可空属性到实体字段,实体框架通过Code First

Question

Required像这样使用数据注释:

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

将somefield设置为Not Null数据库,如何设置某个字段 以允许NULL？,我尝试通过SQL Server Management Studio设置它,但实体框架将其设置回Not Null.

Answer 1

只需省略属性中的[Required]属性即可string somefield.这将使它NULL在db中创建一个有能力的列.

要使int类型允许数据库中的NULL,必须在模型中将它们声明为可为空的int:

// 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允许列为null:

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

此代码应该在继承自的对象中DbContext.

Answer 3

在Ef .net core中，您可以执行两个选项；首先是数据注释：

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

或者使用流畅的api：

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; }
}

还有更多的细节在这里