SqlContentEntityStorageSchema::getSharedTableFieldSchema

protected SqlContentEntityStorageSchema::getSharedTableFieldSchema(FieldStorageDefinitionInterface $storage_definition, $table_name, array $column_mapping)

protected function getSharedTableFieldSchema(FieldStorageDefinitionInterface $storage_definition, $table_name, array $column_mapping) {
  $schema = array();
  $field_schema = $storage_definition->getSchema();

  // Check that the schema does not include forbidden column names.
  if (array_intersect(array_keys($field_schema['columns']), $this->storage->getTableMapping()->getReservedColumns())) {
    throw new FieldException("Illegal field column names on {$storage_definition->getName()}");
  }

  $field_name = $storage_definition->getName();
  $base_table = $this->storage->getBaseTable();

  // A shared table contains rows for entities where the field is empty
  // (since other fields stored in the same table might not be empty), thus
  // the only columns that can be 'not null' are those for required
  // properties of required fields. However, even those would break in the
  // case where a new field is added to a table that contains existing rows.
  // For now, we only hardcode 'not null' to a couple "entity keys", in order
  // to keep their indexes optimized.
  // @todo Revisit once we have support for 'initial' in
  //   https://www.drupal.org/node/2346019.
  $not_null_keys = $this->entityType->getKeys();
  // Label fields are not necessarily required.
  unset($not_null_keys['label']);
  // Because entity ID and revision ID are both serial fields in the base and
  // revision table respectively, the revision ID is not known yet, when
  // inserting data into the base table. Instead the revision ID in the base
  // table is updated after the data has been inserted into the revision
  // table. For this reason the revision ID field cannot be marked as NOT
  // NULL.
  if ($table_name == $base_table) {
    unset($not_null_keys['revision']);
  }

  foreach ($column_mapping as $field_column_name => $schema_field_name) {
    $column_schema = $field_schema['columns'][$field_column_name];

    $schema['fields'][$schema_field_name] = $column_schema;
    $schema['fields'][$schema_field_name]['not null'] = in_array($field_name, $not_null_keys);
  }

  if (!empty($field_schema['indexes'])) {
    $schema['indexes'] = $this->getFieldIndexes($field_name, $field_schema, $column_mapping);
  }

  if (!empty($field_schema['unique keys'])) {
    $schema['unique keys'] = $this->getFieldUniqueKeys($field_name, $field_schema, $column_mapping);
  }

  if (!empty($field_schema['foreign keys'])) {
    $schema['foreign keys'] = $this->getFieldForeignKeys($field_name, $field_schema, $column_mapping);
  }

  return $schema;
}