实体框架迁移中必填字段的默认值？ [英] Default value for Required fields in Entity Framework migrations?

问题描述

我已经在 [Required] 数据注释到我的一个模型中mvc-4 / get-started-with-aspnet-mvc4 / add-validation-to-the-modelrel =noreferrer> ASP.NET MVC应用程序。创建迁移后，运行 update-database 会出现以下错误：

I've added [Required] data annotation to one of my models in ASP.NET MVC application. After creating a migration, running update-database resuilts in the following error:

无法将值NULL插入列Director，表
'MOVIES_cf7bad808fa94f89afa2e5dae1161e78.dbo.Movies';列不
允许空值。 UPDATE失败。该陈述已被终止。

Cannot insert the value NULL into column 'Director', table 'MOVIES_cf7bad808fa94f89afa2e5dae1161e78.dbo.Movies'; column does not allow nulls. UPDATE fails. The statement has been terminated.

这是由于某些记录在 Director 列。如何自动将这些值自动更改为某些默认值（例如John Doe）导演？

This is due to some records having NULL in their Director columns. How can I automatically change those values to some default (say "John Doe") director?

这是我的模型：

  public class Movie
    {
        public int ID { get; set; }
        [Required]
        public string Title { get; set; }

        [DataType(DataType.Date)]
        public DateTime ReleaseDate { get; set; }

        [Required]
        public string Genre { get; set; }

        [Range(1,100)]
        [DataType(DataType.Currency)]
        public decimal Price { get; set; }

        [StringLength(5)]
        public string Rating { get; set; }

        [Required]     /// <--- NEW
        public string Director { get; set; }
    }

这里是我最新的迁移：

public partial class AddDataAnnotationsMig : DbMigration
{
    public override void Up()
    {
        AlterColumn("dbo.Movies", "Title", c => c.String(nullable: false));
        AlterColumn("dbo.Movies", "Genre", c => c.String(nullable: false));
        AlterColumn("dbo.Movies", "Rating", c => c.String(maxLength: 5));
        AlterColumn("dbo.Movies", "Director", c => c.String(nullable: false));
    }

    public override void Down()
    {
        AlterColumn("dbo.Movies", "Director", c => c.String());
        AlterColumn("dbo.Movies", "Rating", c => c.String());
        AlterColumn("dbo.Movies", "Genre", c => c.String());
        AlterColumn("dbo.Movies", "Title", c => c.String());
    }
}

推荐答案

我记得正确的是，这样的东西应该可以工作：

If I remember correctly, something like this should work:

AlterColumn("dbo.Movies", "Director", c => c.String(nullable: false, defaultValueSql: "John Doe"));

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