Entity Framework Core and One-to-One Relation: Duplicate entry
.net ef-core-2.0 ef-core-2.1 entity-framework entity-framework-core
Question
There's One-to-One relationship:
builder.Entity<Models.Card>()
.HasOne<Models.Owner>()
.WithOne(c => c.Card)
.HasForeignKey<Models.Owner>("OwnerId");
At this moment
OwnerId = 1 has Card.Id = 333
and
OwnerId = 2 has Card.Id = 444
If try to change CardId for OwnerId = 1 to CardId = 444 I'll get an error like Duplicate entry ... for key ..., because OwnerId = 2 already has the same Card (Card.Id = 444).
What is the best way to prevent this behavior: to remove Card.Id = 444 from OwnerId = 2 and change CardId to requested for Owner 1?
Accepted Answer
yes; 1:1 is enforced via unique FK on one side, so the Owner.CardId property for OwnerId = 2 must first be changed to a different value (or that Owner record deleted).
Unless both sides of the relationship are optional (i.e. an Owner doesn't have to have a Card and a Card doesn't have to have an Owner), a shared primary key should be used (the optional side of the 1:? relationship's PK should also be a FK to the requried side's PK)
Popular Answer
First set the CardId for OwnerId to null (if this can be made as null), but again it will give you duplicate key if any other row has null value. So you have to delete the row for this ownerIdand then update the required row.
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