# Django 2.2.9.dev20191202104323 文档

# django.contrib.postgres.indexes 源代码

    from django.db.models import Index
    from django.db.utils import NotSupportedError
    from django.utils.functional import cached_property

    __all__ = [
        'BrinIndex', 'BTreeIndex', 'GinIndex', 'GistIndex', 'HashIndex',
        'SpGistIndex',
    ]

    class PostgresIndex(Index):

        @cached_property
        def max_name_length(self):
            # Allow an index name longer than 30 characters when the suffix is
            # longer than the usual 3 character limit. The 30 character limit for
            # cross-database compatibility isn't applicable to PostgreSQL-specific
            # indexes.
            return Index.max_name_length - len(Index.suffix) + len(self.suffix)

        def create_sql(self, model, schema_editor, using=''):
            self.check_supported(schema_editor)
            statement = super().create_sql(model, schema_editor, using=' USING %s' % self.suffix)
            with_params = self.get_with_params()
            if with_params:
                statement.parts['extra'] = 'WITH (%s) %s' % (
                    ', '.join(with_params),
                    statement.parts['extra'],
                )
            return statement

        def check_supported(self, schema_editor):
            pass

        def get_with_params(self):
            return []

    class BrinIndex(PostgresIndex):
        suffix = 'brin'

        def __init__(self, *, autosummarize=None, pages_per_range=None, **kwargs):
            if pages_per_range is not None and pages_per_range <= 0:
                raise ValueError('pages_per_range must be None or a positive integer')
            self.autosummarize = autosummarize
            self.pages_per_range = pages_per_range
            super().__init__(**kwargs)

        def deconstruct(self):
            path, args, kwargs = super().deconstruct()
            if self.autosummarize is not None:
                kwargs['autosummarize'] = self.autosummarize
            if self.pages_per_range is not None:
                kwargs['pages_per_range'] = self.pages_per_range
            return path, args, kwargs

        def check_supported(self, schema_editor):
            if not schema_editor.connection.features.has_brin_index_support:
                raise NotSupportedError('BRIN indexes require PostgreSQL 9.5+.')
            if self.autosummarize and not schema_editor.connection.features.has_brin_autosummarize:
                raise NotSupportedError('BRIN option autosummarize requires PostgreSQL 10+.')

        def get_with_params(self):
            with_params = []
            if self.autosummarize is not None:
                with_params.append('autosummarize = %s' % ('on' if self.autosummarize else 'off'))
            if self.pages_per_range is not None:
                with_params.append('pages_per_range = %d' % self.pages_per_range)
            return with_params

    class BTreeIndex(PostgresIndex):
        suffix = 'btree'

        def __init__(self, *, fillfactor=None, **kwargs):
            self.fillfactor = fillfactor
            super().__init__(**kwargs)

        def deconstruct(self):
            path, args, kwargs = super().deconstruct()
            if self.fillfactor is not None:
                kwargs['fillfactor'] = self.fillfactor
            return path, args, kwargs

        def get_with_params(self):
            with_params = []
            if self.fillfactor is not None:
                with_params.append('fillfactor = %d' % self.fillfactor)
            return with_params

    class GinIndex(PostgresIndex):
        suffix = 'gin'

        def __init__(self, *, fastupdate=None, gin_pending_list_limit=None, **kwargs):
            self.fastupdate = fastupdate
            self.gin_pending_list_limit = gin_pending_list_limit
            super().__init__(**kwargs)

        def deconstruct(self):
            path, args, kwargs = super().deconstruct()
            if self.fastupdate is not None:
                kwargs['fastupdate'] = self.fastupdate
            if self.gin_pending_list_limit is not None:
                kwargs['gin_pending_list_limit'] = self.gin_pending_list_limit
            return path, args, kwargs

        def check_supported(self, schema_editor):
            if self.gin_pending_list_limit and not schema_editor.connection.features.has_gin_pending_list_limit:
                raise NotSupportedError('GIN option gin_pending_list_limit requires PostgreSQL 9.5+.')

        def get_with_params(self):
            with_params = []
            if self.gin_pending_list_limit is not None:
                with_params.append('gin_pending_list_limit = %d' % self.gin_pending_list_limit)
            if self.fastupdate is not None:
                with_params.append('fastupdate = %s' % ('on' if self.fastupdate else 'off'))
            return with_params

    class GistIndex(PostgresIndex):
        suffix = 'gist'

        def __init__(self, *, buffering=None, fillfactor=None, **kwargs):
            self.buffering = buffering
            self.fillfactor = fillfactor
            super().__init__(**kwargs)

        def deconstruct(self):
            path, args, kwargs = super().deconstruct()
            if self.buffering is not None:
                kwargs['buffering'] = self.buffering
            if self.fillfactor is not None:
                kwargs['fillfactor'] = self.fillfactor
            return path, args, kwargs

        def get_with_params(self):
            with_params = []
            if self.buffering is not None:
                with_params.append('buffering = %s' % ('on' if self.buffering else 'off'))
            if self.fillfactor is not None:
                with_params.append('fillfactor = %d' % self.fillfactor)
            return with_params

    class HashIndex(PostgresIndex):
        suffix = 'hash'

        def __init__(self, *, fillfactor=None, **kwargs):
            self.fillfactor = fillfactor
            super().__init__(**kwargs)

        def deconstruct(self):
            path, args, kwargs = super().deconstruct()
            if self.fillfactor is not None:
                kwargs['fillfactor'] = self.fillfactor
            return path, args, kwargs

        def get_with_params(self):
            with_params = []
            if self.fillfactor is not None:
                with_params.append('fillfactor = %d' % self.fillfactor)
            return with_params

    class SpGistIndex(PostgresIndex):
        suffix = 'spgist'

        def __init__(self, *, fillfactor=None, **kwargs):
            self.fillfactor = fillfactor
            super().__init__(**kwargs)

        def deconstruct(self):
            path, args, kwargs = super().deconstruct()
            if self.fillfactor is not None:
                kwargs['fillfactor'] = self.fillfactor
            return path, args, kwargs

        def get_with_params(self):
            with_params = []
            if self.fillfactor is not None:
                with_params.append('fillfactor = %d' % self.fillfactor)
            return with_params