topic Re: CreateRelationshipClass with MANY_TO_MANY - how? in Python Questions

CreateRelationshipClass with MANY_TO_MANY - how?

nadja — Mon, 17 Nov 2025 08:44:58 GMT

I'm trying to create several Relationship Classes with the cardinalities 1:1 and n:n. The below script works fine with my 1:1 relationship classes. It runs also for the n:n cardinalities, creates some relationship classes, but I can't access its values with the explore tool as with the 1:1 relationship classes. Why? What's wrong?

for index, row in df.iterrows(): arcpy.management.CreateRelationshipClass(origin_table = row["origin_table"], destination_table = row["destination_table"], out_relationship_class = row["out_relationship_class"], relationship_type = row["relationship_type"], forward_label = row["forward_label"], backward_label = row["backward_label"], message_direction = row["message_direction"], cardinality = row["cardinality"], attributed = row["attributed"], origin_primary_key = row["origin_primary_key"], origin_foreign_key = row["origin_foreign_key"], destination_primary_key = row["destination_primary_key"], destination_foreign_key = row["destination_foreign_key"])

with my table:

origin_table

destination_table

out_relationship_class

relationship_type

forward_label

backward_label

message_direction

cardinality

attributed

origin_primary_key

origin_foreign_key

destination_primary_key

destination_foreign_key

mgdm_polygone_polygon

mgdm_polygone_regel

polygon_regel

SIMPLE

Regel

polygon

NONE

MANY_TO_MANY

NONE

Regel

RegelCode

Re: CreateRelationshipClass with MANY_TO_MANY - how?

TonyAlmeida — Mon, 17 Nov 2025 15:44:17 GMT

ArcGIS creates intermediate relationship table that stores the pairs of related objects. Unlike 1:1 relationships, you cannot directly access related records through the Explore tool without this intermediate table.

Try something like this.

import arcpy import os def create_relationship_with_intermediate_check(row): """Create relationship class and handle intermediate table for n:n""" # Create the relationship class arcpy.management.CreateRelationshipClass( origin_table=row["origin_table"], destination_table=row["destination_table"], out_relationship_class=row["out_relationship_class"], relationship_type=row["relationship_type"], forward_label=row["forward_label"], backward_label=row["backward_label"], message_direction=row["message_direction"], cardinality=row["cardinality"], attributed=row["attributed"], origin_primary_key=row["origin_primary_key"], origin_foreign_key=row["origin_foreign_key"], destination_primary_key=row["destination_primary_key"], destination_foreign_key=row["destination_foreign_key"] ) # Handle n:n specific setup if row["cardinality"].upper() == "MANY_TO_MANY": handle_many_to_many_relationship(row) def handle_many_to_many_relationship(row): """Locate and verify the intermediate table for an n:n relationship class.""" relationship_class = row["out_relationship_class"] print(f"n:n Relationship created: {relationship_class}") # Describe the relationship class desc = arcpy.Describe(relationship_class) # ArcGIS tells us exactly which table is the join table rel_table_path = desc.relationshipTable if not rel_table_path: print("No intermediate relationship table found (Describe returned None).") return print(f"Intermediate table located: {rel_table_path}") # Verify it exists if arcpy.Exists(rel_table_path): print("Intermediate relationship table verified") # Inspect fields rel_desc = arcpy.Describe(rel_table_path) fields = [f.name for f in rel_desc.fields] print(f"Relationship table fields: {fields}") else: print("Relationship table path does not exist in the workspace.")

Re: CreateRelationshipClass with MANY_TO_MANY - how?

nadja — Tue, 18 Nov 2025 06:52:36 GMT

Thank you @TonyAlmeida. If I understand your code correctly, this assumes that there already is an intermediate relationship table, correct? how do you create such a table? I found https://pro.arcgis.com/en/pro-app/3.4/tool-reference/data-management/table-to-relationship-class.htm, but this gp tool too assumes there is already such an intermediate table.

Re: CreateRelationshipClass with MANY_TO_MANY - how?

nadja — Tue, 18 Nov 2025 10:34:47 GMT

I get an error if i try to access the relationshipTable from a RelationshipClass using

print(rc.relationshipTable)

AttributeError: DescribeData: Method relationshipTable does not exist

Re: CreateRelationshipClass with MANY_TO_MANY - how?

TonyAlmeida — Tue, 18 Nov 2025 15:28:25 GMT

Yes, the code assumes the intermediate table already exists.
But ArcGIS automatically creates the intermediate table for you when BOTH of the following are true:

cardinality = "MANY_TO_MANY"

attributed = "NONE" (i.e., NOT attributed)

Re: CreateRelationshipClass with MANY_TO_MANY - how?

TonyAlmeida — Tue, 18 Nov 2025 15:35:19 GMT

Try this,

Set the parameter values to:

cardinality = "MANY_TO_MANY"
attributed = "NONE"

and

row dictionary contains:
row["cardinality"] = "MANY_TO_MANY"
row["attributed"] = "NONE"

import arcpy import os def create_relationship_with_intermediate_check(row): """Create relationship class and handle intermediate table for n:n""" # Should auto-create the join table if row["cardinality"].upper() == "MANY_TO_MANY": row["attributed"] = "NONE" # REQUIRED for system-generated table # Create the relationship class arcpy.management.CreateRelationshipClass( origin_table=row["origin_table"], destination_table=row["destination_table"], out_relationship_class=row["out_relationship_class"], relationship_type=row["relationship_type"], forward_label=row["forward_label"], backward_label=row["backward_label"], message_direction=row["message_direction"], cardinality=row["cardinality"], attributed=row["attributed"], origin_primary_key=row["origin_primary_key"], origin_foreign_key=row["origin_foreign_key"], destination_primary_key=row["destination_primary_key"], destination_foreign_key=row["destination_foreign_key"] ) # Handle M:N after creation if row["cardinality"].upper() == "MANY_TO_MANY": handle_many_to_many_relationship(row) def handle_many_to_many_relationship(row): """Locate and verify the intermediate table for an n:n (non-attributed) relationship.""" relationship_class = row["out_relationship_class"] print(f"n:n Relationship created: {relationship_class}") desc = arcpy.Describe(relationship_class) # SAFE ATTRIBUTE CHECK if hasattr(desc, "relationshipTable"): rel_table_path = desc.relationshipTable else: print("No system-generated intermediate table exists (attributed=ATTRIBUTED or invalid RC).") return if not rel_table_path: print("Describe returned a blank relationshipTable property.") return print(f"Intermediate table located: {rel_table_path}") if arcpy.Exists(rel_table_path): print("Intermediate table verified.") # List fields fields = [f.name for f in arcpy.ListFields(rel_table_path)] print(f"Relationship table fields: {fields}") else: print("Relationship table does not exist in the workspace.")