code: def publish(self):
      df = self._data
      feature_metadata = lore.metadata.FeatureMetaData.create(
          created_at=datetime.utcnow(),
          entity_name=self.entity_name,
          feature_name=self.name,
          version=self.version,
          snapshot_at=self.timestamp,
          feature_dtypes=self.dtypes,
          s3_url=None,
      )
      df["feature_metadata_id"] = feature_metadata.id
      lore.io.metadata.insert("features", df)
  
file_path: lore/lore/features/db.py
imports: from abc import ABCMeta
  from datetime import datetime
  import lore.io
  from lore.features.base import BaseFeatureExporter, BaseFeatureImporter
  import lore.metadata
  from lore.metadata import FeatureMetaData
  from sqlalchemy.orm import sessionmaker, scoped_session
  import pandas
  from lore.util import convert_df_columns_to_json
  import json
label_desc: Use image node_id 4 for calling the DBFeatureExporter obj's underlying member method code with example usage: obj.publish() without return types