string s = "";
 bool sCanBeNull = (s is Nullable);
 s = null;

sCanBeNull等于假吗？

我正在编写代码生成器,并且需要确保传递给它的每个类型都可以为空(如果还没有).

//Get the underlying type:
       var type = field.FieldValueType;

        //Now make sure type is nullable:
        if (type.IsValueType) 
        {
            var nullableType = typeof (Nullable<>).MakeGenericType(type);
            return nullableType.FullName;
        }
        else
        {
            return type.FullName;
        }

我是否需要明确检查字符串或我遗失了什么？

Nullable是一个通用结构,允许可空值的非可空值.

string不是Nullable

要判断某个类型是否具有空值,请使用以下事实：对于所有此类类型,默认值为null,而对于所有其他类型,它不是：

default(string) == null; // true

[ComplexType]
public partial class Company    
    public bool HasValue { get { return !string.IsNullOrEmpty(this.Name); } }

    [MaxLength(100)]
    public string Name { get; set; }

    [MaxLength(20)]
    public string PhoneNumber { get; set; }

    [MaxLength(128)]
    public string EmailAddress { get; set; }
}

我在这两个实体中重用它：

public partial class Customer
{
    public Customer ()
    {
        this.Company = new Company();       
    }

    [Key]
    public int IdCustomer { get; set; }

    [MaxLength(100)]
    [required]
    public string FirstName { get; set; }

    [MaxLength(100)]
    [required]
    public string LastName { get; set; }

    public Company Company { get; set; }

    public virtual AcademicInfo AcademicInfo { get; set; }
}


public partial class AcademicInfo
{       
    public AcademicInfo()
    {
        this.Organization = new Company();
    }       

    [Key,ForeignKey("Customer")]
    public int IdCustomer { get; set; }

    public Company Organization { get; set; }

    [MaxLength(100)]
    public string Subject { get; set; }

    [MaxLength(100)]
    public string Degree { get; set; }

    public virtual Customer Customer { get; set; }
}

在dbcontext的OnModelCreating中(编辑：为了简单起见,我添加了之前省略的FK代码)：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{    
    modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();

    // ... Other code here related to entities not related to the problem reported omitted to avoid confusion.

    modelBuilder.Entity<AcademicInfo>()
            .Hasrequired(a => a.Customer)
            .WithOptional(c => c.AcademicInfo)
            .WillCascadeOnDelete(true);

    modelBuilder.Entity<Customer>()
            .Property(p => p.Company.Name)
            .HasColumnName("CompanyName")
            .IsOptional(); // CONFLICT HERE
    modelBuilder.Entity<Customer>()
            .Property(p => p.Company.EmailAddress)
            .HasColumnName("CompanyEmailAddress")
            .IsOptional();  //CONFLICT HERE
    modelBuilder.Entity<Customer>()
            .Property(p => p.Company.PhoneNumber)
            .HasColumnName("CompanyPhoneNumber")
            .IsOptional();

    modelBuilder.Entity<AcademicInfo>()
            .Property(a => a.Organization.Name)
            .HasColumnName("OrganizationName")
            .Isrequired(); // CONFLICT
    modelBuilder.Entity<AcademicInfo>()
            .Property(a => a.Organization.EmailAddress)
            .HasColumnName("OrganizationEmail")
            .Isrequired(); // CONFLICT
    modelBuilder.Entity<AcademicInfo>()
            .Property(a => a.Organization.PhoneNumber)
            .HasColumnName("OrganizationPhone")
            .IsOptional();
}

Add-Migration命令失败,并显示以下错误：
为’Company’类型的属性’Name’指定了冲突的配置设置：
    IsNullable =与IsNullable = True的错误冲突

但它没有任何意义,因为我在AcademicInfo表中定义了不可为空的字段,在Customer表中定义了可为空的字段.

根据this issue,行为是关于如何配置特定复杂类型的实体框架限制.

This is a limitation of EF,some property facets need to be stored in C-Space and EF doesn’t have a way of configuring a particular usage of a complex type. So you can only specify different S-Space facets like ColumnName or ColumnType