尝试保存新数据时发生未处理的异常(An unhandled exception occurred while trying to save new data)

我正在尝试保存我正在创建的问题和答案项目的更改更改。我无法保存标签，因为只要我查询数据是否已经存在，就会返回异常。

public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options) { } public DbSet<ApplicationUser> ApplicationUsers { get; set; } public DbSet<Question> Questions { get; set; } public DbSet<Tag> Tags { get; set; } public DbSet<QuestionTag> QuestionTags { get; set; } protected override void OnModelCreating(ModelBuilder modelBuilder) { base.OnModelCreating(modelBuilder); modelBuilder.Entity<QuestionTag>() .HasKey(t => new { t.QuestionID, t.TagID }); modelBuilder.Entity<QuestionTag>() .HasOne(qt => qt.Question) .WithMany(q => q.QuestionTags) .HasForeignKey(qt => qt.QuestionID); modelBuilder.Entity<QuestionTag>() .HasOne(qt => qt.Tag) .WithMany(t => t.QuestionTags) .HasForeignKey(qt => qt.TagID); }

这是我在查询标签是否已存在时用于解析新数据的代码。

public List<QuestionTag> ParseTags(string tags) { var tagList = tags.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).ToList(); var questionTags = new List<QuestionTag>(); var anyNewTags = false; foreach (var tag in tagList) { var tagExists = _context.Tags.Where(x => x.Name == tag) .Select(x => new QuestionTag { Tag = new Tag { Name = x.Name } }) .FirstOrDefault(); if (tagExists == null) { var newTag = new QuestionTag() { Tag = new Tag() { Name = tag } }; _context.QuestionTags.Add(newTag); questionTags.Add(newTag); anyNewTags = true; }else { questionTags.Add(tagExists); } } if (anyNewTags) _context.SaveChanges(); return questionTags; }

但是，当我尝试解析新的标记时，我得到此错误： InvalidOperationException：实体类型'QuestionTag'上的属性'QuestionID'具有临时值。 要么显式设置永久值，要么确保将数据库配置为为此属性生成值。

I'm trying to save the changes changes for a question and answer project I am creating. I can't save Tags because it returns an exception whenever I query if the data already exists.

Here is the code I use to Parse new Data while querying if the Tags already exist.

But Instead, I get this Error when I try to parse in new Tags: InvalidOperationException: The property 'QuestionID' on entity type 'QuestionTag' has a temporary value. Either set a permanent value explicitly or ensure that the database is configured to generate values for this property.

最满意答案

该错误指示您应该设置QuestionID属性以与Question实体建立混合。因此，尝试将值设置为QuestionId属性。

var newTag = new QuestionTag() { Tag = new Tag() { Name = tag }, QuestionId = questionId }; _context.QuestionTags.Add(newTag);

注意：我编写了questionId用于制作示例的questionId变量。您应该使用Question实体的相关ID进行设置。

The error directs you that you should set QuestionID property to establish assosication with Question entity. So try to set a value to QuestionId property.

var newTag = new QuestionTag() { Tag = new Tag() { Name = tag }, QuestionId = questionId }; _context.QuestionTags.Add(newTag);

Note : I wrote questionId variable for making an example. You should set it with related ID of Question entity.

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