first prototype of migration script (#245)

terracotta/migrations/__init__.py

@@ -0,0 +1,17 @@
+"""migrations/__init__.py
+
+Define available migrations.
+"""
+
+import os
+import glob
+import importlib
+
+
+MIGRATIONS = {}
+
+for modname in glob.glob("v*_*.py", root_dir=os.path.dirname(__file__)):
+    mod = importlib.import_module(f"{__name__}.{modname[:-3]}")
+    assert all(hasattr(mod, attr) for attr in ("up_version", "down_version", "upgrade_sql", "downgrade_sql"))
+    assert mod.down_version not in MIGRATIONS
+    MIGRATIONS[mod.down_version] = mod

terracotta/migrations/v0_8.py

@@ -0,0 +1,13 @@
+
+
+up_version = (0, 8)
+down_version = (0, 7)
+
+upgrade_sql = [
+    # "CREATE TABLE",
+    # "ALTER TABLE keys ADD COLUMN index INTEGER UNIQUE",
+    # "ALTER TABLE keys RENAME TO key_names",
+    "UPDATE terracotta SET version='v0.8.0'",
+]
+
+downgrade_sql = []

terracotta/scripts/cli.py

@@ -69,6 +69,8 @@ def entrypoint() -> None:
 from terracotta.scripts.serve import serve
 cli.add_command(serve)
 
+from terracotta.scripts.migrate import migrate
+cli.add_command(migrate)
 
 if __name__ == '__main__':
     entrypoint()

terracotta/scripts/migrate.py

@@ -0,0 +1,72 @@
+"""scripts/migrate.py
+
+Migrate databases between Terracotta versions.
+"""
+
+from typing import Tuple
+
+import click
+import sqlalchemy as sqla
+
+from terracotta import get_driver, __version__
+from terracotta.migrations import MIGRATIONS
+
+
+def parse_version(verstr: str) -> Tuple[int]:
+    """Convert 'v<major>.<minor>.<patch>' to (major, minor, patch)"""
+    components = verstr.split(".")
+    components[0] = components[0].lstrip("v")
+    return tuple(int(c) for c in components[:3])
+
+
+def join_version(vertuple: Tuple[int]) -> str:
+    return "v" + ".".join(map(str, vertuple))
+
+
+@click.argument("DATABASE", required=True)
+@click.option("--from", "from_version", required=False, default=None)
+@click.option("--to", "to_version", required=False, default=__version__)
+@click.command("migrate")
+def migrate(database: str, to_version: str, from_version: str):
+    from_version, to_version, tc_version = (parse_version(v)[:2] if v else None for v in (from_version, to_version, __version__))
+
+    driver = get_driver(database)
+
+    # if to_version > tc_version:
+    #     raise ValueError(f"Unknown target version {join_version(to_version)} (this is {join_version(tc_version)}). Try upgrading terracotta.")
+
+    if from_version is None:
+        try:
+            with driver.connect(verify=False):
+                from_version = parse_version(driver.db_version)[:2]
+        except:
+            raise RuntimeError("Cannot determine database version.")
+
+    migration_chain = []
+    current_version = from_version
+
+    while current_version != to_version:
+        if current_version not in MIGRATIONS:
+            raise RuntimeError("Unexpected error")
+
+        migration = MIGRATIONS[current_version]
+        migration_chain.append(migration)
+        current_version = migration.up_version
+
+    click.echo("Upgrade path found\n")
+
+    for migration in migration_chain:
+        click.echo(f"{join_version(migration.down_version)} -> {join_version(migration.up_version)}")
+
+        for cmd in migration.upgrade_sql:
+            click.echo(f"    {cmd}")
+
+        click.echo("")
+
+    click.echo(f"This will upgrade the database from {join_version(from_version)} -> {join_version(to_version)} and execute the above SQL commands.")
+    click.confirm("Continue?", abort=True)
+
+    with driver.connect(verify=False):
+        for migration in migration_chain:
+            for cmd in migration.upgrade_sql:
+                driver.meta_store.connection.execute(sqla.text(cmd))