linq语法：返回的类型是什么？现在如何继续使用firstRow.ingredientName等？

Question

以下是我的linq表达式：

return from c in db.RecipeIngredients
       join d in db.Ingredients on c.IngredientID equals d.IngredientsID
       where c.RecipeID.Equals(recipeID)
       select (d.IngredientsID,c.Unit,c.IngredientID,c.Amount).ToList();

这应该返回成分信息行的列表。返回的类型是什么？现在如何继续使用firstRow.ingredientName等？

Answer 1

首先，我认为您的代码无法编译，您缺少两个括号：

return (from c in db.RecipeIngredients
   join d in db.Ingredients on c.IngredientID equals d.IngredientsID
   where c.RecipeID.Equals(recipeID)
   select (d.IngredientsID,c.Unit,c.IngredientID,c.Amount)).ToList();

好的，接下来，(d.IngredientsID,c.Unit,c.IngredientID,c.Amount)如果您使用的是C＃7.0，它是一个包含所有变量的声明性元组，那么您需要在括号之间返回该类型，例如此处（我将假设您的var类型，请根据需要对其进行更正）：

public List<(int, UnitNames, int, double)> GetRecipe(int recipeId)
{
    return (from c in db.RecipeIngredients
       join d in db.Ingredients on c.IngredientID equals d.IngredientsID
       where c.RecipeID.Equals(recipeID)
       select (d.IngredientsID,c.Unit,c.IngredientID,c.Amount)).ToList();

}

要访问变量，您需要像这样：

var recipe = GetRecipe(recipeId);

foreach(var ingredient in recipe)
{
    var ingredientsId = ingredient.Item1;
    var unit = ingredient.Item2;
    var ingredientId = ingredient.Item3;
    var amount = ingredient.Item4;
}

无论如何，我建议创建一个类来传递数据，这将导致非常清晰的代码：

public class Ingredient
{
    public int IngredientsId { get; set; }
    public UnitNames Unit { get; set; }
    public int IngredientId { get; set; }
    public double Amount { get; set; }
}

public List<Ingredient> GetRecipe(int recipeId)
{
    return (from c in db.RecipeIngredients
       join d in db.Ingredients on c.IngredientID equals d.IngredientsID
       where c.RecipeID.Equals(recipeID)
       select new Ingredient { 
                                 IngredientsId = d.IngredientsID, 
                                 Unit = c.Unit,
                                 IngredientId = c.IngredientID, 
                                 Amount = c.Amount 
                             }).ToList();

}