PowerBI Ambiguous Relationship Path Error

[DarylK_MA]

Hello Everyone,

I am building a bespoke reporting model that contains a cyclical relationship leading to possible ambiguous paths. My issue relates to how manipulating relationship cardinality can occasionally suppress or trigger ambiguous path errors.

In the screenshot below, it shows a data model that PowerBI accepts and commits as consistent without throwing any warnings and errors even though graphically there exists an ambiguous path - E.g. T4 can filter T7 either by the left path or right path of the circular relationship.

However, the relational keys between T6 and T7 are technically unique on each side and thus one-to-one. When I try to toggle T6-T7's relationship to one-to-one, I get thrown an error preventing the change from being commited. 

The ambiguous path of T4 filtering T7 exists regardless but an exception is only thrown when I try to define T6-T7's relationship as one-to-one and not when I define T6-T7's relationship as many-to-one.

I could be wrong (and do correct me if so) but my only guess is that this might have something to do with relationhip priority and weights which PowerBI resolves ambiguous relationships with (link here). However, I am not sure how these priority and weight rules are quantified and evaluated in the backend to trigger an error when T6-T7 is one-to-one but is silent when T6-T7 is many-to-one.

Appreciate if someone with a better understanding of this could offer some insights! Thank you! 😀

[v-priyankata]

Hi @DarylK_MA 

Thank you for reaching out to the Microsoft Fabric Forum Community.

@MohamedFowzan1 @burakkaragoz @sivarajan21 Thanks for the inputs.

I hope the information provided by users was helpful. If you still have questions, please don't hesitate to reach out to the community.

[sivarajan21]

Hi @DarylK_MA 

Practical options

• Leave T6-T7 as Many-to-One if you do not actually need 1-to-1 behaviour.

• If it is truly 1-to-1 and you need that semantic, break the cycle:

  • Make one of the other relationships inactive and use USERELATIONSHIP() in measures when you need it.

  • Introduce a bridge/dimension table to separate the loops.

  • Create a snowflake dimension structure to eliminate the cycle

• Keep cross-filter direction to Single wherever possible to reduce the chance of ambiguity.

Best Regards,

[burakkaragoz · Accepted solution]

Hi @DarylK_MA ,
The error appears only when you switch T6 ↔ T7 to 1:1 with Both-direction filtering because that change makes every leg in the ring fully symmetric. At *:1 the engine still gives one side (the 1 side) a higher internal priority so it quietly picks a single path. At 1:1 that priority disappears, so two active, equally valid routes exist between T4 and T7 and the model surfaces the ambiguity.

Core idea: a closed loop + multiple Both-direction relationships + peer (1:1) links = ambiguity.

Practical fixes (pick one):

1. Keep it Many to one and change some links to Single direction to break the loop.
2. Before switching to 1:1 set at least one other relationship in the ring to Single so only one full path remains.
3. Make one relationship inactive and use it only when needed:

Alt Path Measure =
CALCULATE ( [Base Measure], USERELATIONSHIP ( T6[One], T7[One] ) )

1. Merge T6 and T7 if they are always 1:1 and queried together.
2. Redesign toward a star schema (avoid circular bi-directional chains).

Optional sanity check for hidden duplicates:

T6 Duplicates = COUNTROWS(T6) - DISTINCTCOUNT(T6[One])

(Repeat for T7; expect 0.)

Key guidance: minimize bi-directional links, prefer a star layout, use inactive relationships or TREATAS when you only need an alternate path occasionally.

References:

• Create and manage relationships in Power BI Desktop
• USERELATIONSHIP function

Let me know which option you lean toward and I can outline the concrete steps.

If my response resolved your query, kindly mark it as the Accepted Solution to assist others. Additionally, I would be grateful for a 'Kudos' if you found my response helpful.
This response was assisted by AI for translation and formatting purposes.

[MohamedFowzan1]

Hi @DarylK_MA 

Baically using one to one gives the same priority on either sides, its better to have them as 1 to many, if absolutely necessary it would be better to have a inactive join and use functions like RELATED or USERELATIONSHIP where necessary.

Main Pointers

- Power BI uses priority and weight rules to resolve which path to use for filtering when multiple paths (cycles) exist between two tables.

- With many-to-one, Power BI can assign different priorities to the two filter paths, allowing it to choose between them and thus not flag the ambiguity.

- With one-to-one on T6–T7, both paths between T4 and T7 are now of the same priority and weight, so Power BI can’t resolve ambiguity, triggering the error.

- Avoid 1:1 active relationships in cyclical layouts, especially if all paths are bidirectional. Prefer 1:n with single-direction or a combination of inactive relationships.

- If you must keep the relationship, use one of them as inactive, and activate it contextually with USERELATIONSHIP in DAX.

Reference: https://learn.microsoft.com/en-us/power-bi/transform-model/desktop-relationships-understand