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