實體或複雜類型不能在LINQ to Entities查詢中構造？

Question

這裏是我的代碼，我希望有人能賜教：

public async Task<ActionResult> Search() 
{ 
    NameValueCollection filter = HttpUtility.ParseQueryString(Request.Params.ToString()); 

    string term = filter["term"]; 
    var query = db.ProductGraphicsCards 
    .Where(pgc => pgc.GraphicsCardSKU.StartsWith(term)) 
    .Select(pgc => new ProductGraphicsCard() 
    { 
     GraphicsCardSKU = pgc.GraphicsCardSKU, 
     GraphicsCardMemory = pgc.GraphicsCardMemory 
    }; 

    var products = await query.ToListAsync(); 

    List<string> items = new List<string>(); 

    foreach (var product in products) 
    { 
     items.Add(product.GraphicsCardSKU + "/" + product.GraphicsCardMemory.ToString()); 
    } 

    return Json(items, JsonRequestBehavior.AllowGet); 
} 

給我的錯誤，我不明白爲什麼

Answer 1

var query = db.ProductGraphicsCards 
    .Where(pgc => pgc.GraphicsCardSKU.StartsWith(term)) 
    .Select(pgc => new ProductGraphicsCard() 
    { 
     GraphicsCardSKU = pgc.GraphicsCardSKU, 
     GraphicsCardMemory = pgc.GraphicsCardMemory 
    }; 

我想這個問題就在這裏。您將無法將結果提取到映射實體ProductGraphicsCard。嘗試提取到未映射的DTO或匿名類型。

var query = db.ProductGraphicsCards 
    .Where(pgc => pgc.GraphicsCardSKU.StartsWith(term)) 
    .Select(pgc => new { 
     pgc.GraphicsCardSKU, 
     pgc.GraphicsCardMemory 
    }; 

Answer 2

這裏

.Select(pgc => new ProductGraphicsCard()

你想投影到實體類中。我不知道爲什麼，但它不支持實體框架（因此NotSupportedException）。要解決這個問題

的方法之一是投影到匿名類型：

var query = db.ProductGraphicsCards 
    .Where(pgc => pgc.GraphicsCardSKU.StartsWith(term)) 
    .Select(pgc => new 
    { 
     GraphicsCardSKU = pgc.GraphicsCardSKU, 
     GraphicsCardMemory = pgc.GraphicsCardMemory 
    }; 

var products = await query.ToListAsync(); 

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