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CreateRelationshipClass with MANY_TO_MANY - how?

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1
8 hours ago
nadja
by
Frequent Contributor
8 hours ago

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_tabledestination_tableout_relationship_classrelationship_typeforward_labelbackward_labelmessage_directioncardinalityattributedorigin_primary_keyorigin_foreign_keydestination_primary_keydestination_foreign_key
mgdm_polygone_polygonmgdm_polygone_regelpolygon_regelSIMPLERegelpolygonNONEMANY_TO_MANYNONERegelRegelRegelCode#
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1 Reply
TonyAlmeida
by MVP Regular Contributor
MVP Regular Contributor
an hour ago

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.")

 

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