LINQ Selecting a List within a List

Question

I'm trying to fill a list within a list using LINQ to query my database.

The issue I'm facing is that I'm unsure how to select the data into the child list.

When trying to execute the code below, I receive the error

Error 1 Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Collections.Generic.IEnumerable'. An explicit conversion exists (are you missing a cast?)

The model classes are like so:

public class _LayoutViewModel
{
    public List<CallGuideMenuL1> CGL1 { get; set; }
}

public class CallGuideMenuL1
{
    public string Area { get; set; }
    public List<CallGuideMenuL2> Products { get; set; }
}

public class CallGuideMenuL2
{
    public int CallGuideProductId { get; set; }
    public string Product { get; set; }
}

And the DB context:

public class CallGuideArea
{
    public int CallGuideAreaId { get; set; }
    public string Area { get; set; }
    public List<CallGuideProduct> CallGuideProducts { get; set; }
}

public class CallGuideProduct
{
    public int CallGuideProductId { get; set; }
    public string Product { get; set; }
    public int CallGuideAreaId { get; set; }
    public DateTime Added { get; set; }
    public DateTime? Deleted { get; set; }
}

In my controller I'm trying to select the data like so:

_LayoutViewModel vm = new _LayoutViewModel();

vm.CGL1 = from a in db.CallGuideArea
            .SelectMany(p => p.CallGuideProducts)
            select a;

I'm pretty sure it's the select a; line that's the issue as I need to assign the data back to the properties of both CallGuideMenuL1 and CallGuideMenuL2.

Could anyone point me in the right direction around the right LINQ expression?

if vm.CGL1 is IList<CallGuideProducts> you can try with vm.CGL1 = db.CallGuideArea.SelectMany(p=>p.CallGuideProducts).ToList(); — Rodrigo Juarez
– Rodrigo Juarez, Commented Apr 18, 2015 at 15:00
@GiorgiNakeuri vm.CGL1 is the view model class, I've updated the question to include it sorry. — Gareth
– Gareth, Commented Apr 18, 2015 at 15:04
Are you trying to map CallGuideArea objects to CallGuideMenuL1? — Rodrigo Juarez
– Rodrigo Juarez, Commented Apr 18, 2015 at 15:07

Gareth · Accepted Answer · 2020-03-19 00:26:28Z

3

vm.CGL1 = db.CallGuideArea.Select(a => new CallGuideMenuL1()
{
    Area = a.Area,
    Products = a.CallGuideProducts.Select(p => new CallGuideMenuL2()
    {
        CallGuideProductId = p.CallGuideProductId,
        Product = p.Product
    }).ToList()
}).ToList();

edited Mar 19, 2020 at 0:26

Gareth

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answered Apr 18, 2015 at 15:19

Rodrigo Juarez

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Comments

Giorgi Nakeuri · Accepted Answer · 2015-04-18 15:09:48Z

0

Probably vm.CGL1 is declared as List so you need to select into List:

vm.CGL1 = (from a in db.CallGuideArea
            .SelectMany(p => p.CallGuideProducts)
            select a).ToList();

or you will need to project:

vm.CGL1 = (from a in db.CallGuideArea
            .SelectMany(p => p.CallGuideProducts)
            select new CallGuideMenuL1()
            {
               Area = a.--some property
               ...
            }).ToList();

edited Apr 18, 2015 at 15:09

answered Apr 18, 2015 at 15:04

Giorgi Nakeuri

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1 Comment

Gareth Over a year ago

Thanks for your answer. The only issue with the projection is that a doesn't include the data from CallGuideArea.

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