c# - Entity Framework 5.0 - 1 对 1 关系无故为 NULL

Question

我在这里搜索了很多问题，听起来和我的很相似，但没有一个符合我的问题，所以我希望在这张票中得到一些帮助..

我使用 EF Code First 并尝试将其映射到现有(遗留)MySQL 数据库。在我的属性上工作正常，除了一个，我不明白为什么..

为空的模型:

[Table("einheitenstamm")]
public class Unit : ClassicEntity
{
    [Key]
    [Column("estID")]
    public int Id { get; set; }

    [Column("estEinheit")]
    public string Name { get; set; }
}

包含对 Unit 的引用的模型:

[Table("artikeldaten_preise")]
public class ArticlePrice : ClassicEntity
{
    [Key]
    [Column("id")]
    public int Id { get; set; }

    [Column("einheit")]
    [ForeignKey("Id")]
    public virtual Unit Unit { get; set; } /* is always null!!!!! */

    [Column("preisliste")]
    [ForeignKey("Id")]
    public virtual Pricelist Pricelist { get; set; } /* gets loaded without problems */

    [Column("artikel")]
    [ForeignKey("Id")]
    public virtual Article Article { get; set; } /* gets loaded without problems */


    [Column("preis")]
    public double Price { get; set; }
}

创建数据库表:

CREATE TABLE `artikeldaten_preise` (
    `id` INT(11) NOT NULL AUTO_INCREMENT,
    `preisliste` INT(11) NOT NULL,
    `artikel` VARCHAR(10) NOT NULL,
    `preis` DECIMAL(10,2) NOT NULL,
    `einheit` INT(11) NOT NULL,
    `changed` DATETIME NULL DEFAULT NULL,
    `sys_deleted` BIT(1) NOT NULL DEFAULT b'0',
    `sys_changedfrom` VARCHAR(50) NULL DEFAULT NULL,
    `sys_changedat` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY (`id`),
    INDEX `artikel` (`artikel`) USING BTREE,
    INDEX `preisliste` (`preisliste`) USING BTREE,
    INDEX `einheit` (`einheit`) USING BTREE
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
AUTO_INCREMENT=2;

代码:

var units = from unit in context.Units
            where unit.Id == 4
            select unit;

foreach (var unit in units)
    Console.WriteLine(unit.Id + ": " + unit.Name); /* works */


var prices = from price in context.ArticlePrices
             select price;

foreach (var price in prices.ToList()) /* price.Unit = NULL ........... */
    MessageBox.Show(price.Article.Description + " " + price.Price + "/"
                    + price.Unit.Name + " in pricelist '"
                    + price.Pricelist.Name + "'");

谁能告诉我我做错了什么？

Answer 1

您必须显式定义关系并为每个导航属性创建一个 xxId 属性，然后您可以使用相应的 ForeignKey 属性对其进行修饰。这里不需要“真正的”外键..

[Table("artikeldaten_preise")]
public class ArticlePrice : ClassicEntity
{
    [Key]
    [Column("id")]
    public int Id { get; set; }

    [Column("einheit")]
    public int UnitId { get; set; }

    [ForeignKey("UnitId")]
    public virtual Unit Unit { get; set; }

    [Column("preisliste")]
    public int PricelistId { get; set; }

    [ForeignKey("PricelistId")]
    public virtual Pricelist Pricelist { get; set; }

    [Column("artikel")]
    public int ArticleId { get; set; }

    [ForeignKey("ArticleId")]
    public virtual Article Article { get; set; }

    [Column("preis")]
    public double Price { get; set; }

}