C# 实体框架，删除子项然后父项，DELETE 语句与 REFERENCE 约束冲突

Question

Trying to delete child items first, then the parent. I am inside the same using statement.

Originally I had one call to context.SaveChanges(); but I have changed to commit the child delete first, then try and delete the parent records, but I am still sometimes receiving this error message:

The DELETE statement conflicted with the REFERENCE constraint “FK_AccountQuestionMappings_AccountQuestions”. The conflict occurred in database “db”, table “dbo.AccountQuestionMappings”, column 'QuestionId'. The statement has been terminated.

So the relationship is the questions in table AccountQuestions are the parent, and these are mapped and stored in the AccountQuestionMappings table. I am trying to delete them from the AccountQuestionMappings table, then from the AccountQuestions table.

using (var db = dataContext())
{
    if(questionInfo != null)
    {
        var questionIds = db.AccountQuestions.Where(q => q.AccountQuestionInfoId == questionInfo.Id).Select(s => s.Id).ToList();

        foreach (var question in questionIds)
        {
            var questionMapping = db.AccountQuestionMappings.Where(q => q.QuestionId == question).FirstOrDefault();

            if (questionMapping != null)
            {
                db.AccountQuestionMappings.Remove(questionMapping);
            }
        }

        db.SaveChanges();

        db.AccountQuestions.RemoveRange(db.AccountQuestions.Where(s => s.AccountQuestionInfoId == questionInfo.Id));
        db.SaveChanges(); // error occurs on this line saying due to there still being a child in the mappings table
    }
}

Answer 1

You are using FirstOrDefault() to delete AccountQuestionMappings . So if there are multiple AccountQuestionMappings associated with AccountQuestions then it will only delete first one. So when you delete AccountQuestions it will throw error.

You can try updating code like below. Remove FirstOrDefault() . Update condition inside if statement. And use RemoveRange .

foreach (var question in questionIds)
{
    var questionMapping = db.AccountQuestionMappings.Where(q => q.QuestionId == question);

    if (questionMapping.Count() > 0)
    {
        db.AccountQuestionMappings.RemoveRange(questionMapping);
    }
}