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# Data Access & Retrieval
This reference covers navigating OMERO's hierarchical data structure and retrieving objects.
## OMERO Data Hierarchy
### Standard Hierarchy
```
Project
└─ Dataset
└─ Image
```
### Screening Hierarchy
```
Screen
└─ Plate
└─ Well
└─ WellSample
└─ Image
```
## Listing Objects
### List Projects
```python
# List all projects for current user
for project in conn.listProjects():
print(f"Project: {project.getName()} (ID: {project.getId()})")
```
### List Projects with Filtering
```python
# Get current user and group
my_exp_id = conn.getUser().getId()
default_group_id = conn.getEventContext().groupId
# List projects with filters
for project in conn.getObjects("Project", opts={
'owner': my_exp_id, # Filter by owner
'group': default_group_id, # Filter by group
'order_by': 'lower(obj.name)', # Sort alphabetically
'limit': 10, # Limit results
'offset': 0 # Pagination offset
}):
print(f"Project: {project.getName()}")
```
### List Datasets
```python
# List all datasets
for dataset in conn.getObjects("Dataset"):
print(f"Dataset: {dataset.getName()} (ID: {dataset.getId()})")
# List orphaned datasets (not in any project)
for dataset in conn.getObjects("Dataset", opts={'orphaned': True}):
print(f"Orphaned Dataset: {dataset.getName()}")
```
### List Images
```python
# List all images
for image in conn.getObjects("Image"):
print(f"Image: {image.getName()} (ID: {image.getId()})")
# List images in specific dataset
dataset_id = 123
for image in conn.getObjects("Image", opts={'dataset': dataset_id}):
print(f"Image: {image.getName()}")
# List orphaned images
for image in conn.getObjects("Image", opts={'orphaned': True}):
print(f"Orphaned Image: {image.getName()}")
```
## Retrieving Objects by ID
### Get Single Object
```python
# Get project by ID
project = conn.getObject("Project", project_id)
if project:
print(f"Project: {project.getName()}")
else:
print("Project not found")
# Get dataset by ID
dataset = conn.getObject("Dataset", dataset_id)
# Get image by ID
image = conn.getObject("Image", image_id)
```
### Get Multiple Objects by ID
```python
# Get multiple projects at once
project_ids = [1, 2, 3, 4, 5]
projects = conn.getObjects("Project", project_ids)
for project in projects:
print(f"Project: {project.getName()}")
```
### Supported Object Types
The `getObject()` and `getObjects()` methods support:
- `"Project"`
- `"Dataset"`
- `"Image"`
- `"Screen"`
- `"Plate"`
- `"Well"`
- `"Roi"`
- `"Annotation"` (and specific types: `"TagAnnotation"`, `"FileAnnotation"`, etc.)
- `"Experimenter"`
- `"ExperimenterGroup"`
- `"Fileset"`
## Query by Attributes
### Query Objects by Name
```python
# Find images with specific name
images = conn.getObjects("Image", attributes={"name": "sample_001.tif"})
for image in images:
print(f"Found image: {image.getName()} (ID: {image.getId()})")
# Find datasets with specific name
datasets = conn.getObjects("Dataset", attributes={"name": "Control Group"})
```
### Query Annotations by Value
```python
# Find tags with specific text value
tags = conn.getObjects("TagAnnotation",
attributes={"textValue": "experiment_tag"})
for tag in tags:
print(f"Tag: {tag.getValue()}")
# Find map annotations
map_anns = conn.getObjects("MapAnnotation",
attributes={"ns": "custom.namespace"})
```
## Navigating Hierarchies
### Navigate Down (Parent to Children)
```python
# Project → Datasets → Images
project = conn.getObject("Project", project_id)
for dataset in project.listChildren():
print(f"Dataset: {dataset.getName()}")
for image in dataset.listChildren():
print(f" Image: {image.getName()}")
```
### Navigate Up (Child to Parent)
```python
# Image → Dataset → Project
image = conn.getObject("Image", image_id)
# Get parent dataset
dataset = image.getParent()
if dataset:
print(f"Dataset: {dataset.getName()}")
# Get parent project
project = dataset.getParent()
if project:
print(f"Project: {project.getName()}")
```
### Complete Hierarchy Traversal
```python
# Traverse complete project hierarchy
for project in conn.getObjects("Project", opts={'order_by': 'lower(obj.name)'}):
print(f"Project: {project.getName()} (ID: {project.getId()})")
for dataset in project.listChildren():
image_count = dataset.countChildren()
print(f" Dataset: {dataset.getName()} ({image_count} images)")
for image in dataset.listChildren():
print(f" Image: {image.getName()}")
print(f" Size: {image.getSizeX()} x {image.getSizeY()}")
print(f" Channels: {image.getSizeC()}")
```
## Screening Data Access
### List Screens and Plates
```python
# List all screens
for screen in conn.getObjects("Screen"):
print(f"Screen: {screen.getName()} (ID: {screen.getId()})")
# List plates in screen
for plate in screen.listChildren():
print(f" Plate: {plate.getName()} (ID: {plate.getId()})")
```
### Access Plate Wells
```python
# Get plate
plate = conn.getObject("Plate", plate_id)
# Plate metadata
print(f"Plate: {plate.getName()}")
print(f"Grid size: {plate.getGridSize()}") # e.g., (8, 12) for 96-well
print(f"Number of fields: {plate.getNumberOfFields()}")
# Iterate through wells
for well in plate.listChildren():
print(f"Well at row {well.row}, column {well.column}")
# Count images in well (fields)
field_count = well.countWellSample()
print(f" Number of fields: {field_count}")
# Access images in well
for index in range(field_count):
image = well.getImage(index)
print(f" Field {index}: {image.getName()}")
```
### Direct Well Access
```python
# Get specific well by row and column
well = plate.getWell(row=0, column=0) # Top-left well
# Get image from well
if well.countWellSample() > 0:
image = well.getImage(0) # First field
print(f"Image: {image.getName()}")
```
### Well Sample Access
```python
# Access well samples directly
for well in plate.listChildren():
for ws in well.listChildren(): # ws = WellSample
image = ws.getImage()
print(f"WellSample {ws.getId()}: {image.getName()}")
```
## Image Properties
### Basic Dimensions
```python
image = conn.getObject("Image", image_id)
# Pixel dimensions
print(f"X: {image.getSizeX()}")
print(f"Y: {image.getSizeY()}")
print(f"Z: {image.getSizeZ()} (Z-sections)")
print(f"C: {image.getSizeC()} (Channels)")
print(f"T: {image.getSizeT()} (Time points)")
# Image type
print(f"Type: {image.getPixelsType()}") # e.g., 'uint16', 'uint8'
```
### Physical Dimensions
```python
# Get pixel sizes with units (OMERO 5.1.0+)
size_x_obj = image.getPixelSizeX(units=True)
size_y_obj = image.getPixelSizeY(units=True)
size_z_obj = image.getPixelSizeZ(units=True)
print(f"Pixel Size X: {size_x_obj.getValue()} {size_x_obj.getSymbol()}")
print(f"Pixel Size Y: {size_y_obj.getValue()} {size_y_obj.getSymbol()}")
print(f"Pixel Size Z: {size_z_obj.getValue()} {size_z_obj.getSymbol()}")
# Get as floats (micrometers)
size_x = image.getPixelSizeX() # Returns float in µm
size_y = image.getPixelSizeY()
size_z = image.getPixelSizeZ()
```
### Channel Information
```python
# Iterate through channels
for channel in image.getChannels():
print(f"Channel {channel.getLabel()}:")
print(f" Color: {channel.getColor().getRGB()}")
print(f" Lookup Table: {channel.getLut()}")
print(f" Wavelength: {channel.getEmissionWave()}")
```
### Image Metadata
```python
# Acquisition date
acquired = image.getAcquisitionDate()
if acquired:
print(f"Acquired: {acquired}")
# Description
description = image.getDescription()
if description:
print(f"Description: {description}")
# Owner and group
details = image.getDetails()
print(f"Owner: {details.getOwner().getFullName()}")
print(f"Username: {details.getOwner().getOmeName()}")
print(f"Group: {details.getGroup().getName()}")
print(f"Created: {details.getCreationEvent().getTime()}")
```
## Object Ownership and Permissions
### Get Owner Information
```python
# Get object owner
obj = conn.getObject("Dataset", dataset_id)
owner = obj.getDetails().getOwner()
print(f"Owner ID: {owner.getId()}")
print(f"Username: {owner.getOmeName()}")
print(f"Full Name: {owner.getFullName()}")
print(f"Email: {owner.getEmail()}")
```
### Get Group Information
```python
# Get object's group
obj = conn.getObject("Image", image_id)
group = obj.getDetails().getGroup()
print(f"Group: {group.getName()} (ID: {group.getId()})")
```
### Filter by Owner
```python
# Get objects for specific user
user_id = 5
datasets = conn.getObjects("Dataset", opts={'owner': user_id})
for dataset in datasets:
print(f"Dataset: {dataset.getName()}")
```
## Advanced Queries
### Pagination
```python
# Paginate through large result sets
page_size = 50
offset = 0
while True:
images = list(conn.getObjects("Image", opts={
'limit': page_size,
'offset': offset,
'order_by': 'obj.id'
}))
if not images:
break
for image in images:
print(f"Image: {image.getName()}")
offset += page_size
```
### Sorting Results
```python
# Sort by name (case-insensitive)
projects = conn.getObjects("Project", opts={
'order_by': 'lower(obj.name)'
})
# Sort by ID (ascending)
datasets = conn.getObjects("Dataset", opts={
'order_by': 'obj.id'
})
# Sort by name (descending)
images = conn.getObjects("Image", opts={
'order_by': 'lower(obj.name) desc'
})
```
### Combining Filters
```python
# Complex query with multiple filters
my_exp_id = conn.getUser().getId()
default_group_id = conn.getEventContext().groupId
images = conn.getObjects("Image", opts={
'owner': my_exp_id,
'group': default_group_id,
'dataset': dataset_id,
'order_by': 'lower(obj.name)',
'limit': 100,
'offset': 0
})
```
## Counting Objects
### Count Children
```python
# Count images in dataset
dataset = conn.getObject("Dataset", dataset_id)
image_count = dataset.countChildren()
print(f"Dataset contains {image_count} images")
# Count datasets in project
project = conn.getObject("Project", project_id)
dataset_count = project.countChildren()
print(f"Project contains {dataset_count} datasets")
```
### Count Annotations
```python
# Count annotations on object
image = conn.getObject("Image", image_id)
annotation_count = image.countAnnotations()
print(f"Image has {annotation_count} annotations")
```
## Orphaned Objects
### Find Orphaned Datasets
```python
# Datasets not linked to any project
orphaned_datasets = conn.getObjects("Dataset", opts={'orphaned': True})
print("Orphaned Datasets:")
for dataset in orphaned_datasets:
print(f" {dataset.getName()} (ID: {dataset.getId()})")
print(f" Owner: {dataset.getDetails().getOwner().getOmeName()}")
print(f" Images: {dataset.countChildren()}")
```
### Find Orphaned Images
```python
# Images not in any dataset
orphaned_images = conn.getObjects("Image", opts={'orphaned': True})
print("Orphaned Images:")
for image in orphaned_images:
print(f" {image.getName()} (ID: {image.getId()})")
```
### Find Orphaned Plates
```python
# Plates not in any screen
orphaned_plates = conn.getObjects("Plate", opts={'orphaned': True})
for plate in orphaned_plates:
print(f"Orphaned Plate: {plate.getName()}")
```
## Complete Example
```python
from omero.gateway import BlitzGateway
# Connection details
HOST = 'omero.example.com'
PORT = 4064
USERNAME = 'user'
PASSWORD = 'pass'
# Connect and query data
with BlitzGateway(USERNAME, PASSWORD, host=HOST, port=PORT) as conn:
# Get user context
user = conn.getUser()
group = conn.getGroupFromContext()
print(f"Connected as {user.getName()} in group {group.getName()}")
print()
# List projects with datasets and images
for project in conn.getObjects("Project", opts={'limit': 5}):
print(f"Project: {project.getName()} (ID: {project.getId()})")
for dataset in project.listChildren():
image_count = dataset.countChildren()
print(f" Dataset: {dataset.getName()} ({image_count} images)")
# Show first 3 images
for idx, image in enumerate(dataset.listChildren()):
if idx >= 3:
print(f" ... and {image_count - 3} more")
break
print(f" Image: {image.getName()}")
print(f" Size: {image.getSizeX()}x{image.getSizeY()}")
print(f" Channels: {image.getSizeC()}, Z: {image.getSizeZ()}")
print()
```
## Best Practices
1. **Use Context Managers**: Always use `with` statements for automatic connection cleanup
2. **Limit Results**: Use `limit` and `offset` for large datasets
3. **Filter Early**: Apply filters to reduce data transfer
4. **Check for None**: Always check if `getObject()` returns None before using
5. **Efficient Traversal**: Use `listChildren()` instead of querying separately
6. **Count Before Loading**: Use `countChildren()` to decide whether to load data
7. **Group Context**: Set appropriate group context before cross-group queries
8. **Pagination**: Implement pagination for large result sets
9. **Object Reuse**: Cache frequently accessed objects to reduce queries
10. **Error Handling**: Wrap queries in try-except blocks for robustness