When we discuss data modeling in terms of ServiceNow, we find that people remain focused on matters of reference fields, one-to-many links, and extensions on tables. All of this is very understandable and takes care of all our needs on a day-to-day basis. However, when we move on to performing larger implementations, especially in terms of applications for the enterprise level, we find that nothing is perfectly captured in the above model.
This is precisely where many-to-many relationships lie under the radar.
These concepts are seldom brought up, often overlooked, or even less often appreciated during the initial stages of familiarization with the ServiceNow system. However, without them, several of the most frequently used tools in the system would either fail or become a complete mess to handle.
This blog will take you through what many-to-many relationships are, why ServiceNow uses them so extensively, how they work beneath the surface, and when you should use many-to-many relationships in a real-world implementation scenario.
Why Simple Relationships Eventually Fall Short
At the beginning, one-to-many relationships seem to be enough.
- One user can create many incidents.
- One change can have several tasks.
Everything feels logical and controlled.
But then real business needs come.
- The user has to be part of several groups.
- A group must have several users.
- It is necessary for a configuration item to point to many services, and the services themselves need to point back to many CIs.
Trying to cram these situations into a one-to-many arrangement gives you grief right away. You either end up duplicating data, adding a lot of reference fields, or writing all kinds of custom scripts to keep things in sync. None of those approaches scales well. ServiceNow introduces M2M relationships to avoid this chaos.
What a Many-To-Many Relationship Really Means
A many-to-many relationship occurs when:
- A record in Table A may correspond to more than one record in Table B
- On the other side, a single record from Table B may be correlated with multiple relations from Table A
Neither “owns” a relationship.
Rather than being forced to put the relationship into one of these tables, ServiceNow inserts a third table, called a bridge table, or sometimes a junction table.
- There is no business information in this table.
- It only holds connections.
Every record in the many-to-many table corresponds to the association of two different records from different tables.
That’s it.
No repetition. No complex logic. Simple, clean, well-structured relationships.
An Example You Already Know Well
A case in point is Users and Groups.
- A user can be part of more than one group.
- A group may have multiple users.
Instead of maintaining multiple group fields on the users table or vice versa, ServiceNow has a many-to-many table connecting users and groups.
Every time you assign a user to the group, behind the scenes, the record is added to the M2M table for that object/record type.
You don’t see it.
You don’t manage it directly.
It just keeps everything humming along. The simplicity of the platform is because the complexities are hidden under.
Importance of Many-to-Many Tables Explained
Many-to-many relationships are valuable because they provide flexibility.
These enable ServiceNow to represent relationships in real life without having to assume boundaries or form.
Some important benefits are:
- No data duplication
- Data in tables is held in each table. Links to tables or other structures are held in a
- Clean Reporting
- Each relationship is a record in its own right, ensuring recordability accuracy
- Scalability
- Relationships may be added or dropped without modifying the base tables
- Improved performance over time
- Easy maintenance
Any change in one table doesn’t affect another table unpredictably. These benefits are clearer as applications increase.
Where Many-To-Many Relationships Exist in ServiceNow
Even if you haven’t ever made one by hand, you use M2M tables daily.
Typical examples include:
- Users ⇌ Groups
- Users <–> Roles
- Knowledge Articles <———-> Categories
- CIs ⇌ Services
- Incidents | – |Affected CIs
- Problems | Known Errors
All of these relationships are managed via a bridge table that ensures everything is well-organized without increasingly complicating the UI.
That is why ServiceNow feels intuitive and natural on the surface, but is working with complex logic.
How a Many-To-Many Table is Formatted
Usually, the many-to-many relationship table is refreshingly straightforward.
It typically includes:
- A reference field pointing to Table A
- A reference field referring to Table B
- Optional metadata (creation date, creation by, status, etc.)
That is all it needs.
Business Rules are not implemented in the table.
It does not store calculations.
It only stores relationships. This is by design. This ensures that the design remains malleable and dependable.
How ServiceNow simplifies the use of M2M tables
One reason many-to-many relationships don’t feel complicated is that ServiceNow hides the complexity behind the UI.
When you define a many-to-many relationship:
- Related lists can be auto-generated in ServiceNow.
- It can generate a UI action for adding related records.
- Users can manage the relations by using simple dialogs.
To the user, they are simply selecting values from a list.
In the background, ServiceNow inserts or deletes rows in an M2M table.
No scripting required.
When to Use a Many-to-Many Relationship
Many-to-many tables are the right choice when:
- Both tables must have several links to each other.
- The meaning is in the relationship itself.
- You need clean reporting on the relationship.
- You expect the data model to evolve.
They are particularly helpful in enterprise applications where the relations are bound to evolve.
When You Should Avoid Them
Despite their power, many-to-many relationships aren’t always the answer.
Avoid them when:
- A simple one-to-many relationship will suffice.
- There will never be more than one record on one side.
- The relationship does not add business value.
- You need extremely simple access logic.
The excessive use of M2M tables will make debugging more complex if the design does not warrant it.
A Real-World Example
To better understand this scenario, it would be helpful to consider an example.
- An instructor may teach various classes.
- A course can have multiple lecturers.
Storing this information in either of these tables confuses.
This is easily solved with a many-to-many table:
- It connects each record to exactly one instructor and exactly one course.
Optional entries include:
- Assignment date
- Status
- Teaching role
Now, reporting is made easy, the data remains clean, and it’s easy to handle changes in the future.
Why Business Owners Love M2M Relationships
From an admin standpoint, many-to-many tables:
- Reduce complexity in scripting
- Improve data integrity
- Clean up access modifiers
- Support the design for scalable applications
They allow admins to think in terms of relationships instead of workarounds.
That in and of itself saves countless amounts of time over the life of an application.
Final Thoughts
Many-to-many relationships in ServiceNow aren’t that exciting a feature. They don’t have dashboards or visual tools of any sort. You could go through a ServiceNow instance without ever noticing many-to-many relationships.
However, they also support some of the most crucial structures on the platform.
As soon as you begin applying these complex data models, you realize that they’re all around you. Once you realize how these complex data models work, it will not only improve the design but also make it more flexible and easier to maintain.
In some respects, many-to-many relationships are where ServiceNow is truly shining – where complexity is masked by simplicity and where the service is doing all of the heavy lifting for you.
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