Connection & Session Management

Connection & Session Management

This reference covers establishing and managing connections to OMERO servers using BlitzGateway.

Basic Connection

Standard Connection Pattern

from omero.gateway import BlitzGateway

# Create connection
conn = BlitzGateway(username, password, host=host, port=4064)

# Connect to server
if conn.connect():
    print("Connected successfully")
    # Perform operations
    conn.close()
else:
    print("Failed to connect")

Connection Parameters

• username (str): OMERO user account name
• password (str): User password
• host (str): OMERO server hostname or IP address
• port (int): Server port (default: 4064)
• secure (bool): Force encrypted connection (default: False)

Secure Connection

To ensure all data transfers are encrypted:

conn = BlitzGateway(username, password, host=host, port=4064, secure=True)
conn.connect()

Context Manager Pattern (Recommended)

Use context managers for automatic connection management and cleanup:

from omero.gateway import BlitzGateway

with BlitzGateway(username, password, host=host, port=4064) as conn:
    # Connection automatically established
    for project in conn.getObjects('Project'):
        print(project.getName())
    # Connection automatically closed on exit

Benefits:

• Automatic connect() call
• Automatic close() call on exit
• Exception-safe resource cleanup
• Cleaner code

Session Management

Connection from Existing Client

Create BlitzGateway from an existing omero.client session:

import omero.clients
from omero.gateway import BlitzGateway

# Create client and session
client = omero.client(host, port)
session = client.createSession(username, password)

# Create BlitzGateway from existing client
conn = BlitzGateway(client_obj=client)

# Use connection
# ...

# Close when done
conn.close()

Retrieve Session Information

# Get current user information
user = conn.getUser()
print(f"User ID: {user.getId()}")
print(f"Username: {user.getName()}")
print(f"Full Name: {user.getFullName()}")
print(f"Is Admin: {conn.isAdmin()}")

# Get current group
group = conn.getGroupFromContext()
print(f"Current Group: {group.getName()}")
print(f"Group ID: {group.getId()}")

Check Admin Privileges

if conn.isAdmin():
    print("User has admin privileges")

if conn.isFullAdmin():
    print("User is full administrator")
else:
    # Check specific admin privileges
    privileges = conn.getCurrentAdminPrivileges()
    print(f"Admin privileges: {privileges}")

Group Context Management

OMERO uses groups to manage data access permissions. Users can belong to multiple groups.

Get Current Group Context

# Get the current group context
group = conn.getGroupFromContext()
print(f"Current group: {group.getName()}")
print(f"Group ID: {group.getId()}")

Query Across All Groups

Use group ID -1 to query across all accessible groups:

# Set context to query all groups
conn.SERVICE_OPTS.setOmeroGroup('-1')

# Now queries span all accessible groups
image = conn.getObject("Image", image_id)
projects = conn.listProjects()

Switch to Specific Group

Switch context to work within a specific group:

# Get group ID from an object
image = conn.getObject("Image", image_id)
group_id = image.getDetails().getGroup().getId()

# Switch to that group's context
conn.SERVICE_OPTS.setOmeroGroup(group_id)

# Subsequent operations use this group context
projects = conn.listProjects()

List Available Groups

# Get all groups for current user
for group in conn.getGroupsMemberOf():
    print(f"Group: {group.getName()} (ID: {group.getId()})")

Advanced Connection Features

Substitute User Connection (Admin Only)

Administrators can create connections acting as other users:

# Connect as admin
admin_conn = BlitzGateway(admin_user, admin_pass, host=host, port=4064)
admin_conn.connect()

# Get target user
target_user = admin_conn.getObject("Experimenter", user_id).getName()

# Create connection as that user
user_conn = admin_conn.suConn(target_user)

# Operations performed as target user
for project in user_conn.listProjects():
    print(project.getName())

# Close substitute connection
user_conn.close()
admin_conn.close()

List Administrators

# Get all administrators
for admin in conn.getAdministrators():
    print(f"ID: {admin.getId()}, Name: {admin.getFullName()}, "
          f"Username: {admin.getOmeName()}")

Connection Lifecycle

Closing Connections

Always close connections to free server resources:

try:
    conn = BlitzGateway(username, password, host=host, port=4064)
    conn.connect()

    # Perform operations

except Exception as e:
    print(f"Error: {e}")
finally:
    if conn:
        conn.close()

Check Connection Status

if conn.isConnected():
    print("Connection is active")
else:
    print("Connection is closed")

Error Handling

Robust Connection Pattern

from omero.gateway import BlitzGateway
import traceback

def connect_to_omero(username, password, host, port=4064):
    """
    Establish connection to OMERO server with error handling.

    Returns:
        BlitzGateway connection object or None if failed
    """
    try:
        conn = BlitzGateway(username, password, host=host, port=port, secure=True)
        if conn.connect():
            print(f"Connected to {host}:{port} as {username}")
            return conn
        else:
            print("Failed to establish connection")
            return None
    except Exception as e:
        print(f"Connection error: {e}")
        traceback.print_exc()
        return None

# Usage
conn = connect_to_omero(username, password, host)
if conn:
    try:
        # Perform operations
        pass
    finally:
        conn.close()

Common Connection Patterns

Pattern 1: Simple Script

from omero.gateway import BlitzGateway

# Connection parameters
HOST = 'omero.example.com'
PORT = 4064
USERNAME = 'user'
PASSWORD = 'pass'

# Connect
with BlitzGateway(USERNAME, PASSWORD, host=HOST, port=PORT) as conn:
    print(f"Connected as {conn.getUser().getName()}")
    # Perform operations

Pattern 2: Configuration-Based Connection

import yaml
from omero.gateway import BlitzGateway

# Load configuration
with open('omero_config.yaml', 'r') as f:
    config = yaml.safe_load(f)

# Connect using config
with BlitzGateway(
    config['username'],
    config['password'],
    host=config['host'],
    port=config.get('port', 4064),
    secure=config.get('secure', True)
) as conn:
    # Perform operations
    pass

Pattern 3: Environment Variables

import os
from omero.gateway import BlitzGateway

# Get credentials from environment
USERNAME = os.environ.get('OMERO_USER')
PASSWORD = os.environ.get('OMERO_PASSWORD')
HOST = os.environ.get('OMERO_HOST', 'localhost')
PORT = int(os.environ.get('OMERO_PORT', 4064))

# Connect
with BlitzGateway(USERNAME, PASSWORD, host=HOST, port=PORT) as conn:
    # Perform operations
    pass

Best Practices

1. Use Context Managers: Always prefer context managers for automatic cleanup
2. Secure Connections: Use secure=True for production environments
3. Error Handling: Wrap connection code in try-except blocks
4. Close Connections: Always close connections when done
5. Group Context: Set appropriate group context before queries
6. Credential Security: Never hardcode credentials; use environment variables or config files
7. Connection Pooling: For web applications, implement connection pooling
8. Timeouts: Consider implementing connection timeouts for long-running operations

Troubleshooting

Connection Refused

Unable to contact ORB

Solutions:

• Verify host and port are correct
• Check firewall settings
• Ensure OMERO server is running
• Verify network connectivity

Authentication Failed

Cannot connect to server

Solutions:

• Verify username and password
• Check user account is active
• Verify group membership
• Check server logs for details

Session Timeout

Solutions:

• Increase session timeout on server
• Implement session keepalive
• Reconnect on timeout
• Use connection pools for long-running applications