我想做一个简单的查询来检索特定文章的组件数据+语言数据，然后将其放入viewmodel中。
ProductComponent 表是产品的子表，其中的相关字段是ComponentID和ProductId（外键，parentId），所以我想链接ProductComponents to Product和ProductTranslations，其中包含所有特定于语言的数据，因此我尝试在一个查询中完成所有操作以检索特定产品的组件列表。
以下是查询：
public IEnumerable<ProductComponents> ListComponents(int productid, string language)
{
var query = (from c in context.ProductComponents
from ct in context.ProductTranslations
where ct.ProductId == c.ComponentId
where ct.ProductLanguage == language
from cp in context.Product
where cp.ProductId == c.ComponentId
where c.ProductId == productid
select new EnumComponents
{
ProductId = c.ComponentId,
Name = ct.ProductName,
SKU = cp.SKU
});
return query;
}
这会产生此错误，并突出显示 return Query; 部分：
Cannot implicitly convert type 'System.Linq.IQueryable<Artikelhantering.Models.EnumComponents>' to 'System.Collections.Generic.IEnumerable<Artikelhantering.Models.ProductComponents>'. An explicit conversion exists (are you missing a cast?)
以下是大部分数据模型，根据我发现的谷歌搜索和浏览Stack Overflow，表之间的关系可能是罪魁祸首，所以我将大部分内容包括在内。
public class Product
{
[Key]
public int ProductId { get; set; }
[DisplayName("Article nr")]
public string SKU { get; set; }
[DisplayName("Product Category")]
public int ProductCategoriesId { get; set; }
[DisplayName("Alternative Category")]
public int? AdditionalCategoriesId { get; set; }
[DisplayName("Show purchase button?")]
public bool Purchase { get; set; }
[DisplayName("Show Product?")]
public bool ShowProduct { get; set; }
[DisplayName("Picture name")]
public string Picture { get; set; }
[DisplayName("Is reference product?")]
public bool Reference { get; set; }
[DisplayName("Inprice")]
public decimal inPrice { get; set; }
[DisplayName("Additional costs")]
public decimal AddCost { get; set; } /
[DisplayName("Weight in kg")]
public decimal Weight { get; set; }
[DisplayName("Volume in m^3")]
public decimal Volume { get; set; }
[DisplayName("Vat code, use 0")]
public decimal VAT { get; set; }
public virtual IList<ProductTranslations> ProductTranslations { get; set; }
public virtual IList<ProductPrices> ProductPrices { get; set; }
public virtual IList<ProductComponents> ProductComponents { get; set; }
public virtual IList<ProductAccessories> ProductAccessories { get; set; }
public virtual ProductCategories ProductCategories { get; set; }
public virtual ProductCampaigns ProductCampaigns { get; set; }
}
public class ProductTranslations
{
[Key]
public int ProductTranslationsId { get; set; }
public int ProductId { get; set; } // This one links to the Product class
[DisplayName("Language Code")]
public string ProductLanguage { get; set; }
[DisplayName("Description")]
public string Description { get; set; }
[DisplayName("Product Name")]
public string ProductName { get; set; }
[MaxLength(255)]
[DisplayName("Meta Keywords")]
public string MetaKeywords { get; set; }
[MaxLength(255)]
[DisplayName("Meta Description")]
public string MetaDescription { get; set; }
public virtual Product Product { get; set; }
}
public class ProductComponents
{
[Key]
public int ProductComponentsId { get; set; }
public int ProductId { get; set; }
public int ComponentId { get; set; }
public virtual IList<ProductTranslations> ProductTranslations { get; set; }
public virtual Product Product { get; set; }
}
然后我定义模型之间的关系：
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
modelBuilder.Entity<ProductCategories>()
.HasMany(x => x.ProductCategoriesTranslations) // Categories has many Translations
.WithRequired(y => y.ProductCategories) // Translations require a category
.HasForeignKey(p => p.ProductCategoriesId);
modelBuilder.Entity<Product>()
.HasMany(x => x.ProductPrices) // Product has many ProductPricings
.WithRequired(y => y.Product) // ProductPricing has required Product
.HasForeignKey(p => p.ProductId);
modelBuilder.Entity<Product>()
.HasMany(x => x.ProductTranslations) // Product has many ProductTranslations
.WithRequired(y => y.Product) // ProductTranslations has required Product
.HasForeignKey(p => p.ProductId);
modelBuilder.Entity<Product>()
.HasMany(x => x.ProductComponents) // Product has many ProductComponents
.WithRequired(y => y.Product) // ProductComponents has required Product
.HasForeignKey(p => p.ProductId);
modelBuilder.Entity<Product>()
.HasMany(x => x.ProductAccessories) // Product has many ProductAccessories
.WithRequired(y => y.Product) // ProductAccessories has required Product
.HasForeignKey(p => p.ProductId);
}
我猜我需要为ProductComponents和ProductTranslations和Product定义一个正确的关系，但我不太清楚如何，我已经尝试了各种方法来创建ProductComponents之间的关系 - ＆gt; ProductTranslations但没有任何成功。当然，问题可能就是其他问题。
答案 0 :(得分：0)
看起来我自己想出来了。现在它终于点击了非常简单明了的错误。关键是将公共IEnumerable＆lt; ListComponents＆gt; 重命名为public IEnumerable＆lt; EnumComponents＆gt;
回想起来似乎是合乎逻辑的，我应该在这里使用视图模型而不是模型，因为这就是我想要填充的东西，然后我可以从视图模型中调用模型就好了。
public IEnumerable<EnumComponents> ListComponents(int productid, string language)
{
//return context.ProductComponents.Where(m => m.ProductId == productid);
var query = (from c in context.ProductComponents
where c.ProductId == productid
select new EnumComponents
{
Name = c.ProductTranslations
.Where(i => i.ProductLanguage == language)
.Where(i => i.ProductId == c.ComponentId)
.Select(i => i.ProductName)
.Single(),
SKU = c.Product.SKU,
ProductId = c.ComponentId
});
return (query);
}