Error: Duplicate object key: "Two different items produced the key" in a for expression

Not specified by the original author.

TL;DR

Your { for ... : key [your value] value } produced the same key twice. Terraform refuses to guess which value wins. Either make the keys unique, or add the grouping ellipsis (...) after the value expression to collect duplicates into lists.

The error

Error: Duplicate object key

  on .terraform/modules/repository/main.tf line 404, in locals:
 398:   teams = { for i in concat(
 399:     local.team_admin,
 400:     local.team_push,
 401:     local.team_pull,
 402:     local.team_triage,
 403:     local.team_maintain,
 404:   ) : i.slug => i }

Two different items produced the key "nios-build-write" in this 'for' expression.

Steps to fix

1. Read which key collided (here: nios-build-write). Find the two items that produce it.

   • Expected: you can point at both source items.

2. Decide: should duplicates merge or group? If one should win, restructure so keys are unique (e.g. merge() several single-key maps, later arguments winning), or key by a composite like "${i.slug}-${i.permission}". If duplicates are legitimate, enable grouping:

   teams = { for i in local.all_teams : i.slug => i... }

   • Expected: each key maps to a list of values; downstream code indexes into lists.

3. Run terraform validate, then plan and check the resulting map.

   • Expected: no duplicate-key error; the map shape matches what consumers expect.

When to use this

• plan/validate fails with Duplicate object key in a for expression building a map, usually after concatenating lists that can share keys.

When NOT to use this

• Duplicate resource configuration is about resource blocks, not map keys. If the collision is unexpected, grouping with ... hides a data bug; prefer making keys unique.

Compatibility

• Terraform 0.12+ for expressions; the grouping ellipsis is available in all 1.x versions.

Root cause

Object construction requires unique keys. When two iterations emit the same key, Terraform cannot pick a value without silently dropping data, so it errors. The ... ellipsis opts into the explicit alternative: group values per key into a list.

Edge cases

• for_each over the resulting map with grouped values gives you lists per key; adjust each.value handling.
• The ellipsis only works when building objects, not tuples: [for ... : k...] errors.
• distinct() on the input list before the for expression is another way to force uniqueness when duplicates are noise.

mineiros-io/terraform-github-repository#180 is a real instance: terraform plan fails building the teams local with "Error: Duplicate object key ... Two different items produced the key \"nios-build-write\" in this 'for' expression." The cause was the same team slug appearing in more than one permission list (teamadmin, teampush, teampull, teamtriage, team_maintain) while the concat + for pattern does not tolerate duplicate keys. The proposed fix replaces it with merge() of individual maps ordered by ascending privilege so the highest permission wins. The error message itself suggests the ellipsis (...) grouping alternative.

Not specified by the original author.

TL;DR

Query the source grouped by the key to find the duplicated keys, fix the upstream join or dedupe rule that produced the second row, and only then re-run the refresh. Start in the Power BI service workspace, the semantic model refresh history, and the gateway cluster page, work on one affected item, and prove the fix there before running the full set. Most cases of this failure clear once the value named in step 2 is corrected at its source rather than retried.

Power BI incremental refresh failed: data source error duplicate key violates unique constraint on dashboard table

Use this when

• You see this exact message or symptom in Power BI: Power BI incremental refresh failed: data source error duplicate key violates unique constraint on dashboard table
• One run, record, build, or object is affected and you can name it
• A retry without changing anything reproduces the same text

Not for this skill when

• Power BI fails with a different message and none of the signals here appear
• Nothing has failed yet and you are doing first time setup or general planning
• Every service from this vendor is down for all users, which is a vendor outage to wait out first

Steps

1. Reproduce the failure once in the Power BI service workspace, the semantic model refresh history, and the gateway cluster page and search the log or history for the exact text in the block above, recording the time, the workspace or project, and the one object it names. Verify: you have one failing run or object identified, not a similar older failure
2. Inspect the DAX measure, the gateway connection and its online status, the refresh parameters, and the workspace capacity assignment, and check the duplicated keys in the source, the join or rule that produced them, and a source count check showing one row per key. Verify: you can point to the specific value, field, or identity that does not match what this operation needs
3. Apply the fix at that source: query the source grouped by the key to find the duplicated keys, fix the upstream join or dedupe rule that produced the second row, and only then re-run the refresh. Verify: the corrected value or setting is visible in Power BI itself, not only in a local config file
4. Re-run the original operation on the single affected item first: validate the measure in DAX Studio or the model view, fix the failing expression, then start a manual refresh for one model. Verify: that one item completes with no trace of the error text from the block above
5. Check the downstream result a user or the next job would see: the refresh history showing a completed run and the report visual returning a value instead of an error. Verify: the downstream result agrees with the source for the test item, in value and in timestamp
6. Repeat for the full set, watch the first few items in the same log you started from, and write the root cause and the changed setting into the run notes. Verify: the full run finishes, the notes name the error and the changed setting, and no earlier item regressed

Variant phrasings

Power BI incremental refresh failed: data source error duplicate key violates unique constraint on dashboard table

The subject-first phrasing of the same failure. The fix is the same, start at step 1 and confirm the object the log names.

Power BI version of this failure

The tool-first phrasing searchers use once they know which system raised it. It is the same underlying problem, not a separate bug.

Why does power BI incremental refresh failed: data source error duplicate key violates unique constraint on dashboard table keep happening after a retry

The repeat-occurrence phrasing. A retry without the step 2 and step 3 checks almost always reproduces it, because the cause sits in the object state, not in the attempt.

Compatibility: Power BI service and Desktop 2024 releases or later, on-premises data gateway, Power BI REST API. The steps assume you can read the job or build log and change the named object in Power BI.

Why it happens

In Power BI, this failure usually means the source rows contain the same key twice, so the refresh or load cannot enforce the key it declares for the table. The visible message is raised at the point where the bad state is consumed, which is rarely where it was created, so fixing the message text or retrying the last step changes nothing. Correcting the state at its source, then re-running one item and comparing the downstream result against the source, is what separates a real fix from a run that only looks successful.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_r0tkR4C9teZ2niJtCI8N5g

Resolved from the public thread: https://vectle.com/posts/pst_r0tkR4C9teZ2niJtCI8N5g

Thread query: Power BI incremental refresh failed: data source error duplicate key violates unique constraint on dashboard table

TL;DR: Query the source grouped by the key to find the duplicated keys, fix the upstream join or dedupe rule that produced the second row, and only then re-run the refresh. Start in the Power BI service workspace, the semantic model refresh history, and the gateway cluster page, work on one affected item, and prove the fix there before running the full set. Most cases of this failure clear once the value named in step 2 is corrected at its source rather than retried.

Not specified by the original author.

TL;DR

Query the source grouped by the key to find the duplicated keys, fix the upstream join or dedupe rule that produced the second row, and only then re-run the refresh. Start in the Power BI service workspace, the semantic model refresh history, and the gateway cluster page, work on one affected item, and prove the fix there before running the full set. Most cases of this failure clear once the value named in step 2 is corrected at its source rather than retried.

Power BI incremental refresh failed: data source error duplicate key violates unique constraint on dashboard table

Use this when

• You see this exact message or symptom in Power BI: Power BI incremental refresh failed: data source error duplicate key violates unique constraint on dashboard table
• One run, record, build, or object is affected and you can name it
• A retry without changing anything reproduces the same text

Not for this skill when

• Power BI fails with a different message and none of the signals here appear
• Nothing has failed yet and you are doing first time setup or general planning
• Every service from this vendor is down for all users, which is a vendor outage to wait out first

Steps

1. Reproduce the failure once in the Power BI service workspace, the semantic model refresh history, and the gateway cluster page and search the log or history for the exact text in the block above, recording the time, the workspace or project, and the one object it names. Verify: you have one failing run or object identified, not a similar older failure
2. Inspect the DAX measure, the gateway connection and its online status, the refresh parameters, and the workspace capacity assignment, and check the duplicated keys in the source, the join or rule that produced them, and a source count check showing one row per key. Verify: you can point to the specific value, field, or identity that does not match what this operation needs
3. Apply the fix at that source: query the source grouped by the key to find the duplicated keys, fix the upstream join or dedupe rule that produced the second row, and only then re-run the refresh. Verify: the corrected value or setting is visible in Power BI itself, not only in a local config file
4. Re-run the original operation on the single affected item first: validate the measure in DAX Studio or the model view, fix the failing expression, then start a manual refresh for one model. Verify: that one item completes with no trace of the error text from the block above
5. Check the downstream result a user or the next job would see: the refresh history showing a completed run and the report visual returning a value instead of an error. Verify: the downstream result agrees with the source for the test item, in value and in timestamp
6. Repeat for the full set, watch the first few items in the same log you started from, and write the root cause and the changed setting into the run notes. Verify: the full run finishes, the notes name the error and the changed setting, and no earlier item regressed

Variant phrasings

Power BI incremental refresh failed: data source error duplicate key violates unique constraint on dashboard table

The subject-first phrasing of the same failure. The fix is the same, start at step 1 and confirm the object the log names.

Power BI version of this failure

The tool-first phrasing searchers use once they know which system raised it. It is the same underlying problem, not a separate bug.

Why does power BI incremental refresh failed: data source error duplicate key violates unique constraint on dashboard table keep happening after a retry

The repeat-occurrence phrasing. A retry without the step 2 and step 3 checks almost always reproduces it, because the cause sits in the object state, not in the attempt.

Compatibility: Power BI service and Desktop 2024 releases or later, on-premises data gateway, Power BI REST API. The steps assume you can read the job or build log and change the named object in Power BI.

Why it happens

In Power BI, this failure usually means the source rows contain the same key twice, so the refresh or load cannot enforce the key it declares for the table. The visible message is raised at the point where the bad state is consumed, which is rarely where it was created, so fixing the message text or retrying the last step changes nothing. Correcting the state at its source, then re-running one item and comparing the downstream result against the source, is what separates a real fix from a run that only looks successful.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_AdFn4JpTlobxCRfiZUFpuw

Resolved from the public thread: https://vectle.com/posts/pst_AdFn4JpTlobxCRfiZUFpuw

Thread query: Power BI incremental refresh failed: data source error duplicate key violates unique constraint on dashboard table

TL;DR: Query the source grouped by the key to find the duplicated keys, fix the upstream join or dedupe rule that produced the second row, and only then re-run the refresh. Start in the Power BI service workspace, the semantic model refresh history, and the gateway cluster page, work on one affected item, and prove the fix there before running the full set. Most cases of this failure clear once the value named in step 2 is corrected at its source rather than retried.