我有以下代码:
public List<Product> ListAll()
{
List<Product> products = new List<Product>();
var db_products = db.Products
.Where(p => p.Enabled == true)
.OrderBy(p => p.Name)
.Select(p => new
{
ProductId = p.ProductId,
Name = p.Name,
...
})
.ToList();
foreach (var dbP in db_products)
{
Product p = new Product();
p.ProductId = dbP.ProductId;
p.Name = dbP.Name;
...
products.Add(p);
}
return products;
}
它如我所愿地工作,因为它成功地返回了一个产品对象列表。不过,有没有没有 foreach 循环的方法,所以我可以立即转换它?
我试过:
public List<Product> ListAll()
{
List<Product> products = db.Products
.Where(p => p.Visible == true)
.OrderBy(p => p.Name)
.Select(p => new
{
ProductId = p.ProductId,
Name = p.Name,
...
})
.AsEnumerable()
.Cast<Product>()
.ToList();
return products;
}
和
public List<Product> ListAll()
{
List<Product> products = db.Products
.Where(p => p.Visible == true)
.OrderBy(p => p.Name)
.Select(p => new Product
{
ProductId = p.ProductId,
Name = p.Name,
...
})
.ToList();
return products;
}
但两者都不起作用。对于第二个,我收到以下错误:
at System.Data.Objects.ELinq.ExpressionConverter.CheckInitializerType(Type type)
at System.Data.Objects.ELinq.ExpressionConverter.MemberInitTranslator.TypedTranslate(ExpressionConverter parent, MemberInitExpression linq)
at System.Data.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
at System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
at System.Data.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input)
at System.Data.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input, DbExpressionBinding& binding)
at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, DbExpression& source, DbExpressionBinding& sourceBinding, DbExpression& lambda)
at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SelectTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod)
at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)
at System.Data.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
at System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
at System.Data.Objects.ELinq.ExpressionConverter.Convert()
at System.Data.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
at System.Data.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
at System.Data.Objects.ObjectQuery`1.System.Collections.Generic.IEnumerable<T>.GetEnumerator()
at System.Data.Entity.Internal.Linq.InternalQuery`1.GetEnumerator()
at System.Data.Entity.Infrastructure.DbQuery`1.System.Collections.Generic.IEnumerable<TResult>.GetEnumerator()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at SeashellBrawlCorvee...ListAll() in c:\Users\...\Documents\Visual Studio 2012\Projects\seashell-brawl-corvee\seashell-brawl-corvee\...\ProductController.cs:line 149
at SeashellBrawlCorvee...ProductsRepository..ctor() in c:\Users\...\Documents\Visual Studio 2012\Projects\seashell-brawl-corvee\seashell-brawl-corvee\...\ProductsRepository.cs:line 21
at SeashellBrawlCorvee...ProductsController..cctor() in c:\Users\...\Documents\Visual Studio 2012\Projects\seashell-brawl-corvee\seashell-brawl-corvee\...\ProductsController.cs:line 16
如果有人知道解决方案,我将不胜感激,否则我将坚持使用 foreach 循环。
预先感谢您的回复。
最佳答案
当你从一个ORM调用一个方法时,它可以返回一个代理,所以,当web api需要反序列化它时,你会遇到很多问题。
一种方法是创建一个 ViewModel
.例如,使用您需要的信息创建一个类:
public class ProductViewModel
{
public int Id { get; set; }
public string Name { get; set; }
// properties
}
当您查询数据时,尝试返回 List<ProductViewModel>
, 例如:
return db.Products
.Where(p => p.Visible == true)
.OrderBy(p => p.Name)
.Select(p => new ProductViewModel() { Id = p.ProductId, Name = p.Name })
.ToList();
使用 ViewModel
暴露于 View
或 Request
是一个很好的实践。
关于C# Web API LINQ 实体查询 - 将 AnonymousType 转换为类对象,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23367736/