XMLA Endpoint: Read-write operations require XMLA read/write enabled on the capacity
Context Manager: Always use with statement - changes are saved on exit
Service Principal: Supported via service_principal_authentication context
TOMWrapper Properties and Methods
Core Properties
with connect_semantic_model(dataset, workspace=workspace) as tom:
# Access the model
model = tom.model
# Get dataset info
dataset_id = tom._dataset_id
dataset_name = tom._dataset_name
workspace_id = tom._workspace_id
workspace_name = tom._workspace_name
# Check compatibility level
compat_level = tom._compat_level
Iterator Methods
Method
Returns
all_columns()
All columns in all tables
all_calculated_columns()
All calculated columns
all_calculated_tables()
All calculated tables
all_calculation_groups()
All calculation groups
all_measures()
All measures
all_partitions()
All partitions
all_hierarchies()
All hierarchies
all_levels()
All hierarchy levels
all_calculation_items()
All calculation items
all_functions()
All user-defined functions
Example: Iterating Objects
with connect_semantic_model(dataset, workspace=workspace) as tom:
# List all measuresfor measure in tom.all_measures():
print(f"Table: {measure.Parent.Name}, Measure: {measure.Name}")
# List all columnsfor column in tom.all_columns():
print(f"Table: {column.Table.Name}, Column: {column.Name}, Type: {column.DataType}")
# List all partitionsfor partition in tom.all_partitions():
print(f"Table: {partition.Table.Name}, Partition: {partition.Name}")
Reading Model Metadata
Tables
with connect_semantic_model(dataset, workspace=workspace) as tom:
for table in tom.model.Tables:
print(f"Table: {table.Name}")
print(f" Description: {table.Description}")
print(f" Is Hidden: {table.IsHidden}")
Columns
with connect_semantic_model(dataset, workspace=workspace) as tom:
for column in tom.all_columns():
print(f"Column: {column.Name}")
print(f" Table: {column.Table.Name}")
print(f" Data Type: {column.DataType}")
print(f" Is Hidden: {column.IsHidden}")
Measures
with connect_semantic_model(dataset, workspace=workspace) as tom:
for measure in tom.all_measures():
print(f"Measure: {measure.Name}")
print(f" Table: {measure.Parent.Name}")
print(f" Expression: {measure.Expression}")
print(f" Format String: {measure.FormatString}")
Relationships
with connect_semantic_model(dataset, workspace=workspace) as tom:
for rel in tom.model.Relationships:
print(f"From: {rel.FromTable.Name}[{rel.FromColumn.Name}]")
print(f"To: {rel.ToTable.Name}[{rel.ToColumn.Name}]")
print(f"Cross Filter: {rel.CrossFilteringBehavior}")
Modifying Model Metadata
Update Measure Properties
with connect_semantic_model(dataset, readonly=False, workspace=workspace) as tom:
measure = tom.model.Tables["Sales"].Measures["Revenue"]
measure.Description = "Total revenue"
measure.FormatString = "$#,##0.00"
measure.DisplayFolder = "Financial Metrics"
Update Column Properties
with connect_semantic_model(dataset, readonly=False, workspace=workspace) as tom:
column = tom.model.Tables["Date"].Columns["Month"]
column.IsHidden = False
column.Description = "Calendar month"
column.SortByColumn = tom.model.Tables["Date"].Columns["MonthNumber"]
Update Table Properties
with connect_semantic_model(dataset, readonly=False, workspace=workspace) as tom:
table = tom.model.Tables["Sales"]
table.Description = "Sales transactions"
table.IsHidden = False
Adding Model Objects
Add a Measure
import Microsoft.AnalysisServices.Tabular as TOM
with connect_semantic_model(dataset, readonly=False, workspace=workspace) as tom:
table = tom.model.Tables["Sales"]
new_measure = TOM.Measure()
new_measure.Name = "Total Sales"
new_measure.Expression = "SUM(Sales[Amount])"
new_measure.FormatString = "$#,##0.00"
new_measure.Description = "Sum of all sales amounts"
table.Measures.Add(new_measure)
Add a Calculated Column
import Microsoft.AnalysisServices.Tabular as TOM
with connect_semantic_model(dataset, readonly=False, workspace=workspace) as tom:
table = tom.model.Tables["Products"]
calc_column = TOM.Column()
calc_column.Name = "Profit Margin"
calc_column.Type = TOM.ColumnType.Calculated
calc_column.Expression = "[Revenue] - [Cost]"
calc_column.DataType = TOM.DataType.Decimal
table.Columns.Add(calc_column)
Add a Relationship
import Microsoft.AnalysisServices.Tabular as TOM
with connect_semantic_model(dataset, readonly=False, workspace=workspace) as tom:
from_column = tom.model.Tables["Sales"].Columns["ProductKey"]
to_column = tom.model.Tables["Products"].Columns["ProductKey"]
relationship = TOM.SingleColumnRelationship()
relationship.Name = f"{from_column.Table.Name}_{to_column.Table.Name}"
relationship.FromColumn = from_column
relationship.ToColumn = to_column
relationship.CrossFilteringBehavior = TOM.CrossFilteringBehavior.OneDirection
tom.model.Relationships.Add(relationship)
TOMWrapper Helper Methods
The TOMWrapper class includes many helper methods for common operations:
Display Methods (return DataFrames)
with connect_semantic_model(dataset, workspace=workspace) as tom:
# List all measures
df = tom.list_measures()
# List all columns
df = tom.list_columns()
# List all relationships
df = tom.list_relationships()
# List all partitions
df = tom.list_partitions()
with connect_semantic_model(dataset, readonly=False, workspace=workspace) as tom:
# Update measure expression
tom.update_measure(
table_name="Sales",
measure_name="Total Sales",
expression="SUMX(Sales, Sales[Quantity] * Sales[Price])"
)
Service Principal Authentication
from sempy_labs import service_principal_authentication
from sempy_labs.tom import connect_semantic_model
# Using Service Principalwith service_principal_authentication(
tenant_id="...",
client_id="...",
client_secret="..."
):
with connect_semantic_model(
dataset="My Model",
readonly=False,
workspace="My Workspace"
) as tom:
# Operations use Service Principal credentialsfor measure in tom.all_measures():
print(measure.Name)
Azure Analysis Services Support
The TOMWrapper also supports Azure Analysis Services:
with connect_semantic_model(
dataset="MyDatabase",
workspace="asazure://westus2.asazure.windows.net/myserver",
readonly=True
) as tom:
for table in tom.model.Tables:
print(table.Name)
Best Practices
Do's
✅ Always use context manager (with statement)
✅ Use readonly=True when only reading metadata
✅ Use iterator methods (all_measures(), etc.) for efficient traversal
✅ Save changes by exiting the context normally
Don'ts
❌ Don't open read-write connections when only reading
❌ Don't forget to handle exceptions (changes won't save on exception)
❌ Don't hold connections open longer than necessary
Error Handling
from sempy.fabric.exceptions import FabricHTTPException
try:
with connect_semantic_model(
dataset="My Model",
readonly=False,
workspace="My Workspace"
) as tom:
# Modifications...passexcept FabricHTTPException as e:
print(f"API error: {e}")
except Exception as e:
print(f"Error: {e}")
# Changes NOT saved due to exception