my-first-blog/myvenv/Lib/site-packages/django/db/backends/postgresql/introspection.py

from django.db.backends.base.introspection import (
    BaseDatabaseIntrospection, FieldInfo, TableInfo,
)
from django.db.models.indexes import Index


class DatabaseIntrospection(BaseDatabaseIntrospection):
    # Maps type codes to Django Field types.
    data_types_reverse = {
        16: 'BooleanField',
        17: 'BinaryField',
        20: 'BigIntegerField',
        21: 'SmallIntegerField',
        23: 'IntegerField',
        25: 'TextField',
        700: 'FloatField',
        701: 'FloatField',
        869: 'GenericIPAddressField',
        1042: 'CharField',  # blank-padded
        1043: 'CharField',
        1082: 'DateField',
        1083: 'TimeField',
        1114: 'DateTimeField',
        1184: 'DateTimeField',
        1186: 'DurationField',
        1266: 'TimeField',
        1700: 'DecimalField',
        2950: 'UUIDField',
    }

    ignored_tables = []

    def get_field_type(self, data_type, description):
        field_type = super().get_field_type(data_type, description)
        if description.default and 'nextval' in description.default:
            if field_type == 'IntegerField':
                return 'AutoField'
            elif field_type == 'BigIntegerField':
                return 'BigAutoField'
        return field_type

    def get_table_list(self, cursor):
        """Return a list of table and view names in the current database."""
        cursor.execute("""
            SELECT c.relname,
            CASE WHEN {} THEN 'p' WHEN c.relkind IN ('m', 'v') THEN 'v' ELSE 't' END
            FROM pg_catalog.pg_class c
            LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
            WHERE c.relkind IN ('f', 'm', 'p', 'r', 'v')
                AND n.nspname NOT IN ('pg_catalog', 'pg_toast')
                AND pg_catalog.pg_table_is_visible(c.oid)
        """.format('c.relispartition' if self.connection.features.supports_table_partitions else 'FALSE'))
        return [TableInfo(*row) for row in cursor.fetchall() if row[0] not in self.ignored_tables]

    def get_table_description(self, cursor, table_name):
        """
        Return a description of the table with the DB-API cursor.description
        interface.
        """
        # Query the pg_catalog tables as cursor.description does not reliably
        # return the nullable property and information_schema.columns does not
        # contain details of materialized views.
        cursor.execute("""
            SELECT
                a.attname AS column_name,
                NOT (a.attnotnull OR (t.typtype = 'd' AND t.typnotnull)) AS is_nullable,
                pg_get_expr(ad.adbin, ad.adrelid) AS column_default
            FROM pg_attribute a
            LEFT JOIN pg_attrdef ad ON a.attrelid = ad.adrelid AND a.attnum = ad.adnum
            JOIN pg_type t ON a.atttypid = t.oid
            JOIN pg_class c ON a.attrelid = c.oid
            JOIN pg_namespace n ON c.relnamespace = n.oid
            WHERE c.relkind IN ('f', 'm', 'p', 'r', 'v')
                AND c.relname = %s
                AND n.nspname NOT IN ('pg_catalog', 'pg_toast')
                AND pg_catalog.pg_table_is_visible(c.oid)
        """, [table_name])
        field_map = {line[0]: line[1:] for line in cursor.fetchall()}
        cursor.execute("SELECT * FROM %s LIMIT 1" % self.connection.ops.quote_name(table_name))
        return [
            FieldInfo(
                line.name,
                line.type_code,
                line.display_size,
                line.internal_size,
                line.precision,
                line.scale,
                *field_map[line.name],
            )
            for line in cursor.description
        ]

    def get_sequences(self, cursor, table_name, table_fields=()):
        cursor.execute("""
            SELECT s.relname as sequence_name, col.attname
            FROM pg_class s
                JOIN pg_namespace sn ON sn.oid = s.relnamespace
                JOIN pg_depend d ON d.refobjid = s.oid AND d.refclassid = 'pg_class'::regclass
                JOIN pg_attrdef ad ON ad.oid = d.objid AND d.classid = 'pg_attrdef'::regclass
                JOIN pg_attribute col ON col.attrelid = ad.adrelid AND col.attnum = ad.adnum
                JOIN pg_class tbl ON tbl.oid = ad.adrelid
                JOIN pg_namespace n ON n.oid = tbl.relnamespace
            WHERE s.relkind = 'S'
              AND d.deptype in ('a', 'n')
              AND n.nspname = 'public'
              AND tbl.relname = %s
        """, [table_name])
        return [
            {'name': row[0], 'table': table_name, 'column': row[1]}
            for row in cursor.fetchall()
        ]

    def get_relations(self, cursor, table_name):
        """
        Return a dictionary of {field_name: (field_name_other_table, other_table)}
        representing all relationships to the given table.
        """
        cursor.execute("""
            SELECT c2.relname, a1.attname, a2.attname
            FROM pg_constraint con
            LEFT JOIN pg_class c1 ON con.conrelid = c1.oid
            LEFT JOIN pg_class c2 ON con.confrelid = c2.oid
            LEFT JOIN pg_attribute a1 ON c1.oid = a1.attrelid AND a1.attnum = con.conkey[1]
            LEFT JOIN pg_attribute a2 ON c2.oid = a2.attrelid AND a2.attnum = con.confkey[1]
            WHERE c1.relname = %s AND con.contype = 'f'
        """, [table_name])
        return {row[1]: (row[2], row[0]) for row in cursor.fetchall()}

    def get_key_columns(self, cursor, table_name):
        cursor.execute("""
            SELECT kcu.column_name, ccu.table_name AS referenced_table, ccu.column_name AS referenced_column
            FROM information_schema.constraint_column_usage ccu
            LEFT JOIN information_schema.key_column_usage kcu
                ON ccu.constraint_catalog = kcu.constraint_catalog
                    AND ccu.constraint_schema = kcu.constraint_schema
                    AND ccu.constraint_name = kcu.constraint_name
            LEFT JOIN information_schema.table_constraints tc
                ON ccu.constraint_catalog = tc.constraint_catalog
                    AND ccu.constraint_schema = tc.constraint_schema
                    AND ccu.constraint_name = tc.constraint_name
            WHERE kcu.table_name = %s AND tc.constraint_type = 'FOREIGN KEY'
        """, [table_name])
        return cursor.fetchall()

    def get_constraints(self, cursor, table_name):
        """
        Retrieve any constraints or keys (unique, pk, fk, check, index) across
        one or more columns. Also retrieve the definition of expression-based
        indexes.
        """
        constraints = {}
        # Loop over the key table, collecting things as constraints. The column
        # array must return column names in the same order in which they were
        # created.
        cursor.execute("""
            SELECT
                c.conname,
                array(
                    SELECT attname
                    FROM unnest(c.conkey) WITH ORDINALITY cols(colid, arridx)
                    JOIN pg_attribute AS ca ON cols.colid = ca.attnum
                    WHERE ca.attrelid = c.conrelid
                    ORDER BY cols.arridx
                ),
                c.contype,
                (SELECT fkc.relname || '.' || fka.attname
                FROM pg_attribute AS fka
                JOIN pg_class AS fkc ON fka.attrelid = fkc.oid
                WHERE fka.attrelid = c.confrelid AND fka.attnum = c.confkey[1]),
                cl.reloptions
            FROM pg_constraint AS c
            JOIN pg_class AS cl ON c.conrelid = cl.oid
            JOIN pg_namespace AS ns ON cl.relnamespace = ns.oid
            WHERE ns.nspname = %s AND cl.relname = %s
        """, ["public", table_name])
        for constraint, columns, kind, used_cols, options in cursor.fetchall():
            constraints[constraint] = {
                "columns": columns,
                "primary_key": kind == "p",
                "unique": kind in ["p", "u"],
                "foreign_key": tuple(used_cols.split(".", 1)) if kind == "f" else None,
                "check": kind == "c",
                "index": False,
                "definition": None,
                "options": options,
            }
        # Now get indexes
        cursor.execute("""
            SELECT
                indexname, array_agg(attname ORDER BY arridx), indisunique, indisprimary,
                array_agg(ordering ORDER BY arridx), amname, exprdef, s2.attoptions
            FROM (
                SELECT
                    c2.relname as indexname, idx.*, attr.attname, am.amname,
                    CASE
                        WHEN idx.indexprs IS NOT NULL THEN
                            pg_get_indexdef(idx.indexrelid)
                    END AS exprdef,
                    CASE am.amname
                        WHEN 'btree' THEN
                            CASE (option & 1)
                                WHEN 1 THEN 'DESC' ELSE 'ASC'
                            END
                    END as ordering,
                    c2.reloptions as attoptions
                FROM (
                    SELECT *
                    FROM pg_index i, unnest(i.indkey, i.indoption) WITH ORDINALITY koi(key, option, arridx)
                ) idx
                LEFT JOIN pg_class c ON idx.indrelid = c.oid
                LEFT JOIN pg_class c2 ON idx.indexrelid = c2.oid
                LEFT JOIN pg_am am ON c2.relam = am.oid
                LEFT JOIN pg_attribute attr ON attr.attrelid = c.oid AND attr.attnum = idx.key
                WHERE c.relname = %s
            ) s2
            GROUP BY indexname, indisunique, indisprimary, amname, exprdef, attoptions;
        """, [table_name])
        for index, columns, unique, primary, orders, type_, definition, options in cursor.fetchall():
            if index not in constraints:
                basic_index = type_ == 'btree' and not index.endswith('_btree') and options is None
                constraints[index] = {
                    "columns": columns if columns != [None] else [],
                    "orders": orders if orders != [None] else [],
                    "primary_key": primary,
                    "unique": unique,
                    "foreign_key": None,
                    "check": False,
                    "index": True,
                    "type": Index.suffix if basic_index else type_,
                    "definition": definition,
                    "options": options,
                }
        return constraints