# engine/reflection.py
# Copyright (C) 2005-2018 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""Provides an abstraction for obtaining database schema information.

Usage Notes:

Here are some general conventions when accessing the low level inspector
methods such as get_table_names, get_columns, etc.

1. Inspector methods return lists of dicts in most cases for the following
   reasons:

   * They're both standard types that can be serialized.
   * Using a dict instead of a tuple allows easy expansion of attributes.
   * Using a list for the outer structure maintains order and is easy to work
     with (e.g. list comprehension [d['name'] for d in cols]).

2. Records that contain a name, such as the column name in a column record
   use the key 'name'. So for most return values, each record will have a
   'name' attribute..
"""

from .. import exc, sql
from ..sql import schema as sa_schema
from .. import util
from ..sql.type_api import TypeEngine
from ..util import deprecated
from ..util import topological
from .. import inspection
from .base import Connectable


@util.decorator
def cache(fn, self, con, *args, **kw):
    info_cache = kw.get('info_cache', None)
    if info_cache is None:
        return fn(self, con, *args, **kw)
    key = (
        fn.__name__,
        tuple(a for a in args if isinstance(a, util.string_types)),
        tuple((k, v) for k, v in kw.items() if
              isinstance(v,
                         util.string_types + util.int_types + (float, )
                         )
              )
    )
    ret = info_cache.get(key)
    if ret is None:
        ret = fn(self, con, *args, **kw)
        info_cache[key] = ret
    return ret


class Inspector(object):
    """Performs database schema inspection.

    The Inspector acts as a proxy to the reflection methods of the
    :class:`~sqlalchemy.engine.interfaces.Dialect`, providing a
    consistent interface as well as caching support for previously
    fetched metadata.

    A :class:`.Inspector` object is usually created via the
    :func:`.inspect` function::

        from sqlalchemy import inspect, create_engine
        engine = create_engine('...')
        insp = inspect(engine)

    The inspection method above is equivalent to using the
    :meth:`.Inspector.from_engine` method, i.e.::

        engine = create_engine('...')
        insp = Inspector.from_engine(engine)

    Where above, the :class:`~sqlalchemy.engine.interfaces.Dialect` may opt
    to return an :class:`.Inspector` subclass that provides additional
    methods specific to the dialect's target database.

    """

    def __init__(self, bind):
        """Initialize a new :class:`.Inspector`.

        :param bind: a :class:`~sqlalchemy.engine.Connectable`,
          which is typically an instance of
          :class:`~sqlalchemy.engine.Engine` or
          :class:`~sqlalchemy.engine.Connection`.

        For a dialect-specific instance of :class:`.Inspector`, see
        :meth:`.Inspector.from_engine`

        """
        # this might not be a connection, it could be an engine.
        self.bind = bind

        # set the engine
        if hasattr(bind, 'engine'):
            self.engine = bind.engine
        else:
            self.engine = bind

        if self.engine is bind:
            # if engine, ensure initialized
            bind.connect().close()

        self.dialect = self.engine.dialect
        self.info_cache = {}

    @classmethod
    def from_engine(cls, bind):
        """Construct a new dialect-specific Inspector object from the given
        engine or connection.

        :param bind: a :class:`~sqlalchemy.engine.Connectable`,
          which is typically an instance of
          :class:`~sqlalchemy.engine.Engine` or
          :class:`~sqlalchemy.engine.Connection`.

        This method differs from direct a direct constructor call of
        :class:`.Inspector` in that the
        :class:`~sqlalchemy.engine.interfaces.Dialect` is given a chance to
        provide a dialect-specific :class:`.Inspector` instance, which may
        provide additional methods.

        See the example at :class:`.Inspector`.

        """
        if hasattr(bind.dialect, 'inspector'):
            return bind.dialect.inspector(bind)
        return Inspector(bind)

    @inspection._inspects(Connectable)
    def _insp(bind):
        return Inspector.from_engine(bind)

    @property
    def default_schema_name(self):
        """Return the default schema name presented by the dialect
        for the current engine's database user.

        E.g. this is typically ``public`` for PostgreSQL and ``dbo``
        for SQL Server.

        """
        return self.dialect.default_schema_name

    def get_schema_names(self):
        """Return all schema names.
        """

        if hasattr(self.dialect, 'get_schema_names'):
            return self.dialect.get_schema_names(self.bind,
                                                 info_cache=self.info_cache)
        return []

    def get_table_names(self, schema=None, order_by=None):
        """Return all table names in referred to within a particular schema.

        The names are expected to be real tables only, not views.
        Views are instead returned using the :meth:`.Inspector.get_view_names`
        method.


        :param schema: Schema name. If ``schema`` is left at ``None``, the
         database's default schema is
         used, else the named schema is searched.  If the database does not
         support named schemas, behavior is undefined if ``schema`` is not
         passed as ``None``.  For special quoting, use :class:`.quoted_name`.

        :param order_by: Optional, may be the string "foreign_key" to sort
         the result on foreign key dependencies.  Does not automatically
         resolve cycles, and will raise :class:`.CircularDependencyError`
         if cycles exist.

         .. deprecated:: 1.0.0 - see
            :meth:`.Inspector.get_sorted_table_and_fkc_names` for a version
            of this which resolves foreign key cycles between tables
            automatically.

         .. versionchanged:: 0.8 the "foreign_key" sorting sorts tables
            in order of dependee to dependent; that is, in creation
            order, rather than in drop order.  This is to maintain
            consistency with similar features such as
            :attr:`.MetaData.sorted_tables` and :func:`.util.sort_tables`.

        .. seealso::

            :meth:`.Inspector.get_sorted_table_and_fkc_names`

            :attr:`.MetaData.sorted_tables`

        """

        if hasattr(self.dialect, 'get_table_names'):
            tnames = self.dialect.get_table_names(
                self.bind, schema, info_cache=self.info_cache)
        else:
            tnames = self.engine.table_names(schema)
        if order_by == 'foreign_key':
            tuples = []
            for tname in tnames:
                for fkey in self.get_foreign_keys(tname, schema):
                    if tname != fkey['referred_table']:
                        tuples.append((fkey['referred_table'], tname))
            tnames = list(topological.sort(tuples, tnames))
        return tnames

    def get_sorted_table_and_fkc_names(self, schema=None):
        """Return dependency-sorted table and foreign key constraint names in
        referred to within a particular schema.

        This will yield 2-tuples of
        ``(tablename, [(tname, fkname), (tname, fkname), ...])``
        consisting of table names in CREATE order grouped with the foreign key
        constraint names that are not detected as belonging to a cycle.
        The final element
        will be ``(None, [(tname, fkname), (tname, fkname), ..])``
        which will consist of remaining
        foreign key constraint names that would require a separate CREATE
        step after-the-fact, based on dependencies between tables.

        .. versionadded:: 1.0.-

        .. seealso::

            :meth:`.Inspector.get_table_names`

            :func:`.sort_tables_and_constraints` - similar method which works
             with an already-given :class:`.MetaData`.

        """
        if hasattr(self.dialect, 'get_table_names'):
            tnames = self.dialect.get_table_names(
                self.bind, schema, info_cache=self.info_cache)
        else:
            tnames = self.engine.table_names(schema)

        tuples = set()
        remaining_fkcs = set()

        fknames_for_table = {}
        for tname in tnames:
            fkeys = self.get_foreign_keys(tname, schema)
            fknames_for_table[tname] = set(
                [fk['name'] for fk in fkeys]
            )
            for fkey in fkeys:
                if tname != fkey['referred_table']:
                    tuples.add((fkey['referred_table'], tname))
        try:
            candidate_sort = list(topological.sort(tuples, tnames))
        except exc.CircularDependencyError as err:
            for edge in err.edges:
                tuples.remove(edge)
                remaining_fkcs.update(
                    (edge[1], fkc)
                    for fkc in fknames_for_table[edge[1]]
                )

            candidate_sort = list(topological.sort(tuples, tnames))
        return [
            (tname, fknames_for_table[tname].difference(remaining_fkcs))
            for tname in candidate_sort
        ] + [(None, list(remaining_fkcs))]

    def get_temp_table_names(self):
        """return a list of temporary table names for the current bind.

        This method is unsupported by most dialects; currently
        only SQLite implements it.

        .. versionadded:: 1.0.0

        """
        return self.dialect.get_temp_table_names(
            self.bind, info_cache=self.info_cache)

    def get_temp_view_names(self):
        """return a list of temporary view names for the current bind.

        This method is unsupported by most dialects; currently
        only SQLite implements it.

        .. versionadded:: 1.0.0

        """
        return self.dialect.get_temp_view_names(
            self.bind, info_cache=self.info_cache)

    def get_table_options(self, table_name, schema=None, **kw):
        """Return a dictionary of options specified when the table of the
        given name was created.

        This currently includes some options that apply to MySQL tables.

        :param table_name: string name of the table.  For special quoting,
         use :class:`.quoted_name`.

        :param schema: string schema name; if omitted, uses the default schema
         of the database connection.  For special quoting,
         use :class:`.quoted_name`.

        """
        if hasattr(self.dialect, 'get_table_options'):
            return self.dialect.get_table_options(
                self.bind, table_name, schema,
                info_cache=self.info_cache, **kw)
        return {}

    def get_view_names(self, schema=None):
        """Return all view names in `schema`.

        :param schema: Optional, retrieve names from a non-default schema.
         For special quoting, use :class:`.quoted_name`.

        """

        return self.dialect.get_view_names(self.bind, schema,
                                           info_cache=self.info_cache)

    def get_view_definition(self, view_name, schema=None):
        """Return definition for `view_name`.

        :param schema: Optional, retrieve names from a non-default schema.
         For special quoting, use :class:`.quoted_name`.

        """

        return self.dialect.get_view_definition(
            self.bind, view_name, schema, info_cache=self.info_cache)

    def get_columns(self, table_name, schema=None, **kw):
        """Return information about columns in `table_name`.

        Given a string `table_name` and an optional string `schema`, return
        column information as a list of dicts with these keys:

        * ``name`` - the column's name

        * ``type`` - the type of this column; an instance of
          :class:`~sqlalchemy.types.TypeEngine`

        * ``nullable`` - boolean flag if the column is NULL or NOT NULL

        * ``default`` - the column's server default value - this is returned
          as a string SQL expression.

        * ``attrs``  - dict containing optional column attributes

        :param table_name: string name of the table.  For special quoting,
         use :class:`.quoted_name`.

        :param schema: string schema name; if omitted, uses the default schema
         of the database connection.  For special quoting,
         use :class:`.quoted_name`.

        :return: list of dictionaries, each representing the definition of
         a database column.

        """

        col_defs = self.dialect.get_columns(self.bind, table_name, schema,
                                            info_cache=self.info_cache,
                                            **kw)
        for col_def in col_defs:
            # make this easy and only return instances for coltype
            coltype = col_def['type']
            if not isinstance(coltype, TypeEngine):
                col_def['type'] = coltype()
        return col_defs

    @deprecated('0.7', 'Call to deprecated method get_primary_keys.'
                '  Use get_pk_constraint instead.')
    def get_primary_keys(self, table_name, schema=None, **kw):
        """Return information about primary keys in `table_name`.

        Given a string `table_name`, and an optional string `schema`, return
        primary key information as a list of column names.
        """

        return self.dialect.get_pk_constraint(self.bind, table_name, schema,
                                              info_cache=self.info_cache,
                                              **kw)['constrained_columns']

    def get_pk_constraint(self, table_name, schema=None, **kw):
        """Return information about primary key constraint on `table_name`.

        Given a string `table_name`, and an optional string `schema`, return
        primary key information as a dictionary with these keys:

        constrained_columns
          a list of column names that make up the primary key

        name
          optional name of the primary key constraint.

        :param table_name: string name of the table.  For special quoting,
         use :class:`.quoted_name`.

        :param schema: string schema name; if omitted, uses the default schema
         of the database connection.  For special quoting,
         use :class:`.quoted_name`.

        """
        return self.dialect.get_pk_constraint(self.bind, table_name, schema,
                                              info_cache=self.info_cache,
                                              **kw)

    def get_foreign_keys(self, table_name, schema=None, **kw):
        """Return information about foreign_keys in `table_name`.

        Given a string `table_name`, and an optional string `schema`, return
        foreign key information as a list of dicts with these keys:

        constrained_columns
          a list of column names that make up the foreign key

        referred_schema
          the name of the referred schema

        referred_table
          the name of the referred table

        referred_columns
          a list of column names in the referred table that correspond to
          constrained_columns

        name
          optional name of the foreign key constraint.

        :param table_name: string name of the table.  For special quoting,
         use :class:`.quoted_name`.

        :param schema: string schema name; if omitted, uses the default schema
         of the database connection.  For special quoting,
         use :class:`.quoted_name`.

        """

        return self.dialect.get_foreign_keys(self.bind, table_name, schema,
                                             info_cache=self.info_cache,
                                             **kw)

    def get_indexes(self, table_name, schema=None, **kw):
        """Return information about indexes in `table_name`.

        Given a string `table_name` and an optional string `schema`, return
        index information as a list of dicts with these keys:

        name
          the index's name

        column_names
          list of column names in order

        unique
          boolean

        dialect_options
          dict of dialect-specific index options.  May not be present
          for all dialects.

          .. versionadded:: 1.0.0

        :param table_name: string name of the table.  For special quoting,
         use :class:`.quoted_name`.

        :param schema: string schema name; if omitted, uses the default schema
         of the database connection.  For special quoting,
         use :class:`.quoted_name`.

        """

        return self.dialect.get_indexes(self.bind, table_name,
                                        schema,
                                        info_cache=self.info_cache, **kw)

    def get_unique_constraints(self, table_name, schema=None, **kw):
        """Return information about unique constraints in `table_name`.

        Given a string `table_name` and an optional string `schema`, return
        unique constraint information as a list of dicts with these keys:

        name
          the unique constraint's name

        column_names
          list of column names in order

        :param table_name: string name of the table.  For special quoting,
         use :class:`.quoted_name`.

        :param schema: string schema name; if omitted, uses the default schema
         of the database connection.  For special quoting,
         use :class:`.quoted_name`.

        .. versionadded:: 0.8.4

        """

        return self.dialect.get_unique_constraints(
            self.bind, table_name, schema, info_cache=self.info_cache, **kw)

    def get_table_comment(self, table_name, schema=None, **kw):
        """Return information about the table comment for ``table_name``.

        Given a string ``table_name`` and an optional string ``schema``,
        return table comment information as a dictionary with these keys:

        text
            text of the comment.

        Raises ``NotImplementedError`` for a dialect that does not support
        comments.

        .. versionadded:: 1.2

        """

        return self.dialect.get_table_comment(
            self.bind, table_name, schema, info_cache=self.info_cache,
            **kw)

    def get_check_constraints(self, table_name, schema=None, **kw):
        """Return information about check constraints in `table_name`.

        Given a string `table_name` and an optional string `schema`, return
        check constraint information as a list of dicts with these keys:

        name
          the check constraint's name

        sqltext
          the check constraint's SQL expression

        :param table_name: string name of the table.  For special quoting,
         use :class:`.quoted_name`.

        :param schema: string schema name; if omitted, uses the default schema
         of the database connection.  For special quoting,
         use :class:`.quoted_name`.

        .. versionadded:: 1.1.0

        """

        return self.dialect.get_check_constraints(
            self.bind, table_name, schema, info_cache=self.info_cache, **kw)

    def reflecttable(self, table, include_columns, exclude_columns=(),
                     _extend_on=None):
        """Given a Table object, load its internal constructs based on
        introspection.

        This is the underlying method used by most dialects to produce
        table reflection.  Direct usage is like::

            from sqlalchemy import create_engine, MetaData, Table
            from sqlalchemy.engine.reflection import Inspector

            engine = create_engine('...')
            meta = MetaData()
            user_table = Table('user', meta)
            insp = Inspector.from_engine(engine)
            insp.reflecttable(user_table, None)

        :param table: a :class:`~sqlalchemy.schema.Table` instance.
        :param include_columns: a list of string column names to include
          in the reflection process.  If ``None``, all columns are reflected.

        """

        if _extend_on is not None:
            if table in _extend_on:
                return
            else:
                _extend_on.add(table)

        dialect = self.bind.dialect

        schema = self.bind.schema_for_object(table)

        table_name = table.name

        # get table-level arguments that are specifically
        # intended for reflection, e.g. oracle_resolve_synonyms.
        # these are unconditionally passed to related Table
        # objects
        reflection_options = dict(
            (k, table.dialect_kwargs.get(k))
            for k in dialect.reflection_options
            if k in table.dialect_kwargs
        )

        # reflect table options, like mysql_engine
        tbl_opts = self.get_table_options(
            table_name, schema, **table.dialect_kwargs)
        if tbl_opts:
            # add additional kwargs to the Table if the dialect
            # returned them
            table._validate_dialect_kwargs(tbl_opts)

        if util.py2k:
            if isinstance(schema, str):
                schema = schema.decode(dialect.encoding)
            if isinstance(table_name, str):
                table_name = table_name.decode(dialect.encoding)

        found_table = False
        cols_by_orig_name = {}

        for col_d in self.get_columns(
                table_name, schema, **table.dialect_kwargs):
            found_table = True

            self._reflect_column(
                table, col_d, include_columns,
                exclude_columns, cols_by_orig_name)

        if not found_table:
            raise exc.NoSuchTableError(table.name)

        self._reflect_pk(
            table_name, schema, table, cols_by_orig_name, exclude_columns)

        self._reflect_fk(
            table_name, schema, table, cols_by_orig_name,
            exclude_columns, _extend_on, reflection_options)

        self._reflect_indexes(
            table_name, schema, table, cols_by_orig_name,
            include_columns, exclude_columns, reflection_options)

        self._reflect_unique_constraints(
            table_name, schema, table, cols_by_orig_name,
            include_columns, exclude_columns, reflection_options)

        self._reflect_check_constraints(
            table_name, schema, table, cols_by_orig_name,
            include_columns, exclude_columns, reflection_options)

        self._reflect_table_comment(
            table_name, schema, table, reflection_options
        )

    def _reflect_column(
        self, table, col_d, include_columns,
            exclude_columns, cols_by_orig_name):

        orig_name = col_d['name']

        table.dispatch.column_reflect(self, table, col_d)

        # fetch name again as column_reflect is allowed to
        # change it
        name = col_d['name']
        if (include_columns and name not in include_columns) \
                or (exclude_columns and name in exclude_columns):
            return

        coltype = col_d['type']

        col_kw = dict(
            (k, col_d[k])
            for k in ['nullable', 'autoincrement', 'quote', 'info', 'key', 'comment']
            if k in col_d
        )

        colargs = []
        if col_d.get('default') is not None:
            default = col_d['default']
            if isinstance(default, sql.elements.TextClause):
                default = sa_schema.DefaultClause(default, _reflected=True)
            elif not isinstance(default, sa_schema.FetchedValue):
                default = sa_schema.DefaultClause(
                    sql.text(col_d['default']), _reflected=True)

            colargs.append(default)

        if 'sequence' in col_d:
            self._reflect_col_sequence(col_d, colargs)

        cols_by_orig_name[orig_name] = col = \
            sa_schema.Column(name, coltype, *colargs, **col_kw)

        if col.key in table.primary_key:
            col.primary_key = True
        table.append_column(col)

    def _reflect_col_sequence(self, col_d, colargs):
        if 'sequence' in col_d:
            # TODO: mssql and sybase are using this.
            seq = col_d['sequence']
            sequence = sa_schema.Sequence(seq['name'], 1, 1)
            if 'start' in seq:
                sequence.start = seq['start']
            if 'increment' in seq:
                sequence.increment = seq['increment']
            colargs.append(sequence)

    def _reflect_pk(
            self, table_name, schema, table,
            cols_by_orig_name, exclude_columns):
        pk_cons = self.get_pk_constraint(
            table_name, schema, **table.dialect_kwargs)
        if pk_cons:
            pk_cols = [
                cols_by_orig_name[pk]
                for pk in pk_cons['constrained_columns']
                if pk in cols_by_orig_name and pk not in exclude_columns
            ]

            # update pk constraint name
            table.primary_key.name = pk_cons.get('name')

            # tell the PKConstraint to re-initialize
            # its column collection
            table.primary_key._reload(pk_cols)

    def _reflect_fk(
            self, table_name, schema, table, cols_by_orig_name,
            exclude_columns, _extend_on, reflection_options):
        fkeys = self.get_foreign_keys(
            table_name, schema, **table.dialect_kwargs)
        for fkey_d in fkeys:
            conname = fkey_d['name']
            # look for columns by orig name in cols_by_orig_name,
            # but support columns that are in-Python only as fallback
            constrained_columns = [
                cols_by_orig_name[c].key
                if c in cols_by_orig_name else c
                for c in fkey_d['constrained_columns']
            ]
            if exclude_columns and set(constrained_columns).intersection(
                    exclude_columns):
                continue
            referred_schema = fkey_d['referred_schema']
            referred_table = fkey_d['referred_table']
            referred_columns = fkey_d['referred_columns']
            refspec = []
            if referred_schema is not None:
                sa_schema.Table(referred_table, table.metadata,
                                autoload=True, schema=referred_schema,
                                autoload_with=self.bind,
                                _extend_on=_extend_on,
                                **reflection_options
                                )
                for column in referred_columns:
                    refspec.append(".".join(
                        [referred_schema, referred_table, column]))
            else:
                sa_schema.Table(referred_table, table.metadata, autoload=True,
                                autoload_with=self.bind,
                                schema=sa_schema.BLANK_SCHEMA,
                                _extend_on=_extend_on,
                                **reflection_options
                                )
                for column in referred_columns:
                    refspec.append(".".join([referred_table, column]))
            if 'options' in fkey_d:
                options = fkey_d['options']
            else:
                options = {}
            table.append_constraint(
                sa_schema.ForeignKeyConstraint(constrained_columns, refspec,
                                               conname, link_to_name=True,
                                               **options))

    def _reflect_indexes(
        self, table_name, schema, table, cols_by_orig_name,
            include_columns, exclude_columns, reflection_options):
        # Indexes
        indexes = self.get_indexes(table_name, schema)
        for index_d in indexes:
            name = index_d['name']
            columns = index_d['column_names']
            unique = index_d['unique']
            flavor = index_d.get('type', 'index')
            dialect_options = index_d.get('dialect_options', {})

            duplicates = index_d.get('duplicates_constraint')
            if include_columns and \
                    not set(columns).issubset(include_columns):
                util.warn(
                    "Omitting %s key for (%s), key covers omitted columns." %
                    (flavor, ', '.join(columns)))
                continue
            if duplicates:
                continue
            # look for columns by orig name in cols_by_orig_name,
            # but support columns that are in-Python only as fallback
            idx_cols = []
            for c in columns:
                try:
                    idx_col = cols_by_orig_name[c] \
                        if c in cols_by_orig_name else table.c[c]
                except KeyError:
                    util.warn(
                        "%s key '%s' was not located in "
                        "columns for table '%s'" % (
                            flavor, c, table_name
                        ))
                else:
                    idx_cols.append(idx_col)

            sa_schema.Index(
                name, *idx_cols,
                _table=table,
                **dict(list(dialect_options.items()) + [('unique', unique)])
            )

    def _reflect_unique_constraints(
        self, table_name, schema, table, cols_by_orig_name,
            include_columns, exclude_columns, reflection_options):

        # Unique Constraints
        try:
            constraints = self.get_unique_constraints(table_name, schema)
        except NotImplementedError:
            # optional dialect feature
            return

        for const_d in constraints:
            conname = const_d['name']
            columns = const_d['column_names']
            duplicates = const_d.get('duplicates_index')
            if include_columns and \
                    not set(columns).issubset(include_columns):
                util.warn(
                    "Omitting unique constraint key for (%s), "
                    "key covers omitted columns." %
                    ', '.join(columns))
                continue
            if duplicates:
                continue
            # look for columns by orig name in cols_by_orig_name,
            # but support columns that are in-Python only as fallback
            constrained_cols = []
            for c in columns:
                try:
                    constrained_col = cols_by_orig_name[c] \
                        if c in cols_by_orig_name else table.c[c]
                except KeyError:
                    util.warn(
                        "unique constraint key '%s' was not located in "
                        "columns for table '%s'" % (c, table_name))
                else:
                    constrained_cols.append(constrained_col)
            table.append_constraint(
                sa_schema.UniqueConstraint(*constrained_cols, name=conname))

    def _reflect_check_constraints(
            self, table_name, schema, table, cols_by_orig_name,
            include_columns, exclude_columns, reflection_options):
        try:
            constraints = self.get_check_constraints(table_name, schema)
        except NotImplementedError:
            # optional dialect feature
            return

        for const_d in constraints:
            table.append_constraint(
                sa_schema.CheckConstraint(**const_d))

    def _reflect_table_comment(
            self, table_name, schema, table, reflection_options):
        try:
            comment_dict = self.get_table_comment(table_name, schema)
        except NotImplementedError:
            return
        else:
            table.comment = comment_dict.get('text', None)
