Amundsen Postgres version of a metadata extractor. Only tested on 9.6, on local install. No tests provided at this point

postgres_table_metadata_extractor.py

import logging
from collections import namedtuple

from pyhocon import ConfigFactory, ConfigTree  # noqa: F401
from typing import Iterator, Union, Dict, Any  # noqa: F401

from databuilder import Scoped
from databuilder.extractor.base_extractor import Extractor
from databuilder.extractor.sql_alchemy_extractor import SQLAlchemyExtractor
from databuilder.models.table_metadata import TableMetadata, ColumnMetadata
from itertools import groupby


TableKey = namedtuple('TableKey', ['schema_name', 'table_name'])

LOGGER = logging.getLogger(__name__)


class PostgresTableMetadataExtractor(Extractor):
    """
    Extracts Postgres table and column metadata from underlying meta store database using SQLAlchemyExtractor
    """
    # SELECT statement from postgres information_schema to extract table and column metadata
    SQL_STATEMENT = """
    SELECT 
      c.table_catalog as cluster, c.table_schema as schema_name, c.table_name as name, null as description, c.column_name as col_name, c.data_type as col_type, null as col_description, ordinal_position as col_sort_order

    FROM INFORMATION_SCHEMA.COLUMNS c
    {where_clause_suffix}
    ORDER by cluster, schema_name, name, col_sort_order ;
    """

    # CONFIG KEYS
    WHERE_CLAUSE_SUFFIX_KEY = 'where_clause_suffix'
    CLUSTER_KEY = 'master'

    DEFAULT_CONFIG = ConfigFactory.from_dict({WHERE_CLAUSE_SUFFIX_KEY: ' ', CLUSTER_KEY: 'master'})

    def init(self, conf):
        # type: (ConfigTree) -> None
        conf = conf.with_fallback(PostgresTableMetadataExtractor.DEFAULT_CONFIG)
        self._cluster = '{}'.format(conf.get_string(PostgresTableMetadataExtractor.CLUSTER_KEY))

        self.sql_stmt = PostgresTableMetadataExtractor.SQL_STATEMENT.format(
            where_clause_suffix=conf.get_string(PostgresTableMetadataExtractor.WHERE_CLAUSE_SUFFIX_KEY))

        LOGGER.info('SQL for postgres metadata: {}'.format(self.sql_stmt))

        self._alchemy_extractor = SQLAlchemyExtractor()
        sql_alch_conf = Scoped.get_scoped_conf(conf, self._alchemy_extractor.get_scope())\
            .with_fallback(ConfigFactory.from_dict({SQLAlchemyExtractor.EXTRACT_SQL: self.sql_stmt}))

        self._alchemy_extractor.init(sql_alch_conf)
        self._extract_iter = None  # type: Union[None, Iterator]

    def extract(self):
        # type: () -> Union[TableMetadata, None]
        if not self._extract_iter:
            self._extract_iter = self._get_extract_iter()
        try:
            return next(self._extract_iter)
        except StopIteration:
            return None

    def get_scope(self):
        # type: () -> str
        return 'extractor.postgres_table_metadata'

    def _get_extract_iter(self):
        # type: () -> Iterator[TableMetadata]
        """
        Using itertools.groupby and raw level iterator, it groups to table and yields TableMetadata
        :return:
        """
        for key, group in groupby(self._get_raw_extract_iter(), self._get_table_key):
            columns = []

            for row in group:
                last_row = row
                columns.append(ColumnMetadata(row['col_name'], row['col_description'],
                                              row['col_type'], row['col_sort_order']))

            yield TableMetadata('postgres', last_row['cluster'],
                                last_row['schema_name'],
                                last_row['name'],
                                last_row['description'],
                                columns)

    def _get_raw_extract_iter(self):
        # type: () -> Iterator[Dict[str, Any]]
        """
        Provides iterator of result row from SQLAlchemy extractor
        :return:
        """
        row = self._alchemy_extractor.extract()
        while row:
            yield row
            row = self._alchemy_extractor.extract()

    def _get_table_key(self, row):
        # type: (Dict[str, Any]) -> Union[TableKey, None]
        """
        Table key consists of schema and table name
        :param row:
        :return:
        """
        if row:
            return TableKey(schema_name=row['schema_name'], table_name=row['name'])

        return None

hey @p5k6, saw you created this gist for postgres extractor. I think it would be a goo addition to Amundsen databuilder. Do you think you have time to create an Amundsen databuilder pr with unit test for this extractor?