framework/db/QueryBuilder.php
public function getExpressionBuilder(ExpressionInterface $expression)
    {
        $className = get_class($expression);

        if (!isset($this->expressionBuilders[$className])) {
            foreach (array_reverse($this->expressionBuilders) as $expressionClass => $builderClass) {
                if (is_subclass_of($expression, $expressionClass)) {
                    $this->expressionBuilders[$className] = $builderClass;
                    break;
                }
            }

            if (!isset($this->expressionBuilders[$className])) {
                throw new InvalidArgumentException('Expression of class ' . $className . ' can not be built in ' . get_class($this));
            }
        }

        if ($this->expressionBuilders[$className] === __CLASS__) {
            return $this;
        }

        if (!is_object($this->expressionBuilders[$className])) {
            $this->expressionBuilders[$className] = new $this->expressionBuilders[$className]($this);
        }

        return $this->expressionBuilders[$className];
    }
public function getExpressionBuilder(ExpressionInterface $expression)
    {
        $className = get_class($expression);

        if (!isset($this->expressionBuilders[$className])) {
            foreach (array_reverse($this->expressionBuilders) as $expressionClass => $builderClass) {
                if (is_subclass_of($expression, $expressionClass)) {
                    $this->expressionBuilders[$className] = $builderClass;
                    break;
                }
            }

            if (!isset($this->expressionBuilders[$className])) {
                throw new InvalidArgumentException('Expression of class ' . $className . ' can not be built in ' . get_class($this));
            }
        }

        if ($this->expressionBuilders[$className] === __CLASS__) {
            return $this;
        }

        if (!is_object($this->expressionBuilders[$className])) {
            $this->expressionBuilders[$className] = new $this->expressionBuilders[$className]($this);
        }

        return $this->expressionBuilders[$className];
    }
Gets object of [[ExpressionBuilderInterface]] that is suitable for $expression.
Uses [[expressionBuilders]] array to find a suitable builder class.

@param ExpressionInterface $expression
@return ExpressionBuilderInterface
@see expressionBuilders
@since 2.0.14
@throws InvalidArgumentException when $expression building is not supported by this QueryBuilder.