From 1b81a8d08e9faf5fa653094d89e2ae6767559f98 Mon Sep 17 00:00:00 2001 From: Andreas Motl Date: Mon, 6 Mar 2023 02:59:37 +0100 Subject: [PATCH] SQLAlchemy: Add support for `Column(server_default=...)` Makes the `CrateDDLCompiler` honour the `server_default` option. --- examples/column_server_default.py | 123 ++++++++++++++++++++++++++++++ 1 file changed, 123 insertions(+) create mode 100644 examples/column_server_default.py diff --git a/examples/column_server_default.py b/examples/column_server_default.py new file mode 100644 index 00000000..d64c1e7b --- /dev/null +++ b/examples/column_server_default.py @@ -0,0 +1,123 @@ +""" +Introduction +============ + +CrateDB's `NOW()` can be used like this to auto-generate timestamp values:: + + crash <>> import sqlalchemy as sa + >>> sa.Column("timestamp", sa.DateTime, server_default=sa.text("NOW()")) + +-- https://docs.sqlalchemy.org/en/20/core/metadata.html#sqlalchemy.schema.Column.params.server_default + +""" +import re +import sys +from functools import lru_cache + +import sqlalchemy as sa + + +class ColumnServerDefaultExample: + def __init__(self, dsn: str): + self.dsn = dsn + + @property + @lru_cache + def engine(self): + return sa.create_engine(self.dsn, echo=True) + + @property + @lru_cache + def table(self): + metadata = sa.MetaData() + if self.is_cratedb: + return sa.Table( + "testdrive", + metadata, + sa.Column("timestamp", sa.DateTime, server_default=sa.text("NOW()")), + sa.Column("value", sa.Float), + ) + else: + raise ValueError("Unknown database type") + + @property + def is_postgresql(self): + return self.match_dsn("postgresql") + + @property + def is_cratedb(self): + return self.match_dsn("crate") + + def match_dsn(self, prefix: str): + return re.match(rf"^{prefix}(?:\+\w+?)?://", self.dsn) + + def create(self): + self.table.drop(bind=self.engine, checkfirst=True) + self.table.create(bind=self.engine) + + def insert(self): + stmt = self.table.insert().values(value=42.42) + with self.engine.begin() as session: + session.execute(stmt) + session.execute(stmt) + + def read(self): + with self.engine.begin() as session: + if self.is_cratedb: + session.execute(sa.text("REFRESH TABLE testdrive;")) + result = session.execute(sa.text("SELECT * FROM testdrive;")) + print("result:", result.fetchall()) + + def reflect(self): + meta = sa.MetaData() + reflected_table = sa.Table("testdrive", meta, autoload_with=self.engine) + print(reflected_table) + print(reflected_table.columns) + print(reflected_table.constraints) + print(reflected_table.primary_key) + + +if __name__ == "__main__": + + kind = sys.argv[1] + if kind == "cratedb": + DSN = "crate://localhost:4200" + else: + raise ValueError("Unknown kind") + + ex = ColumnServerDefaultExample(DSN) + ex.create() + ex.insert() + ex.read() + # ex.reflect() pFad - Phonifier reborn

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