return SQL table as JSON in python

Question

I'm playing around with a little web app in web.py, and am setting up a url to return a JSON object. What's the best way to convert a SQL table to JSON using python?

Answer 1

Here is a really nice example of a pythonic way to do that:

import json
import psycopg2

def db(database_name='pepe'):
    return psycopg2.connect(database=database_name)

def query_db(query, args=(), one=False):
    cur = db().cursor()
    cur.execute(query, args)
    r = [dict((cur.description[i][0], value) \
               for i, value in enumerate(row)) for row in cur.fetchall()]
    cur.connection.close()
    return (r[0] if r else None) if one else r

my_query = query_db("select * from majorroadstiger limit %s", (3,))

json_output = json.dumps(my_query)

You get an array of JSON objects:

>>> json_output
'[{"divroad": "N", "featcat": null, "countyfp": "001",...

Or with the following:

>>> j2 = query_db("select * from majorroadstiger where fullname= %s limit %s",\
 ("Mission Blvd", 1), one=True)

you get a single JSON object:

>>> j2 = json.dumps(j2)
>>> j2
'{"divroad": "N", "featcat": null, "countyfp": "001",...

Answer 2

import sqlite3
import json

DB = "./the_database.db"

def get_all_users( json_str = False ):
    conn = sqlite3.connect( DB )
    conn.row_factory = sqlite3.Row # This enables column access by name: row['column_name'] 
    db = conn.cursor()

    rows = db.execute('''
    SELECT * from Users
    ''').fetchall()

    conn.commit()
    conn.close()

    if json_str:
        return json.dumps( [dict(ix) for ix in rows] ) #CREATE JSON

    return rows

Callin the method no json...

print get_all_users()

prints:

[(1, u'orvar', u'password123'), (2, u'kalle', u'password123')]

Callin the method with json...

print get_all_users( json_str = True )

prints:

[{"password": "password123", "id": 1, "name": "orvar"}, {"password": "password123", "id": 2, "name": "kalle"}]

Answer 3

Personally I prefer SQLObject for this sort of thing. I adapted some quick-and-dirty test code I had to get this:

import simplejson

from sqlobject import *

# Replace this with the URI for your actual database
connection = connectionForURI('sqlite:/:memory:')
sqlhub.processConnection = connection

# This defines the columns for your database table. See SQLObject docs for how it
# does its conversions for class attributes <-> database columns (underscores to camel
# case, generally)

class Song(SQLObject):

    name = StringCol()
    artist = StringCol()
    album = StringCol()

# Create fake data for demo - this is not needed for the real thing
def MakeFakeDB():
    Song.createTable()
    s1 = Song(name="B Song",
              artist="Artist1",
              album="Album1")
    s2 = Song(name="A Song",
              artist="Artist2",
              album="Album2")

def Main():
    # This is an iterable, not a list
    all_songs = Song.select().orderBy(Song.q.name)

    songs_as_dict = []

    for song in all_songs:
        song_as_dict = {
            'name' : song.name,
            'artist' : song.artist,
            'album' : song.album}
        songs_as_dict.append(song_as_dict)

    print simplejson.dumps(songs_as_dict)


if __name__ == "__main__":
    MakeFakeDB()
    Main()

Answer 4

More information about how you'll be working with your data before transferring it would help a ton. The json module provides dump(s) and load(s) methods that'll help if you're using 2.6 or newer: http://docs.python.org/library/json.html.

-- EDITED --

Without knowing which libraries you're using I can't tell you for sure if you'll find a method like that. Normally, I'll process query results like this (examples with kinterbasdb because it's what we're currently working with):

qry = "Select Id, Name, Artist, Album From MP3s Order By Name, Artist"
# Assumes conn is a database connection.
cursor = conn.cursor()
cursor.execute(qry)
rows = [x for x in cursor]
cols = [x[0] for x in cursor.description]
songs = []
for row in rows:
  song = {}
  for prop, val in zip(cols, row):
    song[prop] = val
  songs.append(song)
# Create a string representation of your array of songs.
songsJSON = json.dumps(songs)

There are undoubtedly better experts out there who'll have list comprehensions to eliminate the need for written out loops, but this works and should be something you could adapt to whatever library you're retrieving records with.

Answer 5

I knocked together a short script that dumps all data from all tables, as dicts of column name : value. Unlike other solutions, it doesn't require any info about what the tables or columns are, it just finds everything and dumps it. Hope someone finds it useful!

from contextlib import closing
from datetime import datetime
import json
import MySQLdb
DB_NAME = 'x'
DB_USER = 'y'
DB_PASS = 'z'

def get_tables(cursor):
    cursor.execute('SHOW tables')
    return [r[0] for r in cursor.fetchall()] 

def get_rows_as_dicts(cursor, table):
    cursor.execute('select * from {}'.format(table))
    columns = [d[0] for d in cursor.description]
    return [dict(zip(columns, row)) for row in cursor.fetchall()]
 
def dump_date(thing):
    if isinstance(thing, datetime):
        return thing.isoformat()
    return str(thing)


with closing(MySQLdb.connect(user=DB_USER, passwd=DB_PASS, db=DB_NAME)) as conn, closing(conn.cursor()) as cursor:
    dump = {
        table: get_rows_as_dicts(cursor, table)
        for table in get_tables(cursor)
    }
    print(json.dumps(dump, default=dump_date, indent=2))

Answer 6

nobody seem to have offered the option to get the JSON directly from the Postgresql server, using the postgres JSON capability https://www.postgresql.org/docs/9.4/static/functions-json.html

No parsing, looping or any memory consumption on the python side, which you may really want to consider if you're dealing with 100,000's or millions of rows.

from django.db import connection

sql = 'SELECT to_json(result) FROM (SELECT * FROM TABLE table) result)'
with connection.cursor() as cursor:
  cursor.execute(sql)
  output = cursor.fetchall()

a table like:

id, value
----------
1     3
2     7

will return a Python JSON Object

[{"id": 1, "value": 3},{"id":2, "value": 7}]

Then use json.dumps to dump as a JSON string

Answer 7

Most simple way,

use json.dumps but if its datetime will require to parse datetime into json serializer.

here is mine,

import MySQLdb, re, json
from datetime import date, datetime

def json_serial(obj):
    """JSON serializer for objects not serializable by default json code"""

    if isinstance(obj, (datetime, date)):
        return obj.isoformat()
    raise TypeError ("Type %s not serializable" % type(obj))

conn = MySQLdb.connect(instance)
curr = conn.cursor()
curr.execute("SELECT * FROM `assets`")
data = curr.fetchall()
print json.dumps(data, default=json_serial)

it will return json dump

one more simple method without json dumps, here get header and use zip to map with each finally made it as json but this is not change datetime into json serializer...

data_json = []
header = [i[0] for i in curr.description]
data = curr.fetchall()
for i in data:
    data_json.append(dict(zip(header, i)))
print data_json

Answer 8

I would supplement The Demz answer with the psycopg2 version:

import psycopg2 
import psycopg2.extras
import json
connection = psycopg2.connect(dbname=_cdatabase, host=_chost, port=_cport , user=_cuser, password=_cpassword)
cursor = connection.cursor(cursor_factory=psycopg2.extras.DictCursor) # This line allows dictionary access.
#select some records into "rows"
jsonout= json.dumps([dict(ix) for ix in rows])

Answer 9

For sqlite, it is possible to set a callable to connection.row_factory and change the format of query results to python dictionary object. See the documentation. Here is an example:

import sqlite3, json

def dict_factory(cursor, row):
    d = {}
    for idx, col in enumerate(cursor.description):
        # col[0] is the column name
        d[col[0]] = row[idx]
    return d

def get_data_to_json():
    conn = sqlite3.connect("database.db")
    conn.row_factory = dict_factory
    c = conn.cursor()
    c.execute("SELECT * FROM table")
    rst = c.fetchall() # rst is a list of dict
    return jsonify(rst)

Answer 10

I'm Sorry to inform that the above code will fail to export date time fields in json. It will appear like this:

....
, 'TimeCreated': datetime.datetime(2019, 6, 17, 9, 2, 17), 'Created': 1,
....

Which make the output an invalid json.

Answer 11

If you are using an MSSQL Server 2008 and above, you can perform your SELECT query to return json by using the FOR JSON AUTO clause E.G

SELECT name, surname FROM users FOR JSON AUTO

Will return Json as

[{"name": "Jane","surname": "Doe" }, {"name": "Foo","surname": "Samantha" }, ..., {"name": "John", "surname": "boo" }]

Answer 12

After 10 years :) . Without list comprehension

Return a single row of values from a select query like below.

"select name,userid, address from table1 where userid = 1"

json output

{ name : "name1", userid : 1, address : "adress1, street1" }

Code

cur.execute(f"select name,userid, address from table1 where userid = 1 ")
row = cur.fetchone()
desc = list(zip(*cur.description))[0]  #To get column names
rowdict = dict(zip(desc,row))
jsondict = jsonify(rowdict)  #Flask jsonify

cur.description is a tuple of tuples as below. unzip and zip to combine column name with values

(('name', None, None, None, None, None, None), ('userid', None, None, None, None, None, None), ('address', None, None, None, None, None, None))

Answer 13

from sqlalchemy import Column
from sqlalchemy import Integer
from sqlalchemy import String

Base = declarative_base()
metadata = Base.metadata


class UserTable(Base):
    __tablename__ = 'UserTable'

    Id = Column("ID", Integer, primary_key=True)
    Name = Column("Name", String(100))

        
class UserTableDTO:
    def __init__(self, ob):
        self.Id = ob.Id
        self.Name = ob.Name
        
rows = dbsession.query(Table).all()

json_string = [json.loads(json.dumps(UserTableDTO(ob).__dict__, default=lambda x: str(x)))for ob in rows]
print(json_string)

Answer 14

One simple example for return SQL table as formatted JSON and fix error as he had @Whitecat

I get the error datetime.datetime(1941, 10, 31, 0, 0) is not JSON serializable

In that example you should use JSONEncoder.

import json
import pymssql

# subclass JSONEncoder
class DateTimeEncoder(JSONEncoder):
        #Override the default method
        def default(self, obj):
            if isinstance(obj, (datetime.date, datetime.datetime)):
                return obj.isoformat()

def mssql_connection():
    try:
        return pymssql.connect(server="IP.COM", user="USERNAME", password="PASSWORD", database="DATABASE")
    except Exception:
        print("\nERROR: Unable to connect to the server.")
        exit(-1)

def query_db(query):
    cur = mssql_connection().cursor()
    cur.execute(query)
    r = [dict((cur.description[i][0], value) for i, value in enumerate(row)) for row in cur.fetchall()]
    cur.connection.close()
    return r

def write_json(query_path):
    # read sql from file
    with open("../sql/my_sql.txt", 'r') as f:
        sql = f.read().replace('\n', ' ')
    # creating and writing to a json file and Encode DateTime Object into JSON using custom JSONEncoder
    with open("../output/my_json.json", 'w', encoding='utf-8') as f:
        json.dump(query_db(sql), f, ensure_ascii=False, indent=4, cls=DateTimeEncoder) 

if __name__ == "__main__":
    write_json()

# You get formatted my_json.json, for example:
[
   {
      "divroad":"N",
      "featcat":null,
      "countyfp":"001",
      "date":"2020-08-28"
   }
]

Answer 15

This simple code worked for me in Flask api:

@app.route('/output/json/') 
def outputJson():
    conn = sqlite3.connect('database.db')
    conn.row_factory = sqlite3.Row
    temp = conn.execute('SELECT * FROM users').fetchall()
    conn.close()
    result = [{k: item[k] for k in item.keys()} for item in temp]
    return jsonify(result)