MySQL ADBC driver ignores the target schema when creating an ingest table #258

Summary

The ADBC Driver Foundry's MySQL driver (0.6.1, the latest release at the time of writing) ignores the target schema when it creates the table for an ingest. Given db_schema_name, it creates the table in the connection's default database, then inserts into the target database, so the ingest fails.

#255 works around this in the ADBC adapter. This issue tracks the workaround until the driver is fixed.

Reproduction

MySQL 8.4.11, adbc-driver-manager 1.12.0, MySQL driver 0.6.1 (dbc install mysql):

import pyarrow as pa
from adbc_driver_manager import dbapi

con = dbapi.connect(driver="mysql", db_kwargs={"uri": "mysql://root@127.0.0.1:3306/xql"})
with con.cursor() as cur:
    cur.execute("CREATE DATABASE IF NOT EXISTS era5")
    cur.adbc_ingest("surface", pa.table({"x": [1.0]}), mode="create", db_schema_name="era5")

• Expected: a table era5.surface holding one row.

• Actual:

  ProgrammingError: NOT_FOUND: [MySQL] failed to prepare batch insert statement:
  Error 1146 (42S02): Table 'era5.surface' doesn't exist.
  

  The table was created as xql.surface, in the connection's default database, according to information_schema.tables.

Workaround in xarray-sql

For MySQL and MariaDB, xarray_sql/backends/adbc.py doesn't pass db_schema_name at all. Instead, _default_database makes the target database the connection's default (USE era5) for the duration of the ingest, then restores the previous default. MySQL can't unset a default database, so a connection that had no default keeps the target afterwards.

This is how mixed-dimension Datasets register as era5.<group> on MySQL. test_mysql_mixed_dimensions_register_in_a_database covers it; the test runs when XARRAY_SQL_TEST_MYSQL_URI is set.

Next steps

• Report upstream at adbc-drivers/mysql (no existing issue covered it at the time of writing).
• Once a fixed driver is released, remove _default_database and pass db_schema_name through on MySQL, as on every other database.

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