Cassandra query by a field in JSON - json

Question

I'm using the latest cassandra version and trying to save JSON like below and was successful,
INSERT INTO mytable JSON '{"username": "myname", "country": "mycountry", "userid": "1"}'
Above query saves the record like,
"rows": [
{
"[json]": "{\"userid\": \"1\", \"country\": \"india\", \"username\": \"sai\"}"
}
],
"rowLength": 1,
"columns": [
{
"name": "[json]",
"type": {
"code": 13,
"type": null
}
}
]
Now I would like to retrieve the record based on userid:
SELECT JSON * FROM mytable WHERE userid = fromJson("1") // but this query throws error
All this occurs in a node/express app and I'm using dse-driver as the client driver.

Answer 1

The CQL command worked like below,
SELECT JSON * FROM mytable WHERE userid="1";
However if it has to be executed via the dse-driver then the below snippet worked,
let query = 'SELECT JSON * FROM mytable WHERE userid = ?';
client.execute(query, ["1"], { prepare: true });
where client is,
const dse = require('dse-driver');
const client = new dse.Client({
contactPoints: ['h1', 'h2'],
authProvider: new dse.auth.DsePlainTextAuthProvider('username', 'pass')
});

Answer 2

If your Cassandra version is 2.1x and below, you can use the Python-based approach. Write a python script using Cassandra-Python API
Here you have to get your row first and then use python json's loads method, which will convert your json text column value into JSON object which will be dict in Python. Then you can play around with Python dictionaries and extract your required nested keys. See the below code snippet.
from cassandra.cluster import Cluster
from cassandra.auth import PlainTextAuthProvider
import json
if __name__ == '__main__':
auth_provider = PlainTextAuthProvider(username='xxxx', password='xxxx')
cluster = Cluster(['0.0.0.0'],
port=9042, auth_provider=auth_provider)
session = cluster.connect("keyspace_name")
print("session created successfully")
rows = session.execute('select * from user limit 10')
for user_row in rows:
#fetchign your json column
column_dict = json.loads(user_row.json_col)
print(column_dict().keys()

Answer 3

Assuming user-id is the partition key, and assuming you want to retrieve a JSON object corresponding to user of id 1, you should try:
SELECT JSON * FROM mytable WHERE userid=1;
If userid is of type text, you will need to add some quotes.