Doctrine\ORM\Tools\SchemaTool::_gatherRelationsSql PHP Method

    private function _gatherRelationsSql($class, $table, $schema)
    {
        foreach ($class->associationMappings as $fieldName => $mapping) {
            if (isset($mapping['inherited'])) {
                continue;
            }

            $foreignClass = $this->_em->getClassMetadata($mapping['targetEntity']);

            if ($mapping['type'] & ClassMetadata::TO_ONE && $mapping['isOwningSide']) {
                $primaryKeyColumns = $uniqueConstraints = array(); // PK is unnecessary for this relation-type

                $this->_gatherRelationJoinColumns($mapping['joinColumns'], $table, $foreignClass, $mapping, $primaryKeyColumns, $uniqueConstraints);

                foreach($uniqueConstraints AS $indexName => $unique) {
                    $table->addUniqueIndex($unique['columns'], is_numeric($indexName) ? null : $indexName);
                }
            } else if ($mapping['type'] == ClassMetadata::ONE_TO_MANY && $mapping['isOwningSide']) {
                //... create join table, one-many through join table supported later
                throw ORMException::notSupported();
            } else if ($mapping['type'] == ClassMetadata::MANY_TO_MANY && $mapping['isOwningSide']) {
                // create join table
                $joinTable = $mapping['joinTable'];

                $theJoinTable = $schema->createTable($foreignClass->getQuotedJoinTableName($mapping, $this->_platform));

                $primaryKeyColumns = $uniqueConstraints = array();

                // Build first FK constraint (relation table => source table)
                $this->_gatherRelationJoinColumns($joinTable['joinColumns'], $theJoinTable, $class, $mapping, $primaryKeyColumns, $uniqueConstraints);

                // Build second FK constraint (relation table => target table)
                $this->_gatherRelationJoinColumns($joinTable['inverseJoinColumns'], $theJoinTable, $foreignClass, $mapping, $primaryKeyColumns, $uniqueConstraints);

                $theJoinTable->setPrimaryKey($primaryKeyColumns);

                foreach($uniqueConstraints AS $indexName => $unique) {
                    $theJoinTable->addUniqueIndex($unique['columns'], is_numeric($indexName) ? null : $indexName);
                }
            }
        }
    }