Question

Question I’m trying something new here with a program I made earlier. In the first program I was able to drag and drop table adapters and use the generic “var” to store query results. Now I’m trying to create a new program that has some separation of code. For example in the first program I had all of the code written in the form.cs file, this time I’d like to create a class to run the queries and return them to the calling class, however, how do you store a query result that contains many types? You cant return a var variable, it must be more specific. I get an error on the select line that reads: “Cannot implicitly convert type’System.Collections.Generic.IEnumerable’ to ‘System.Collections.Generic.IEnumerable;. An explicit conversion exists(are you missing a cast?)

Can some one help me? What is the cast? The first method (public IEnumerable getList()) works as expected its the second method, (public IEnumerable getRecipeInfo(string recipeName)) where I get the error. Here’s my code so far.

namespace recipeDataBase
{
    class Query
    {
        recipiesNewDataSet recipeDataSet = new recipiesNewDataSet();
        recipiesNewDataSetTableAdapters.RecipeTableAdapter recipeTableAdapter = new recipiesNewDataSetTableAdapters.RecipeTableAdapter();
        recipiesNewDataSetTableAdapters.RecipeIngredientTableAdapter ingredientTableAdapter = new recipiesNewDataSetTableAdapters.RecipeIngredientTableAdapter();
        recipiesNewDataSetTableAdapters.RatingTableAdapter ratingTableAdapter = new recipiesNewDataSetTableAdapters.RatingTableAdapter();

        public  Query()
        {

        }

        public IEnumerable<string> getList()
        {
            recipeTableAdapter.Fill(recipeDataSet.Recipe);

            IEnumerable<string> recipeList = (from a in recipeDataSet.Recipe
                                              select a.RecipeName);
            return recipeList;
        }

        public IEnumerable<string> getRecipeInfo(string recipeName)
        {
            recipeTableAdapter.Fill(recipeDataSet.Recipe);
            ratingTableAdapter.Fill(recipeDataSet.Rating);
            ingredientTableAdapter.Fill(recipeDataSet.RecipeIngredient);
            IEnumerable<string> recipeInfo = (from a in recipeDataSet.Recipe
                                              from b in recipeDataSet.Rating
                                              from c in recipeDataSet.RecipeIngredient
                                              where a.RecipeName == recipeName &&
                                              a.RecipeNum == c.RecipeNum &&
                                              a.RatingNum == b.RatingNum
                                              select new { a.RecipeName, a.Nationality, a.Event, a.Source, b.FamilyRating, c.Ingredient });
            return recipeInfo;
        }

    }
}

Thanks in advance for any help!!

Answer 1

You’re getting an exception because you select an anonymous type in your query but the type of the query variable is IEnumerable<string>. Instead you must either select a string, use the var keyword or a custom class instead.

If you want to return something useful, i would create a custom class with all of these properties you have selected in the anonymous type, for example:

public class Recipe
{
    public String RecipeName{ get; set;}
    public String Nationality{ get; set;}
    public String Event{ get; set;}
    // ...
}

Then you can return an IEnumerable<Recipe> instead from the method and select instances in the query:

...
select new Recipe(){ RecipeName=a.RecipeName, Nationality=a.Nationality, Event=a.Event,... });

Side-note: I would suggest to use Join instead of Where in the query:

Why is LINQ JOIN so much faster than linking with WHERE?