Question

使用数据注释 要求 如:

[Required]
public int somefield {get; set;}

Will set somefield to Not Null in database, How can I set somefield to allow NULLs?, I tried setting it through SQL Server Management Studio but Entity Framework set it back to Not Null.

Answer 1

从 strection somefield 属性的 字符串中略去[要求]属性。这样它就可以在 db 中创建一个 NULLL 可操作的列。



要让内型允许数据库中的NULLs, 就必须在模型中宣布这些 LLs为无效符号 :

// an int can never be null, so it will be created as NOT NULL in db
public int someintfield { get; set; }

// to have a nullable int, you need to declare it as an int?
// or as a System.Nullable<int>
public int? somenullableintfield { get; set; }
public System.Nullable<int> someothernullableintfield { get; set; }

Answer 2

另一个选项是告诉 EF 允许栏目无效:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
        modelBuilder.Entity<SomeObject>().Property(m => m.somefield).IsOptional();            
        base.OnModelCreating(modelBuilder);
}

此代码应位于 DbContext 的继承对象中。

Answer 3

在 Ef.net 核心中,您可以选择两种选择:首先用数据说明:

public class Blog
{
    public int BlogId { get; set; } // optinal case

    [Required]
    public string Url { get; set; } // required case
}

或流利的:

class MyContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Blog>()
            .Property(b => b.Url)
            .IsRequired(false)//optinal case
            .IsRequired()//required case
            ;
    }
}

public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }
}

详情请见"https://learn.microsoft.com/en-us/ef/core/modeling/required-optional" rel="norefererr">这里

Answer 4

Jon s 回答没有为我工作,因为我有一个编译器错误 CS0453 C# 类型必须是不可计算值类型, 才能使用它作为通用类型或方法的参数 T

这对我管用:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<SomeObject>().HasOptional(m => m.somefield);
    base.OnModelCreating(modelBuilder);
}

友情链接