Graceful Primary Key Error handling in Python/psycopg2

Question

Using Python 2.7 and

In [150]: psycopg2.version Out[150]: \'2.4.2 (dt dec pq3 ext)\'

I have a simple python scripts that processing transaction

Answer 1

You should rollback transaction on error.

I've added one more try..except..else construction in the code bellow to show the exact place where exception will occur.

try:
    cur = conn.cursor()

    try:
        cur.execute("""insert into encounter_id_table (
            encounter_id,current_date  )
            values       
            (%(create_date)s, %(encounter_id)s ) ;""",
            'encounter_id':i.split('~')[1],  
            'create_date': datetime.date.today() })
    except psycopg2.IntegrityError:
        conn.rollback()
    else:
        conn.commit()

    cur.close() 
except Exception , e:
    print 'ERROR:', e[0]

Answer 2

First of all: CURRENT_DATE is a reserved word in every SQL standard as well as in PostgreSQL. You cannot use it as identifier without double-quoting it. I would strongly advice not to use it at all. I renamed the column to curdate in my example

Next, I am no expert in python syntax, but you seem to have reversed the order of your insert-columns:

(%(create_date)s, %(encounter_id)s )

Should be:

( %(encounter_id)s, %(create_date)s)

To your main question: you can avoid the problem altogether by checking if the key is already in the table before using it in the insert command:

INSERT INTO encounter_id_table (encounter_id, curdate)
SELECT 1234, now()::date
WHERE  NOT EXISTS (SELECT * FROM encounter_id_table t
                   WHERE t.encounter_id = 1234);

In Python syntax, that should be:

cur.execute("""INSERT INTO encounter_id_table (encounter_id, curdate)
    SELECT %(encounter_id)s, %(create_date)s,
    WHERE  NOT EXISTS (
           SELECT * FROM encounter_id_table t
           WHERE t.encounter_id = %(encounter_id)s);""",
  {'encounter_id':i.split('~')[1],  
  'create_date': datetime.date.today()})