I am trying to establish a hierarchical relationship between rows in an existing table. There are two fields of interest: a not-nullable primary key field id, and a second nullable field parentId.

Both these fields are pre-existing, and the normal case is that parentId will be null. This seems to be a normal use case, and in fact we have some old tables using the same pattern.

I am trying to use fluentMigrator to add a foreign key constraint after the fact on these rows:

Create.ForeignKey("C", "ParentId", "C", "CId").OnUpdate(Rule.None);

It is failing with the error:

The ALTER TABLE statement conflicted with the FOREIGN KEY SAME TABLE constraint "FK_C_ParentId". The conflict occurred in database "R", table "dbo.C", column 'CId'.

This is not a problem with illegal values, as I did a bulk update on the test system, and set all C.ParentId = null, and am still getting the same error.


1 Answer 1


If there are no illegal values in C.ParentID, then I am not clear what the problem might be. Is this Microsoft SQL Server?

I created a test case as follows:

Create Table dbo.Hier
(Id  INT IDENTITY Primary KEy,
 Other varchar(10));
 INSERT INTO dbo.Hier (ParID, Other) VALUES (NULL, 'Able');
 INSERT INTO dbo.Hier (ParID, Other) VALUES (1, 'Baker');
 INSERT INTO dbo.Hier (ParID, Other) VALUES (NULL, 'Charlie');
      CONSTRAINT FK_Parent
      FOREIGN    KEY (ParID)
      REFERENCES Hier(ID);
INSERT INTO dbo.Hier (ParID, Other) VALUES (3, 'Delta');
SELECT * FROM dbo.Hier;
DROP TABLE dbo.Hier;

Seems to work fine. If you are on a different SQL Server it might have different behavior. Or fluentMigrator may have a problem.

  • This is microsoft SQL server, running locally with the database, and at the moment. There aren't any values at all, because I blew them all a way. Must be a migrator problem then, because if I drop the table and re-add, it builds just fine. Thanks for the quick response.
    – ElizabethH
    Commented Sep 20, 2013 at 15:02

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