Entity Framework 多对多 - Code First - 迁移

Question

我有产品 class:

public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Language> Languages { get; set; }
}

语言class：

public class Language
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Product> Products { get; set; }

}

在我的 EntityTypeConfiguration 中：

public class ProductMap : EntityTypeConfiguration<Product>
{

    public ProductMap()
    {
        HasKey(m => m.Id);
        Property(p => p.Name).IsRequired();

       HasMany(p => p.Languages)
            .WithMany(l => l.Products)
            .Map(x => x.ToTable("ProducLanguages")
                .MapLeftKey("ProductId")
                .MapRightKey("LanguageId"));

        //Table  
        ToTable("Products");
    }
}

这按预期创建了第三个 table，但是当我使用以下种子执行我的更新数据库时：

protected override void Seed(EcoomerceContext context)
    {
        var languages = new List<Language>
        {
            new Language {Name = "Portuguese"},
            new Language {Name = "English"},
            new Language {Name = "Spanish"}
        };

        var languagePt = new List<Language>
        {
            new Language {Name = "Portuguese"},
        };

        //languages.ForEach(a => context.Languages.Add(a));

        new List<Product>
        {
          new Product {Name = "NameProduct1", Languages = languages},
          new Product {Name = NameProduct2 , Languages = languagePt},
        }.ForEach(a => context.Products.Add(a));

        context.SaveChanges();
    }

它像这样更新关系 table ProducLanguages：

正在插入一种不存在的语言（数字4），我期望的结果是：

我做错了什么？

提前致谢。

Answer 1

您需要指定每个实体的 Id，即使 PK 是身份。指定将在数据库中使用的 Id 至关重要，否则每个 Update-Database 都会创建新记录。

您还应该使用在 migrations.In 期间为播种数据创建的 AddOrUpdate 扩展方法，您可以指定一个表达式来了解应该使用什么属性来检查是否有必要执行 Add 或 Update 操作，但如果您未在实体中指定 Id，则会添加一个新行，而旧行也将保留。所以最后，你的 Seed 方法可能是这样的：

 protected override void Seed(ConsoleApplication3.YourContext context)
 {
        var languages = new[]
        {
            new Language {Id = 1, Name = "Portuguese"},
            new Language {Id = 2, Name = "English"},
            new Language {Id = 3, Name = "Spanish"},
            new Language {Id = 4, Name = "French"},
        };

        // This way you can add all the languages even when there is not associated to a product
        // The first parameter is an expression to know what properties should be used when determining whether an Add or Update operation should be performed
        context.Languages.AddOrUpdate(l => l.Name, languages);

        var products = new[]
        {
            new Product {Id = 1, Name = "NameProduct1", Languages = new List<Language> {languages[0],languages[1],languages[3]}},
            new Product {Id = 2, Name = "NameProduct2", Languages = new List<Language> {languages[0]}},
        };
        context.Products.AddOrUpdate(p=>p.Name,products);

        context.SaveChanges();
}

Entity Framework 多对多 - Code First - 迁移

Entity Framework many to many - Code First - Migrations

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migration

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