format CREATE TABLE query with list of identifiers

Question

I want to write a script in Python that creates a PostgreSQL table from a CSV. Instead of using psycopg2.copy_from I want something more personal and more flexible.

Obviously, I am going to read the first row of the CSV file and get a list of column names from it. Then I want to transform this list into the list of columns that you would write when creating a table in postgreSQL :

"column_name_1" text,
"column_name_2" text,
"column_name_3" text,
...
"column_name_N" text

(by default, I want all my columns to have the type text ; I may change these types later).
Note that I DO want the double quotes around the column names to appear, since these column names may contain spaces or accented characters.

I tried to use psycopg2.sql.Identifier to put double quotes around my column names, but it fails since I want to concatenate these identifiers with “text”…

Here is what I tried so far:

import psycopg2
import csv 

conn = psycopg2.connect(
                            dbname = "spatialDB",host="localhost",
                            port = 5432, user = "postgres",
                            password="postgres"
                            )

cur = conn.cursor()

FileName = "csv_to_import.csv"
file = open(FileName,'r',encoding='utf-8')
reader = csv.reader(file,delimiter=";")

columns = next(reader)

# The line below is what I wanted to do, but you cannot concatenate 
# an SQL identifier with a string 

#column_types = [psycopg2.sql.Identifier(c) + " text" for c in colums]

# This is what I did instead but it's ugly
column_types = [""" + c + ""  text" for c in columns]

schema = "myschema"
table_name = "import_csv_python"

model_query = "CREATE TABLE {0}.{1}({2});" 
column_list = ",".join(column_types)

query = model_query.format(schema,table_name,column_list)


cur.execute(query)
file.close()
cur.close()
conn.commit()

How would you correct this code to make it use the psycopg2.sql.Identifier function, to properly quote the column names? (the same question goes for the parameters {0} and {1}, which are respectively the schema and the table name)

Asked By: R. Bourgeon

||

Source

Answer 1

Use the method as_string(context) to build the columns list and convert all string arguments to Composable:

import psycopg2.sql as sql

column_types = [sql.Identifier(c).as_string(cur) + " text" for c in columns]

schema = sql.Identifier("myschema")
table_name = sql.Identifier("import_csv_python")

model_query = sql.SQL("CREATE TABLE {0}.{1}({2});") 
column_list = sql.SQL(",".join(column_types))

query = model_query.format(schema,table_name,column_list)

Answered By: klin

format CREATE TABLE query with list of identifiers

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