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Add another simple example, add sidebar.rst and reorganize content a …
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DQL Lexer | ||
========= | ||
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||
Here is a more complicated example from the Doctrine ORM project. | ||
The ``Doctrine\ORM\Query\Lexer`` implementation for DQL looks something | ||
like the following: | ||
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||
.. code-block:: php | ||
use Doctrine\Common\Lexer\AbstractLexer; | ||
class Lexer extends AbstractLexer | ||
{ | ||
// All tokens that are not valid identifiers must be < 100 | ||
public const T_NONE = 1; | ||
public const T_INTEGER = 2; | ||
public const T_STRING = 3; | ||
public const T_INPUT_PARAMETER = 4; | ||
public const T_FLOAT = 5; | ||
public const T_CLOSE_PARENTHESIS = 6; | ||
public const T_OPEN_PARENTHESIS = 7; | ||
public const T_COMMA = 8; | ||
public const T_DIVIDE = 9; | ||
public const T_DOT = 10; | ||
public const T_EQUALS = 11; | ||
public const T_GREATER_THAN = 12; | ||
public const T_LOWER_THAN = 13; | ||
public const T_MINUS = 14; | ||
public const T_MULTIPLY = 15; | ||
public const T_NEGATE = 16; | ||
public const T_PLUS = 17; | ||
public const T_OPEN_CURLY_BRACE = 18; | ||
public const T_CLOSE_CURLY_BRACE = 19; | ||
// All tokens that are identifiers or keywords that could be considered as identifiers should be >= 100 | ||
public const T_ALIASED_NAME = 100; | ||
public const T_FULLY_QUALIFIED_NAME = 101; | ||
public const T_IDENTIFIER = 102; | ||
// All keyword tokens should be >= 200 | ||
public const T_ALL = 200; | ||
public const T_AND = 201; | ||
public const T_ANY = 202; | ||
public const T_AS = 203; | ||
public const T_ASC = 204; | ||
public const T_AVG = 205; | ||
public const T_BETWEEN = 206; | ||
public const T_BOTH = 207; | ||
public const T_BY = 208; | ||
public const T_CASE = 209; | ||
public const T_COALESCE = 210; | ||
public const T_COUNT = 211; | ||
public const T_DELETE = 212; | ||
public const T_DESC = 213; | ||
public const T_DISTINCT = 214; | ||
public const T_ELSE = 215; | ||
public const T_EMPTY = 216; | ||
public const T_END = 217; | ||
public const T_ESCAPE = 218; | ||
public const T_EXISTS = 219; | ||
public const T_FALSE = 220; | ||
public const T_FROM = 221; | ||
public const T_GROUP = 222; | ||
public const T_HAVING = 223; | ||
public const T_HIDDEN = 224; | ||
public const T_IN = 225; | ||
public const T_INDEX = 226; | ||
public const T_INNER = 227; | ||
public const T_INSTANCE = 228; | ||
public const T_IS = 229; | ||
public const T_JOIN = 230; | ||
public const T_LEADING = 231; | ||
public const T_LEFT = 232; | ||
public const T_LIKE = 233; | ||
public const T_MAX = 234; | ||
public const T_MEMBER = 235; | ||
public const T_MIN = 236; | ||
public const T_NEW = 237; | ||
public const T_NOT = 238; | ||
public const T_NULL = 239; | ||
public const T_NULLIF = 240; | ||
public const T_OF = 241; | ||
public const T_OR = 242; | ||
public const T_ORDER = 243; | ||
public const T_OUTER = 244; | ||
public const T_PARTIAL = 245; | ||
public const T_SELECT = 246; | ||
public const T_SET = 247; | ||
public const T_SOME = 248; | ||
public const T_SUM = 249; | ||
public const T_THEN = 250; | ||
public const T_TRAILING = 251; | ||
public const T_TRUE = 252; | ||
public const T_UPDATE = 253; | ||
public const T_WHEN = 254; | ||
public const T_WHERE = 255; | ||
public const T_WITH = 256; | ||
/** | ||
* Creates a new query scanner object. | ||
* | ||
* @param string $input A query string. | ||
*/ | ||
public function __construct($input) | ||
{ | ||
$this->setInput($input); | ||
} | ||
/** | ||
* {@inheritdoc} | ||
*/ | ||
protected function getCatchablePatterns() | ||
{ | ||
return [ | ||
'[a-z_][a-z0-9_]*\:[a-z_][a-z0-9_]*(?:\\\[a-z_][a-z0-9_]*)*', // aliased name | ||
'[a-z_\\\][a-z0-9_]*(?:\\\[a-z_][a-z0-9_]*)*', // identifier or qualified name | ||
'(?:[0-9]+(?:[\.][0-9]+)*)(?:e[+-]?[0-9]+)?', // numbers | ||
"'(?:[^']|'')*'", // quoted strings | ||
'\?[0-9]*|:[a-z_][a-z0-9_]*', // parameters | ||
]; | ||
} | ||
/** | ||
* {@inheritdoc} | ||
*/ | ||
protected function getNonCatchablePatterns() | ||
{ | ||
return ['\s+', '(.)']; | ||
} | ||
/** | ||
* {@inheritdoc} | ||
*/ | ||
protected function getType(&$value) | ||
{ | ||
$type = self::T_NONE; | ||
switch (true) { | ||
// Recognize numeric values | ||
case (is_numeric($value)): | ||
if (strpos($value, '.') !== false || stripos($value, 'e') !== false) { | ||
return self::T_FLOAT; | ||
} | ||
return self::T_INTEGER; | ||
// Recognize quoted strings | ||
case ($value[0] === "'"): | ||
$value = str_replace("''", "'", substr($value, 1, strlen($value) - 2)); | ||
return self::T_STRING; | ||
// Recognize identifiers, aliased or qualified names | ||
case (ctype_alpha($value[0]) || $value[0] === '_' || $value[0] === '\\'): | ||
$name = 'Doctrine\ORM\Query\Lexer::T_' . strtoupper($value); | ||
if (defined($name)) { | ||
$type = constant($name); | ||
if ($type > 100) { | ||
return $type; | ||
} | ||
} | ||
if (strpos($value, ':') !== false) { | ||
return self::T_ALIASED_NAME; | ||
} | ||
if (strpos($value, '\\') !== false) { | ||
return self::T_FULLY_QUALIFIED_NAME; | ||
} | ||
return self::T_IDENTIFIER; | ||
// Recognize input parameters | ||
case ($value[0] === '?' || $value[0] === ':'): | ||
return self::T_INPUT_PARAMETER; | ||
// Recognize symbols | ||
case ($value === '.'): | ||
return self::T_DOT; | ||
case ($value === ','): | ||
return self::T_COMMA; | ||
case ($value === '('): | ||
return self::T_OPEN_PARENTHESIS; | ||
case ($value === ')'): | ||
return self::T_CLOSE_PARENTHESIS; | ||
case ($value === '='): | ||
return self::T_EQUALS; | ||
case ($value === '>'): | ||
return self::T_GREATER_THAN; | ||
case ($value === '<'): | ||
return self::T_LOWER_THAN; | ||
case ($value === '+'): | ||
return self::T_PLUS; | ||
case ($value === '-'): | ||
return self::T_MINUS; | ||
case ($value === '*'): | ||
return self::T_MULTIPLY; | ||
case ($value === '/'): | ||
return self::T_DIVIDE; | ||
case ($value === '!'): | ||
return self::T_NEGATE; | ||
case ($value === '{'): | ||
return self::T_OPEN_CURLY_BRACE; | ||
case ($value === '}'): | ||
return self::T_CLOSE_CURLY_BRACE; | ||
// Default | ||
default: | ||
// Do nothing | ||
} | ||
return $type; | ||
} | ||
} | ||
DQL Parser | ||
---------- | ||
|
||
This is roughly what the DQL Parser looks like that uses the above | ||
Lexer implementation: | ||
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.. note:: | ||
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You can see the full implementation `here <https://github.com/doctrine/doctrine2/blob/master/lib/Doctrine/ORM/Query/Parser.php>`_. | ||
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.. code-block:: php | ||
class Parser | ||
{ | ||
private $lexer; | ||
public function __construct($dql) | ||
{ | ||
$this->lexer = new Lexer(); | ||
$this->lexer->setInput($dql); | ||
} | ||
// ... | ||
public function getAST() | ||
{ | ||
// Parse & build AST | ||
$AST = $this->QueryLanguage(); | ||
// ... | ||
return $AST; | ||
} | ||
public function QueryLanguage() | ||
{ | ||
$this->lexer->moveNext(); | ||
switch ($this->lexer->lookahead['type']) { | ||
case Lexer::T_SELECT: | ||
$statement = $this->SelectStatement(); | ||
break; | ||
case Lexer::T_UPDATE: | ||
$statement = $this->UpdateStatement(); | ||
break; | ||
case Lexer::T_DELETE: | ||
$statement = $this->DeleteStatement(); | ||
break; | ||
default: | ||
$this->syntaxError('SELECT, UPDATE or DELETE'); | ||
break; | ||
} | ||
// Check for end of string | ||
if ($this->lexer->lookahead !== null) { | ||
$this->syntaxError('end of string'); | ||
} | ||
return $statement; | ||
} | ||
// ... | ||
} | ||
Now the AST is used to transform the DQL query in to portable SQL for whatever relational | ||
database you are using! | ||
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.. code-block:: php | ||
$parser = new Parser('SELECT u FROM User u'); | ||
$AST = $parser->getAST(); // returns \Doctrine\ORM\Query\AST\SelectStatement | ||
What is an AST? | ||
--------------- | ||
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||
AST stands for `Abstract syntax tree <http://en.wikipedia.org/wiki/Abstract_syntax_tree>`_. | ||
In computer science, an abstract syntax tree (AST), or just syntax tree, is a | ||
tree representation of the abstract syntactic structure of source code written | ||
in a programming language. Each node of the tree denotes a construct occurring in | ||
the source code. |
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