PostgreSQL Recipes

Authenticate with a username and password

Recipe source: postgresql_authenticate.py

To connect to a PostgreSQL database, the username and password must be provided in the URI. For example,

postgresql://username:password@hostname:port/dbname

See the PostgreSQL documentation for full details.

import os

import adbc_driver_postgresql.dbapi

uri = os.environ["ADBC_POSTGRESQL_TEST_URI"]
conn = adbc_driver_postgresql.dbapi.connect(uri)

with conn.cursor() as cur:
    cur.execute("SELECT 1")
    assert cur.fetchone() == (1,)

conn.close()

Create/append to a table from an Arrow table

Recipe source: postgresql_create_append_table.py

ADBC allows creating and appending to database tables using Arrow tables.

import os

import pyarrow

import adbc_driver_postgresql.dbapi

uri = os.environ["ADBC_POSTGRESQL_TEST_URI"]
conn = adbc_driver_postgresql.dbapi.connect(uri)

For the purposes of testing, we’ll first make sure the table doesn’t exist.

with conn.cursor() as cur:
    cur.execute("DROP TABLE IF EXISTS example")

Now we can create the table.

with conn.cursor() as cur:
    data = pyarrow.table(
        [
            [1, 2, None, 4],
        ],
        schema=pyarrow.schema(
            [
                ("ints", "int32"),
            ]
        ),
    )
    cur.adbc_ingest("example", data, mode="create")

conn.commit()

After ingestion, we can fetch the result.

with conn.cursor() as cur:
    cur.execute("SELECT * FROM example")
    assert cur.fetchone() == (1,)
    assert cur.fetchone() == (2,)

    cur.execute("SELECT COUNT(*) FROM example")
    assert cur.fetchone() == (4,)

If we try to ingest again, it’ll fail, because the table already exists.

with conn.cursor() as cur:
    try:
        cur.adbc_ingest("example", data, mode="create")
    except conn.ProgrammingError:
        pass
    else:
        raise RuntimeError("Should have failed!")

Instead, we can append to the table.

with conn.cursor() as cur:
    cur.adbc_ingest("example", data, mode="append")

    cur.execute("SELECT COUNT(*) FROM example")
    assert cur.fetchone() == (8,)

conn.close()

Execute a statement with bind parameters

Recipe source: postgresql_execute_bind.py

ADBC allows using Python and Arrow values as bind parameters. Right now, the PostgreSQL driver only supports bind parameters for queries that don’t generate result sets.

import os

import pyarrow

import adbc_driver_postgresql.dbapi

uri = os.environ["ADBC_POSTGRESQL_TEST_URI"]
conn = adbc_driver_postgresql.dbapi.connect(uri)

We’ll create an example table to test.

with conn.cursor() as cur:
    cur.execute("DROP TABLE IF EXISTS example")
    cur.execute("CREATE TABLE example (ints INT, bigints BIGINT)")

conn.commit()

We can bind Python values:

with conn.cursor() as cur:
    cur.executemany("INSERT INTO example VALUES ($1, $2)", [(1, 2), (3, 4)])

    cur.execute("SELECT SUM(ints) FROM example")
    assert cur.fetchone() == (4,)

Note

If you’re used to the format-string style %s syntax that libraries like psycopg use for bind parameters, note that this is not supported—only the PostgreSQL-native $1 syntax.

We can also bind Arrow values:

with conn.cursor() as cur:
    data = pyarrow.record_batch(
        [
            [5, 6],
            [7, 8],
        ],
        names=["$1", "$2"],
    )
    cur.executemany("INSERT INTO example VALUES ($1, $2)", data)

    cur.execute("SELECT SUM(ints) FROM example")
    assert cur.fetchone() == (15,)

conn.close()

Get the Arrow schema of a table

Recipe source: postgresql_get_table_schema.py

ADBC lets you get the schema of a table as an Arrow schema.

import os

import pyarrow

import adbc_driver_postgresql.dbapi

uri = os.environ["ADBC_POSTGRESQL_TEST_URI"]
conn = adbc_driver_postgresql.dbapi.connect(uri)

We’ll create an example table to test.

with conn.cursor() as cur:
    cur.execute("DROP TABLE IF EXISTS example")
    cur.execute("CREATE TABLE example (ints INT, bigints BIGINT)")

conn.commit()

assert conn.adbc_get_table_schema("example") == pyarrow.schema(
    [
        ("ints", "int32"),
        ("bigints", "int64"),
    ]
)

conn.close()

List catalogs, schemas, and tables

Recipe source: postgresql_list_catalogs.py

ADBC allows listing tables, catalogs, and schemas in the database.

import os

import adbc_driver_postgresql.dbapi

uri = os.environ["ADBC_POSTGRESQL_TEST_URI"]
conn = adbc_driver_postgresql.dbapi.connect(uri)

We’ll create an example table to look for.

with conn.cursor() as cur:
    cur.execute("DROP TABLE IF EXISTS example")
    cur.execute("CREATE TABLE example (ints INT, bigints BIGINT)")

conn.commit()

The data is given as a PyArrow RecordBatchReader.

objects = conn.adbc_get_objects(depth="all").read_all()

We’ll convert it to plain Python data for convenience.

objects = objects.to_pylist()
catalog = objects[0]
assert catalog["catalog_name"] == "postgres"

db_schema = catalog["catalog_db_schemas"][0]
assert db_schema["db_schema_name"] == "public"

tables = db_schema["db_schema_tables"]
example = [table for table in tables if table["table_name"] == "example"]
assert len(example) == 1
example = example[0]

assert example["table_columns"][0]["column_name"] == "ints"
assert example["table_columns"][1]["column_name"] == "bigints"

conn.close()