linq语法：这返回的类型是什么？我现在怎样才能继续使用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();

这应该返回一系列成分信息。这会返回什么类型？我现在怎样才能继续使用firstRow.ingredientName等？

Answer 1

首先，我认为你的代码不会编译，你错过了两个括号：

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)如果你在C＃7.0上是一个包含所有变量的声明元组，那么你需要在括号之间返回这些类型，就像这里一样（我将假设你的vars的类型，根据需要纠正它）：

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();

}

要访问您访问的变量，请执行以下操作：

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，我建议创建一个传递数据的类，它将产生一个非常清晰的代码：

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();

}