wheres[] = compact(
67             'type', 'column', 'operator', 'value', 'boolean'
68         );
69 
70         if (! $value instanceof expression) {
71             $this->addbinding($value, 'where');
72         }
73 
74         return $this;
75     }
view code

 

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。

 

 1     public function addbinding($value, $type = 'where')
 2     {
 3 
 4         if (! array_key_exists($type, $this->bindings)) {
 5             throw new invalidargumentexception("invalid binding type: {$type}.");
 6         }
 7 
 8         if (is_array($value)) {
 9             $this->bindings[$type] = array_values(array_merge($this->bindings[$type], $value));
10         } else {
11             $this->bindings[$type][] = $value;
12         }
13 
14         return $this;
15     }

 

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。

laravel5.5源码笔记(八、Eloquent ORM)

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。

 1     public function get($columns = ['*'])
 2     {
 3         $original = $this->columns;
 4 
 5         if (is_null($original)) {
 6             $this->columns = $columns;
 7         }
 8 
 9         $results = $this->processor->processselect($this, $this->runselect());
10 
11         $this->columns = $original;
12 
13         return collect($results);
14     }

 

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。

laravel5.5源码笔记(八、Eloquent ORM)

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。

laravel5.5源码笔记(八、Eloquent ORM)

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。

laravel5.5源码笔记(八、Eloquent ORM)

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。