Dialect-specific SQLAlchemy declarative Column defaults

examples.py

class Table1(Base):
    __tablename__ = 'table1'
    id = sa.Column(UUID, primary_key=True, server_default=sa.text("uuid_generate_v4()"))

    
class Table2(Base):
    __tablename__ = 'table2'
    id = sa.Column(UUID, primary_key=True, default=uuid.uuid4)

utils.py

import uuid
from sqlalchemy import text
from sqlalchemy.schema import ColumnDefault, DefaultClause
from sqlalchemy.ext.compiler import compiles


@compiles(UUID, "sqlite")
def compile_uuid_sqlite(type_, compiler, **kwargs):
    expr = kwargs.get("type_expression")
    if expr is not None and expr.primary_key and expr.server_default and not expr.default:
        expr.server_default = None
        expr.default = ColumnDefault(uuid.uuid4)
    return compiler.visit_CHAR(type_, **kwargs)


@compiles(UUID, "postgresql")
def compile_uuid_postgresql(type_, compiler, **kwargs):
    expr = kwargs.get("type_expression")
    if expr is not None and expr.primary_key and expr.default and not expr.server_default:
        expr.server_default = DefaultClause(text("uuid_generate_v4()"))
        expr.default = None
    return compiler.visit_UUID(type_, **kwargs)