Use the Command-Line Interface¶

Start an interactive Python REPL with DataJoint pre-loaded.

The dj command provides quick access to DataJoint for exploring schemas, running queries, and testing connections without writing scripts.

Start the REPL¶

dj

This opens a Python REPL with dj (DataJoint) already imported:

DataJoint 2.0.0 REPL
Type 'dj.' and press Tab for available functions.

>>> dj.conn()  # Connect to database
>>> dj.list_schemas()  # List available schemas

Specify Database Credentials¶

Override config file settings from the command line:

dj --host localhost:3306 --user root --password secret

Option	Description
`--host HOST`	Database host as `host:port`
`-u`, `--user USER`	Database username
`-p`, `--password PASS`	Database password

Credentials from command-line arguments override values in config files.

Load Schemas as Virtual Modules¶

Load database schemas directly into the REPL namespace:

dj -s my_lab:lab -s my_analysis:analysis

The format is schema_name:alias where:

schema_name is the database schema name
alias is the variable name in the REPL

This outputs:

DataJoint 2.0.0 REPL
Type 'dj.' and press Tab for available functions.

Loaded schemas:
  lab -> my_lab
  analysis -> my_analysis

>>> lab.Subject.to_dicts()  # Query Subject table
>>> dj.Diagram(lab.schema)  # View schema diagram

Common Workflows¶

Explore an Existing Schema¶

dj -s production_db:db

>>> list(db.schema)  # List all tables
>>> db.Experiment().to_dicts()[:5]  # Preview data
>>> dj.Diagram(db.schema)  # Visualize structure

Quick Data Check¶

dj --host db.example.com -s my_lab:lab

>>> len(lab.Session())  # Count sessions
>>> lab.Session.describe()  # Show table definition

Test Connection¶

dj --host localhost:3306 --user testuser --password testpass

>>> dj.conn()  # Verify connection works
>>> dj.list_schemas()  # Check accessible schemas

Version Information¶

Display DataJoint version:

dj --version

Help¶

Display all options:

dj --help

Entry Points¶

The CLI is available as both dj and datajoint:

dj --version
datajoint --version  # Same command

Programmatic Usage¶

The CLI function can also be called from Python:

from datajoint.cli import cli

# Show version and exit
cli(["--version"])

# Start REPL with schemas
cli(["-s", "my_lab:lab"])