ExpressionVisitor

class ExpressionVisitor

An Expression visitor walks a graph of expressions and turns them into a query for the underlying implementation.

Methods

Details

Source code

<?php
/*
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * This software consists of voluntary contributions made by many individuals
 * and is licensed under the MIT license. For more information, see
 * <http://www.doctrine-project.org>.
 */

namespace Doctrine\Common\Collections\Expr;

/**
 * An Expression visitor walks a graph of expressions and turns them into a
 * query for the underlying implementation.
 *
 * @author Benjamin Eberlei <kontakt@beberlei.de>
 */
abstract class ExpressionVisitor
{
    /**
     * Converts a comparison expression into the target query language output.
     *
     * @param Comparison $comparison
     *
     * @return mixed
     */
    abstract public function walkComparison(Comparison $comparison);

    /**
     * Converts a value expression into the target query language part.
     *
     * @param Value $value
     *
     * @return mixed
     */
    abstract public function walkValue(Value $value);

    /**
     * Converts a composite expression into the target query language output.
     *
     * @param CompositeExpression $expr
     *
     * @return mixed
     */
    abstract public function walkCompositeExpression(CompositeExpression $expr);

    /**
     * Dispatches walking an expression to the appropriate handler.
     *
     * @param Expression $expr
     *
     * @return mixed
     *
     * @throws \RuntimeException
     */
    public function dispatch(Expression $expr)
    {
        switch (true) {
            case ($expr instanceof Comparison):
                return $this->walkComparison($expr);

            case ($expr instanceof Value):
                return $this->walkValue($expr);

            case ($expr instanceof CompositeExpression):
                return $this->walkCompositeExpression($expr);

            default:
                throw new \RuntimeException("Unknown Expression " . get_class($expr));
        }
    }
}