Why does InvalidOperationException get thrown when deleting some entity instances, while UpdateException gets thrown for others?

There can be two different exceptions because there are two layers where this check is applied. First if you mark an object as deleted and execute SaveChanges EF will check its internal storage where all loaded objects are tracked. If EF finds that any tracked order related to the deleted customer is also not marked as deleted it will fire an exception (probably InvalidOperationException ).

If there is no tracked related order EF will execute delete operation in the database where FK relation triggers an error. This error is captured by EF and an exception is throwm (probably UpdateException with inner database related exception).

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