Schema¶
The PostgresSchema()
class provides basic schema management functionality.
Django does NOT support custom schemas. This module does not attempt to solve that problem.
This module merely allows you to create/drop schemas and allow you to execute raw SQL in a schema. It is not attempt at bringing multi-schema support to Django.
Reference an existing schema¶
for psqlextra.schema import PostgresSchema
schema = PostgresSchema("myschema")
with schema.connection.cursor() as cursor:
cursor.execute("SELECT * FROM tablethatexistsinmyschema")
Checking if a schema exists¶
for psqlextra.schema import PostgresSchema
schema = PostgresSchema("myschema")
if PostgresSchema.exists("myschema"):
print("exists!")
else:
print('does not exist!")
Creating a new schema¶
With a custom name¶
for psqlextra.schema import PostgresSchema
# will raise an error if the schema already exists
schema = PostgresSchema.create("myschema")
Re-create if necessary with a custom name¶
Warning
If the schema already exists and it is non-empty or something is referencing it, it will NOT be dropped. Specify cascade=True
to drop all of the schema’s contents and anything referencing it.
for psqlextra.schema import PostgresSchema
# will drop existing schema named `myschema` if it
# exists and re-create it
schema = PostgresSchema.drop_and_create("myschema")
# will drop the schema and cascade it to its contents
# and anything referencing the schema
schema = PostgresSchema.drop_and_create("otherschema", cascade=True)
With a time-based name¶
Warning
The time-based suffix is precise up to the second. If two threads or processes both try to create a time-based schema name with the same suffix in the same second, they will have conflicts.
for psqlextra.schema import PostgresSchema
# schema name will be "myprefix_<timestamp>"
schema = PostgresSchema.create_time_based("myprefix")
print(schema.name)
With a random name¶
A 8 character suffix is appended. Entropy is dependent on your system. See urandom()
for more information.
for psqlextra.schema import PostgresSchema
# schema name will be "myprefix_<8 random characters>"
schema = PostgresSchema.create_random("myprefix")
print(schema.name)
Temporary schema with random name¶
Use the postgres_temporary_schema()
context manager to create a schema with a random name. The schema will only exist within the context manager.
By default, the schema is not dropped if an exception occurs in the context manager. This prevents unexpected data loss. Specify drop_on_throw=True
to drop the schema if an exception occurs.
Without an outer transaction, the temporary schema might not be dropped when your program is exits unexpectedly (for example; if it is killed with SIGKILL). Wrap the creation of the schema in a transaction to make sure the schema is cleaned up when an error occurs or your program exits suddenly.
Warning
By default, the drop will fail if the schema is not empty or there is anything referencing the schema. Specify cascade=True
to drop all of the schema’s contents and anything referencing it.
for psqlextra.schema import postgres_temporary_schema
with postgres_temporary_schema("myprefix") as schema:
pass
with postgres_temporary_schema("otherprefix", drop_on_throw=True) as schema:
raise ValueError("drop it like it's hot")
with postgres_temporary_schema("greatprefix", cascade=True) as schema:
with schema.connection.cursor() as cursor:
cursor.execute(f"CREATE TABLE {schema.name} AS SELECT 'hello'")
with postgres_temporary_schema("amazingprefix", drop_on_throw=True, cascade=True) as schema:
with schema.connection.cursor() as cursor:
cursor.execute(f"CREATE TABLE {schema.name} AS SELECT 'hello'")
raise ValueError("oops")
Deleting a schema¶
Any schema can be dropped, including ones not created by PostgresSchema
.
The public
schema cannot be dropped. This is a Postgres built-in and it is almost always a mistake to drop it. A SuspiciousOperation
erorr will be raised if you attempt to drop the public
schema.
Warning
By default, the drop will fail if the schema is not empty or there is anything referencing the schema. Specify cascade=True
to drop all of the schema’s contents and anything referencing it.
for psqlextra.schema import PostgresSchema
schema = PostgresSchema.drop("myprefix")
schema = PostgresSchema.drop("myprefix", cascade=True)