Create Relationship Class (Data Management)

Summary

This tool creates a relationship class to store an association between fields or features in the origin table and the destination table.

Usage

• Relationships can exist between spatial objects (features in feature classes), nonspatial objects (rows in a table), or spatial and nonspatial objects.

• Once created, a relationship class cannot be modified; you can only add, delete, or refine its rules. Relationship classes can be deleted and renamed using ArcCatalog in the same manner as any other object in the database.

• For many-to-many relationship classes, a new table is created in the database to store the foreign keys used to link the origin and destination classes. This table can also have other fields to store attributes of the relationship itself that are not attributed to either the origin or destination class. For example, in a parcel database, you might have a relationship class between parcels and owners in which owners "own" parcels and parcels are "owned by" owners. An attribute of that relationship could be percentage ownership. One-to-one and one-to-many relationship classes can also have attributes; in this case, a table is created to store the relationships.

• Simple or peer-to-peer relationships involve two or more objects in the database that exist independently of each other. For example, in a railroad network, you might have railroad crossings that have one or more related signal lamps. However, a railroad crossing can exist without a signal lamp, and signal lamps exist on the railroad network where there are no railroad crossings. Simple relationships can have one-to-one, one-to-many, or many-to-many cardinality.

• A composite relationship is one in which the lifetime of one object controls the lifetime of its related objects. For example, power poles support transformers, and transformers are mounted on poles. Once a pole is deleted, a delete message is propagated to its related transformers, which are deleted from the transformers' feature class. Composite relationships are always one-to-many.

• Forward and backward path labels describe the relationship when navigating from one object to another. The forward path label describes the relationship navigated from the origin class to the destination class. In the pole-transformer example, a forward path label might be "Poles support transformers." The backward path label describes the relationship navigated from the destination to the origin class. In the pole-transformer example, a backward path label might be"Transformers are mounted on poles."

• Relationship classes can also be created in ArcCatalog. Select the command New > Relationship Class from the context menu of a geodatabase.

Syntax

CreateRelationshipClass_management (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})

Parameter	Explanation	Data Type
origin_table	The table or feature class that is associated to the destination table.	Table View
destination_table	The table that is associated to the origin table.	Table View
out_relationship_class	The relationship class that is created.	Relationship Class
relationship_type	The type of relationship to create between the origin and destination tables. SIMPLE —A relationship between independent objects (parent to parent). This is the default. COMPOSITE —A relationship between dependent objects where the lifetime of one object controls the lifetime of the related object (parent to child).	String
forward_label	A name to uniquely identify the relationship when navigating from the origin table to the destination table.	String
backward_label	A name to uniquely identify the relationship when navigating from the destination table to the origin table.	String
message_direction	The direction in which messages are passed between the origin and destination tables. For example, in a relationship between poles and transformers, when the pole is deleted, it sends a message to its related transformer objects informing them it was deleted. FORWARD —Messages are passed from the origin to the destination table. BACK —Messages are passed from the destination to the origin table. BOTH —Messages are passed from the origin to the destination table and from the destination to the origin table. NONE —No messages passed. This is the default.	String
cardinality	Determines how many relationships exist between rows or features in the origin and rows or features in the destination table. ONE_TO_ONE —Each row or feature in the origin table can be related to zero or one row or feature in the destination table. This is the default. ONE_TO_MANY —Each row or feature in the origin table can be related to one or several rows or features in the destination table. MANY_TO_MANY —Several fields or features in the origin table can be related to one or several rows or features in the destination table.	String
attributed	Specifies if the relationship will have attributes. NONE —Indicates the relationship class will not have attributes. This is the default. ATTRIBUTED —Indicates the relationship class will have attributes.	Boolean
origin_primary_key	The field in the origin table, typically the OID field, that links it to the Origin Foreign Key field in the relationship class table.	String
origin_foreign_key	The field in the relationship class table that links it to the Origin Primary Key field in the origin table.	String
destination_primary_key (Optional)	The field in the destination table, typically the OID field, that links it to the Destination Foreign Key field in the relationship class table.	String
destination_foreign_key (Optional)	The field in the relationship class table that links it to the Destination Primary Key field in the destination table.	String

Code Sample

Create Relationship Class example (Python window)

The following Python Window script demonstrates how to use the Create Relationship Class tool.

import arcpy
arcpy.env.workspace = "C:/data/Habitat_Analysis.gdb"
arcpy.CreateRelationshipClass_management("vegtype", "vegtable", "veg_RelClass", "SIMPLE", "Attributes from vegtable", "Attributes and Features from vegtype", "NONE", "ONE_TO_ONE", "NONE", "HOLLAND95", "HOLLAND95")

Create Relationship Class example 1 (Stand-alone script)

Create a relationship class between vegetation feature class and table with additional vegetation information.

# Name: CreateRelationshipClass.py
# Description: Create a relationship class between vegetation feature
#                    class and table with additional vegetation information
# Author: ESRI

# import system modules 
import arcpy
from arcpy import env

# Set environment settings
env.workspace = "C:/data"

# Copy vegtable.dbf to file gdb table, since both tables to be related
#  must be in the same database
vegDbf = "vegtable.dbf"
vegTbl = "Habitat_Analysis.gdb/vegtable"
arcpy.CopyRows_management(vegDbf, vegTbl)

# Create simple relationship class between 'vegtype' vegetation layer
#  and 'vegtable' table with additional vegetation information
veg = "Habitat_Analysis.gdb/vegtype"
relClass = "Habitat_Analysis.gdb/veg_RelClass"
forLabel = "Attributes from vegtable"
backLabel = "Attributes and Features from vegtype"
primaryKey = "HOLLAND95"
foreignKey = "HOLLAND95"
arcpy.CreateRelationshipClass_management(veg, vegTbl, relClass, "SIMPLE", forLabel, 
					      backLabel, "NONE", "ONE_TO_ONE", 
					     "NONE", primaryKey, foreignKey)

Create Relationship Class example 2 (Stand-alone script)

Create a relationship class between parcel feature class and a table with owner information.

# Name: CreateRelationshipClass.py
# Description: Create a relationship class between parcels feature
#                    class and table with owner information
# Author: ESRI

# import system modules 
import arcpy
from arcpy import env

# Set environment settings
env.workspace = "C:/data"

# Copy owners.dat to file gdb table, since both tables to be related
#  must be in the same database
ownerDat = "owners.dat"
ownerTbl = "Montgomery.gdb/owners"
arcpy.CopyRows_management(ownerDat, ownerTbl)

# Create simple relationship class between 'parcel' parcel layer
#  and 'owner' table with additional parcel owner information
parcel = "Montgomery.gdb/Parcels"
relClass = "Montgomery.gdb/parcelowners_RelClass"
forLabel = "Owns"
backLabel = "Is Owned By"
primaryKey = "PROPERTY_ID"
foreignKey = "PROPERTY_I"
arcpy.CreateRelationshipClass_management(ownerTbl, parcel, relClass, "SIMPLE", forLabel, 
					     backLabel, "BACKWARD", "ONE_TO_MANY", 
					     "NONE", primaryKey, foreignKey)

Environments

Auto Commit, Current Workspace

Licensing Information

ArcGIS for Desktop Basic: No

ArcGIS for Desktop Standard: Yes

ArcGIS for Desktop Advanced: Yes