Kha Cloud Documentation

# Transferring Tables From One MongoDB Database to Another

The process outlined in the server logs can be divided into a few major steps:

  1. Backup of collections from the source database.
  2. Modification of the backup files if necessary.
  3. Restoration of the backup into the target database.

# 1. Back Up the Collection From the Source Database

Use mongodump to back up the collection:

mongodump -u admin -p "<password>" --authenticationDatabase=admin --db <source_db> --collection <collection_name> --out /tmp/path/to/backup-folder

Replace <password>, <source_db>, <collection_name>, and /tmp/path/to/backup-folder with your MongoDB credentials, the name of the source database, the name of the collection you want to transfer, and the output path for the backup files, respectively.

# 2. (Optional) Modify the Backup Files

If necessary, you may want to modify the backup files. This may involve changing some database-specific strings in the backup file. Use sed to perform the modifications:

  • Install python3-pip and pymongo if you haven't already:
apt install python3-pip
pip install pymongo
  • Create the replacement script collection_replacer.py:
nano collection_replacer.py

import argparse
import bson

def replace_nested(obj, old_text, new_text):
    if isinstance(obj, str):
        return obj.replace(old_text, new_text)
    elif isinstance(obj, dict):
        return {k: replace_nested(v, old_text, new_text) for k, v in obj.items()}
    elif isinstance(obj, list):
        return [replace_nested(elem, old_text, new_text) for elem in obj]
    else:
        return obj

def main(bson_filepath, old_text, new_text):
    # Read BSON file and decode to a Python dict
    with open(bson_filepath, 'rb') as f:
        bson_data = f.read()
    data = bson.decode_all(bson_data)

    # Perform string replacement
    data = [replace_nested(d, old_text, new_text) for d in data]

    # Encode dict back to BSON and write to file
    with open(bson_filepath, 'wb') as f:
        for d in data:
            f.write(bson.BSON.encode(d))

if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="Replace text in BSON file")
    parser.add_argument("bson_filepath", help="Path to BSON file")
    parser.add_argument("old_text", help="Text to replace")
    parser.add_argument("new_text", help="Text to replace with")
    args = parser.parse_args()

    main(args.bson_filepath, args.old_
    text, args.new_text)

python3 collection_replacer.py /tmp/new_ehs/settings.bson ehs/uploads ehs_migrated/uploads

Please note that binary files such as .bson files aren't meant to be manipulated using text processing tools like sed. This operation could potentially corrupt the file.

# 3. Restore the Backup Into the Target Database

Use mongorestore to restore the backup into the target database:

mongorestore -u admin -p "<password>" --authenticationDatabase=admin --db <target_db> --collection <collection_name> --drop /tmp/path/to/backup-folder/<collection_name>.bson

Replace <password>, <target_db>, <collection_name>, and /tmp/path/to/backup-folder with your MongoDB credentials, the name of the target database, the name of the collection, and the path to the backup files, respectively.

--drop is an optional flag that tells MongoDB to drop the collection from the target database if it exists before performing the restore operation.

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