superset/db_engine_specs/postgres.py

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import re
from datetime import datetime
from typing import Any, Dict, List, Optional, Tuple, TYPE_CHECKING

from pytz import _FixedOffset  # type: ignore
from sqlalchemy.dialects.postgresql.base import PGInspector

from superset.db_engine_specs.base import BaseEngineSpec
from superset.utils import core as utils

if TYPE_CHECKING:
    from superset.models.core import Database  # pragma: no cover


# Replace psycopg2.tz.FixedOffsetTimezone with pytz, which is serializable by PyArrow
# https://github.com/stub42/pytz/blob/b70911542755aeeea7b5a9e066df5e1c87e8f2c8/src/pytz/reference.py#L25
class FixedOffsetTimezone(_FixedOffset):
    pass


class PostgresBaseEngineSpec(BaseEngineSpec):
    """ Abstract class for Postgres 'like' databases """

    engine = ""
    engine_name = "PostgreSQL"

    _time_grain_expressions = {
        None: "{col}",
        "PT1S": "DATE_TRUNC('second', {col})",
        "PT1M": "DATE_TRUNC('minute', {col})",
        "PT1H": "DATE_TRUNC('hour', {col})",
        "P1D": "DATE_TRUNC('day', {col})",
        "P1W": "DATE_TRUNC('week', {col})",
        "P1M": "DATE_TRUNC('month', {col})",
        "P0.25Y": "DATE_TRUNC('quarter', {col})",
        "P1Y": "DATE_TRUNC('year', {col})",
    }

    @classmethod
    def fetch_data(
        cls, cursor: Any, limit: Optional[int] = None
    ) -> List[Tuple[Any, ...]]:
        cursor.tzinfo_factory = FixedOffsetTimezone
        if not cursor.description:
            return []
        return super().fetch_data(cursor, limit)

    @classmethod
    def epoch_to_dttm(cls) -> str:
        return "(timestamp 'epoch' + {col} * interval '1 second')"


class PostgresEngineSpec(PostgresBaseEngineSpec):
    engine = "postgresql"
    engine_aliases = ("postgres",)
    max_column_name_length = 63
    try_remove_schema_from_table_name = False

    @classmethod
    def get_allow_cost_estimate(cls, extra: Dict[str, Any]) -> bool:
        return True

    @classmethod
    def estimate_statement_cost(cls, statement: str, cursor: Any) -> Dict[str, Any]:
        sql = f"EXPLAIN {statement}"
        cursor.execute(sql)

        result = cursor.fetchone()[0]
        match = re.search(r"cost=([\d\.]+)\.\.([\d\.]+)", result)
        if match:
            return {
                "Start-up cost": float(match.group(1)),
                "Total cost": float(match.group(2)),
            }

        return {}

    @classmethod
    def query_cost_formatter(
        cls, raw_cost: List[Dict[str, Any]]
    ) -> List[Dict[str, str]]:
        return [{k: str(v) for k, v in row.items()} for row in raw_cost]

    @classmethod
    def get_table_names(
        cls, database: "Database", inspector: PGInspector, schema: Optional[str]
    ) -> List[str]:
        """Need to consider foreign tables for PostgreSQL"""
        tables = inspector.get_table_names(schema)
        tables.extend(inspector.get_foreign_table_names(schema))
        return sorted(tables)

    @classmethod
    def convert_dttm(cls, target_type: str, dttm: datetime) -> Optional[str]:
        tt = target_type.upper()
        if tt == utils.TemporalType.DATE:
            return f"TO_DATE('{dttm.date().isoformat()}', 'YYYY-MM-DD')"
        if tt == utils.TemporalType.TIMESTAMP:
            dttm_formatted = dttm.isoformat(sep=" ", timespec="microseconds")
            return f"""TO_TIMESTAMP('{dttm_formatted}', 'YYYY-MM-DD HH24:MI:SS.US')"""
        return None