Database on the fly with scripting languages

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Question :

Database on the fly with scripting languages

I have a set of .csv files that I want to process. It would be far easier to process it with SQL queries. I wonder if there is some way to load a .csv file and use SQL language to look into it with a scripting language like python or ruby. Loading it with something similar to ActiveRecord would be awesome.

The problem is that I don’t want to have to run a database somewhere prior to running my script. I souldn’t have additionnal installations needed outside of the scripting language and some modules.

My question is which language and what modules should I use for this task. I looked around and can’t find anything that suits my need. Is it even possible?

Asked By: tmoisan


Answer #1:

There’s sqlite3, included into python. With it you can create a database (on memory) and add rows to it, and perform SQL queries.

If you want neat ActiveRecord-like functionality you should add an external ORM, like sqlalchemy. That’s a separate download though

Quick example using sqlalchemy:

from sqlalchemy import create_engine, Column, String, Integer, MetaData, Table
from sqlalchemy.orm import mapper, create_session
import csv
CSV_FILE = 'foo.csv'
engine = create_engine('sqlite://') # memory-only database

table = None
metadata = MetaData(bind=engine)
with open(CSV_FILE) as f:
    # assume first line is header
    cf = csv.DictReader(f, delimiter=',')
    for row in cf:
        if table is None:
            # create the table
            table = Table('foo', metadata, 
                Column('id', Integer, primary_key=True),
                *(Column(rowname, String()) for rowname in row.keys()))
        # insert data into the table

class CsvTable(object): pass
mapper(CsvTable, table)
session = create_session(bind=engine, autocommit=False, autoflush=True)

Now you can query the database, filtering by any field, etc.

Suppose you run the code above on this csv:

Afila Tun,32,afilatun
Foo Bar,33,baz

That will create and populate a table in memory with fields name, age, nickname. You can then query the table:

for r in session.query(CsvTable).filter(CsvTable.age == '32'):
    print, r.age, r.nickname

That will automatically create and run a SELECT query and return the correct rows.

Another advantage of using sqlalchemy is that, if you decide to use another, more powerful database in the future, you can do so pratically without changing the code.

Answered By: tmoisan

Answer #2:

Use a DB in a library like SQLite.
There are Python and Ruby versions .

Load your CSV into table, there might be modules/libraries to help you here too. Then SQL away.

Answered By: nosklo

Answer #3:

Looked at Perl and and Text::CSV and DBI? There are many modules on CPAN to do exactly this. Here is an example (from HERE):

use strict;
use warnings;
use DBI;

# Connect to the database, (the directory containing our csv file(s))

my $dbh = DBI->connect("DBI:CSV:f_dir=.;csv_eol=n;");

# Associate our csv file with the table name 'prospects'

$dbh->{'csv_tables'}->{'prospects'} = { 'file' => 'prospects.csv'};

# Output the name and contact field from each row

my $sth = $dbh->prepare("SELECT * FROM prospects WHERE name LIKE 'G%'");
while (my $row = $sth->fetchrow_hashref) {
     print("name = ", $row->{'Name'}, "  contact = ", $row->{'Contact'}. "n");

name = Glenhuntly Pharmacy  contact = Paul
name = Gilmour's Shoes  contact = Ringo

Just type perldoc DBI and perldoc Text::CSV at the command prompt for more.

Answered By: lexu

Answer #4:

CSV files are not databases–they have no indices–and any SQL simulation you imposed upon them would amount to little more than searching through the entire thing over and over again.

Answered By: dawg

Answer #5:

You could use either scripting language to parse the CSV file and store the data into SQLite, which just uses a single file for storage. From there you have it in a database and can run queries against it.

Alternatively, on windows you can setup an ODBC data source as a CSV file. But it may be difficult to automate this.

Answered By: Azeem.Butt

Answer #6:

I used nosklo’s solution (thanks!) but I already had a primary key (passed in as pk_col) within the column line (first line of csv). So I thought I’d share my modification. I used a ternary.

table = Table(tablename, metadata,
    *((Column(pk_col, Integer, primary_key=True)) if rowname == pk_col else (Column(rowname, String())) for rowname in row.keys()))
Answered By: Justin Ethier

Answer #7:

PHP FlatfileDB available here is a very good option if you are building a web app

Answered By: trash80

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