[backport release/2.0] fix: don't enforce many-to-one/one-to-many relationships for DWSQL (#3770) - #3775
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Pull request overview
This backport fixes an incorrect GraphQL schema nullability assumption for Fabric Warehouse (DWSQL): because DWSQL does not enforce foreign keys, relationship fields must not be marked non-nullable based solely on NOT NULL FK metadata, otherwise valid queries can fail with HC0018 (“Cannot return null for non-nullable field.”).
Changes:
- Thread
DatabaseTypethrough SQL GraphQL schema generation so relationship nullability decisions can be database-specific. - For
DatabaseType.DWSQL, force relationship fields to be nullable when generating the GraphQL schema. - Add/extend unit tests to validate DWSQL vs MSSQL relationship-field nullability behavior.
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Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| src/Service.Tests/GraphQLBuilder/Sql/SchemaConverterTests.cs | Adds coverage asserting DWSQL relationship fields become nullable even when FK metadata indicates NOT NULL, while MSSQL remains unchanged. |
| src/Service.GraphQLBuilder/Sql/SchemaConverter.cs | Adds databaseType plumbing and makes FindNullabilityOfRelationship return nullable for DWSQL relationships. |
| src/Core/Services/GraphQLSchemaCreator.cs | Passes the metadata provider’s DatabaseType into SchemaConverter during schema construction (including linking entities). |
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…3770) ## What's the problem? When Data API builder serves a Fabric Warehouse (DWSQL) database, a GraphQL query that follows a relationship between two tables could fail with this error: ``` "Cannot return null for non-nullable field." (HC0018) ``` ...even when the query was perfectly valid and the data was fine. Instead of returning the row, the whole query blew up. ## Why does it happen? Most databases guarantee that if a row points to a "parent" row (a foreign key), that parent actually exists. DAB relies on that guarantee: if a foreign-key column is marked "required" (NOT NULL), DAB assumes the related object is always there, and tells GraphQL "this related field will never be null." **Fabric Warehouse is different — it does not enforce foreign keys.** So a child row can happily point at a parent that doesn't exist (an "orphaned" row). When GraphQL asks for that missing parent, DAB has nothing to return, but it already promised the field would never be null. GraphQL sees a broken promise and throws HC0018. Example: an `Enrollment` row has a `studentId` that no `Student` matches. Asking for `enrollment.student` returns nothing, and the query fails. ## What does this change do? For Fabric Warehouse (DWSQL) only, DAB no longer assumes related rows always exist. It marks the related fields on many-to-one and one-to-many relationships as nullable. That way, when a related row is genuinely missing, the query simply returns `null` for that field instead of failing the entire request. Behavior for all other databases (SQL Server, PostgreSQL, MySQL) is unchanged, since they do enforce foreign keys. ## How was it verified? - Added unit tests covering both DWSQL (field is now nullable) and SQL Server (field stays non-nullable) for both relationship directions. - Manually validated end-to-end against a Fabric Warehouse: the query that previously failed now returns the row with `student: null`. #### Before <img width="854" height="730" alt="Screenshot 2026-08-12 143540" src="https://github.com/user-attachments/assets/9b4585e5-5cb8-456f-8efb-0eda22f68994" /> #### After <img width="1053" height="514" alt="Screenshot 2026-08-12 141456" src="https://github.com/user-attachments/assets/cbb42b63-c867-4804-bc10-6d7a4c1c643b" /> --------- Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com> Co-authored-by: aaronburtle <93220300+aaronburtle@users.noreply.github.com>
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…3770) ## What's the problem? When Data API builder serves a Fabric Warehouse (DWSQL) database, a GraphQL query that follows a relationship between two tables could fail with this error: ``` "Cannot return null for non-nullable field." (HC0018) ``` ...even when the query was perfectly valid and the data was fine. Instead of returning the row, the whole query blew up. ## Why does it happen? Most databases guarantee that if a row points to a "parent" row (a foreign key), that parent actually exists. DAB relies on that guarantee: if a foreign-key column is marked "required" (NOT NULL), DAB assumes the related object is always there, and tells GraphQL "this related field will never be null." **Fabric Warehouse is different — it does not enforce foreign keys.** So a child row can happily point at a parent that doesn't exist (an "orphaned" row). When GraphQL asks for that missing parent, DAB has nothing to return, but it already promised the field would never be null. GraphQL sees a broken promise and throws HC0018. Example: an `Enrollment` row has a `studentId` that no `Student` matches. Asking for `enrollment.student` returns nothing, and the query fails. ## What does this change do? For Fabric Warehouse (DWSQL) only, DAB no longer assumes related rows always exist. It marks the related fields on many-to-one and one-to-many relationships as nullable. That way, when a related row is genuinely missing, the query simply returns `null` for that field instead of failing the entire request. Behavior for all other databases (SQL Server, PostgreSQL, MySQL) is unchanged, since they do enforce foreign keys. ## How was it verified? - Added unit tests covering both DWSQL (field is now nullable) and SQL Server (field stays non-nullable) for both relationship directions. - Manually validated end-to-end against a Fabric Warehouse: the query that previously failed now returns the row with `student: null`. #### Before <img width="854" height="730" alt="Screenshot 2026-08-12 143540" src="https://github.com/user-attachments/assets/9b4585e5-5cb8-456f-8efb-0eda22f68994" /> #### After <img width="1053" height="514" alt="Screenshot 2026-08-12 141456" src="https://github.com/user-attachments/assets/cbb42b63-c867-4804-bc10-6d7a4c1c643b" /> --------- Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com> Co-authored-by: aaronburtle <93220300+aaronburtle@users.noreply.github.com> Backport of #3770 to release/2.0.
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What's the problem?
When Data API builder serves a Fabric Warehouse (DWSQL) database, a GraphQL query that follows a relationship between two tables could fail with this error:
...even when the query was perfectly valid and the data was fine. Instead of returning the row, the whole query blew up.
Why does it happen?
Most databases guarantee that if a row points to a "parent" row (a foreign key), that parent actually exists. DAB relies on that guarantee: if a foreign-key column is marked "required" (NOT NULL), DAB assumes the related object is always there, and tells GraphQL "this related field will never be null."
Fabric Warehouse is different — it does not enforce foreign keys. So a child row can happily point at a parent that doesn't exist (an "orphaned" row). When GraphQL asks for that missing parent, DAB has nothing to return, but it already promised the field would never be null. GraphQL sees a broken promise and throws HC0018.
Example: an
Enrollmentrow has astudentIdthat noStudentmatches. Asking forenrollment.studentreturns nothing, and the query fails.What does this change do?
For Fabric Warehouse (DWSQL) only, DAB no longer assumes related rows always exist. It marks the related fields on many-to-one and one-to-many relationships as nullable. That way, when a related row is genuinely missing, the query simply returns
nullfor that field instead of failing the entire request.Behavior for all other databases (SQL Server, PostgreSQL, MySQL) is unchanged, since they do enforce foreign keys.
How was it verified?
student: null.Before
After