How do I COPY IMPORT a json file into postgres?

Question

I would like to import json data into postgres. The data I have is of the orders of a million rows, sizes are a minimum of 700 MB and stretches till 3 GB.

Here's a sample data I created based on the structure of data I have. I tried importing this into postgres but I get an error.

Sample(1) data

{"offers":{"offer":[
{"url": "https://some1-value.com", "nested": {"id":4,"value":"some1 text value"}, "quotes": "5\"  side"},
{"url": "https://some2-value.com", "nested": {"id":5,"value":"some2 text value"}, "quotes": "6\"  side"},
{"url": "https://some3-value.com", "nested": {"id":6,"value":"some3 text value"}, "quotes": "7\"  side"}]}}

Command I used and the error I got

# copy contrial from '/home/ubuntu/sample-data.json';
ERROR:  invalid input syntax for type json
DETAIL:  The input string ended unexpectedly.
CONTEXT:  JSON data, line 1: {"offers":{"offer":[
COPY contrial, line 1, column info: "{"offers":{"offer":["

I modified the file to remove the first two keys and have just a list of jsons like below, but I still get an error.

Sample(2) data

[
{"url": "https://some1-value.com", "nested": {"id":4,"value":"some1 text value"}, "quotes": "5\"  side"},
{"url": "https://some2-value.com", "nested": {"id":5,"value":"some2 text value"}, "quotes": "6\"  side"},
{"url": "https://some3-value.com", "nested": {"id":6,"value":"some3 text value"}, "quotes": "7\"  side"}]

Error

# copy contrial from '/home/ubuntu/sample2-data.json';
ERROR:  invalid input syntax for type json
DETAIL:  The input string ended unexpectedly.
CONTEXT:  JSON data, line 1: [
COPY contrial, line 1, column info: "["

Sample(3) data I modified further

[{"url": "https://some1-value.com", "nested": {"id":4,"value":"some1 text value"}, "quotes": "5\"  side"},
{"url": "https://some2-value.com", "nested": {"id":5,"value":"some2 text value"}, "quotes": "6\"  side"},
{"url": "https://some3-value.com", "nested": {"id":6,"value":"some3 text value"}, "quotes": "7\"  side"}]

Different Error

# copy contrial from '/home/ubuntu/sample2-data.json';
ERROR:  invalid input syntax for type json
DETAIL:  Token "side" is invalid.
CONTEXT:  JSON data, line 1: ...,"value":"some1 text value"}, "quotes": "5"  side...
COPY contrial, line 1, column info: "[{"url": "https://some1-value.com", "nested": {"id":4,"value":"some1 text value"}, "quotes": "5"  si..."

Create table statement

CREATE TABLE public.contrial (
    info json NOT NULL
);

The end goal is to create a table with keys as columns and values as records. Nested keys would need to be flattened.

+-------------------------+-----------+------------------+----------+
| url                     | nested_id | nested_value     | quotes   |
+-------------------------+-----------+------------------+----------+
| https://some1-value.com | 4         | some1 text value | 5\" side |
+-------------------------+-----------+------------------+----------+
| https://some2-value.com | 5         | some2 text value | 6\" side |
+-------------------------+-----------+------------------+----------+
| https://some3-value.com | 6         | some3 text value | 7\" side |
+-------------------------+-----------+------------------+----------+

scientific_explorer · Accepted Answer · 2021-08-19 07:21:28Z

I ended up using Andre Dunstan's blog and this SO answer which says to format the json in a specific way to use the copy command.

Since my structure is pretty defined for the files I'm parsing, I ended up with the following script.

def file_len(fname):
    # to find the number of lines in the file.
    # Has been pretty efficient even for millions of records
    with open(fname) as f:
        for i, l in enumerate(f):
            pass
    return i + 1

INPUTFILE = '/path/to/input.json'
OUTPUTFILE = '/path/to/output.json.csv'
LEN = file_len(INPUTFILE)
with open(OUTPUTFILE, 'w') as fo:
    with open(INPUTFILE, 'r') as fi:
        for i, l in enumerate(fi):
            # I skip the first line
            if i == 0: continue 
            
            # To remove the ']}}' from the end
            elif i+1 == LEN: _ = fo.write(l[:-3])
            
            # To remove the ',' from the end 
            # and add \n since write does not add newline on its own
            else: _ = fo.write(l[:-2]+'\n') 

# load statement

import sqlalchemy
POSTGRESQL = f'postgresql+psycopg2://{USERNAME}:{PASSWORD}@{HOSTNAME}/{DB}'
engine = sqlalchemy.create_engine(POSTGRESQL, echo=True)
            
con = engine.connect()
trans = con.begin()
LOAD_SQL = f"COPY tablename from '{OUTPUTFILE}' with csv delimiter E'\x01' quote E'\x02' null as '';"
try:
    con.execute(LOAD_SQL)
    trans.commit()
except Exception as e:
    trans.rollback()
finally:
    con.close()

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