关于c#：如何在Entity Framework Core中配置多对多关系

How to configure a Many To Many relationship in Entity Framework Core

我有一些文章和一些作者，并希望将它们链接为：

任何文章都可以有任意数量的作者，并且
每个作者可以写任意数量的文章

我使用此教程创建了ManyToMany关系：https：//www.learnentityframeworkcore.com/configuration/many-to-many-relationship-configuration

这是我定义班级的方式。

文章

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public class Article
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ID { get; set; }

public string Title { get; set; }

public DateTime Date { get; set; }

public ICollection<ArticleAuthor> ArticleAuthors { get; set; }
}

作者

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public class Author
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ID { get; set; }

[Column(TypeName ="text")] public string Name { get; set; }

[Column(TypeName ="text")] public string Email { get; set; }

public ICollection<ArticleAuthor> ArticleAuthors { get; set; }
}

ArticleAuthor

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public class ArticleAuthor
{
public int ArticleId { get; set; }

public Article Article { get; set; }

public int AuthorId { get; set; }

public Author Author { get; set; }
}

DbContext

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public class AppDbContext : DbContext
{
public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
{
}

public DbSet<Article> Articles { get; set; }

public DbSet<Author> Authors { get; set; }

public DbSet<ArticleAuthor> ArticleAuthors { get; set; }

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<ArticleAuthor>()
.HasKey(bc => new {bc.ArticleId, bc.AuthorId});
modelBuilder.Entity<ArticleAuthor>()
.HasOne(bc => bc.Article)
.WithMany(b => b.ArticleAuthors)
.HasForeignKey(bc => bc.ArticleId);
modelBuilder.Entity<ArticleAuthor>()
.HasOne(bc => bc.Author)
.WithMany(c => c.ArticleAuthors)
.HasForeignKey(bc => bc.AuthorId);
}
}

在我运行dotnet ef数据库更新后，将按预期创建表。

一切似乎都很好，除了当我尝试通过此服务与作者添加文章时：

服务

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// POST: api/Articles
[HttpPost]
public async Task<IActionResult> PostArticle([FromBody] Article article)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}

_context.Articles.Add(article);
await _context.SaveChangesAsync();

return Ok(article);
}

JSON

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{
"Title":"Title 2",
"ReadingTime" : 2,
"Date":"01.12.2019",
"Theme":"1",
"ArticleAuthors":[
{
"ID":"1"
}
]
}

当我尝试与作者添加文章时，我一直被这个错误困扰

System.InvalidOperationException: The property 'AuthorId' on entity type 'ArticleAuthor' has a temporary value. Either set a permanent value explicitly or ensure that the database is configured to generate values for this property.