C# - Cannot Implicitly Convert Type List<Product> to List<Iproduct>

C# - Cannot implicitly convert type ListProduct to ListIProduct

Yep it's a covariance limitation in C#. You can't convert a list of one type to a list of another.

Instead of:

List<contracts.IProduct> myList = new List<dto.Product>();

You have to do this

List<contracts.IProduct> myList = new List<contracts.IProduct>();

myList.Add(new dto.Product());

Eric Lippert explains why they implemented it this way:
http://blogs.msdn.com/ericlippert/archive/tags/Covariance+and+Contravariance/default.aspx (archived)

(And why it is different than working with arrays of items).

Cannot implicitly convert type System.Collections.Generic.ListDerivedDataClass to System.Collections.Generic.ListBaseDataClass

The data list needs to be of type List<BaseDataClass> rather than List<DerivedDataClass>.

For example, this will compile:

List<BaseDataClass> data = new List<DerivedDataClass>().Select(x => (BaseDataClass)x).ToList();

You can create a list and add items like so:

List<BaseDataClass> data = new List<BaseDataClass>();
data.Add(new DerivedDataClass());

Cannot implicitly convert type ListClass to ListOtherClass error

The return type must match what you are returing

So change

public List<OrgElementViewModel> ChildrenComboDataset

To

public List<OrgChartManager> ChildrenComboDataset

And it will become:

    private List<OrgChartManager> myList;
    public List<OrgChartManager> ChildrenComboDataset
    {
        get
        {

            IEnumerable myEnumerable  = OrgChartManager.Instance().GetChildrenSerch();
            myList = myEnumerable.Cast<OrgChartManager>().ToList();
            return myList; // You are returing List<OrgChartManager>

        }
    }

Cannot implicitly convert type Listanonymous type: .. to IEnumerableProduct

Its seems that your expected return output is combination of both Product and ProductType model class. So make a DTO (Data Transfer Object) class as follows which will contain all the fields of your output query.

public class ProductDto
{
    public long ProductId { get; set; }
    public string Number { get; set; }
    public double Amount { get; set; }
    public double PrimeCostEUR { get; set; }
    public string ProductTypeName { get; set; }
}

Now write your controller method as follows where return type of the method is IEnumerable<ProductDto>:

public async Task<IEnumerable<ProductDto>> TestProducts()
{
    var items = await _context.Products.Select(p => new ProductDto
         {
             ProductId= p.ProductId,
             Number= p.Number,
             Amount= p.Amount,
             PrimeCostEUR= p.PrimeCostEUR,
             ProductTypeName = p.ProductType.NameType
         }).ToListAsync();
    return items;
}

Moreover you don't need explicit LINQ join as you did, you can achieve the same thing using EF projection as I have done with more simplicity.

Cannot implicitly convert type 'string' to 'System.Collections.Generic.Liststring' c# class getter

Change the return type of the getter to string instead of List<string>.

public string Food  // <-- return type should be string, not List<string>
{
    get {
        string aliments = "";
        foreach (string aliment in Food)
        {
            aliments += $"{aliment} ";
        }
        return aliments;
    }
}

Cannot implicitly convert type 'System.Collections.Generic.List in asp mvc

Use this:

var qstudent = from s in _db.Tbl_Students
    join pr in _db.Tbl_Pye_Reshte on s.StudentID equals pr.StudentID
    join r in _db.Tbl_Reshte on pr.ReshteID equals r.ReshteID
    join p in _db.Tbl_Paye on pr.PayeID equals p.PayeID
    orderby p.PayeID descending
    select new Tbl_Students { StudentName = s.StudentName, StudentFamily = s.StudentFamily, StudentImage = s.StudentImage, StudentPayeName = p.PayeName, StudentReshtName = r.ReshteName };
return qstudent.ToList();

Select new { ... } will just create an anonymous type whch can´t be converted to anything except object.

Just as an aside: you should consider naming your types depending on what an entity is within your application, in your example Student, not the table where the entity is stored.

Error: “Cannot implicitly convert type”

The return type of your method is TimeWorkMonthlies but inside the method body return List<TimeWorkMonthlies>

You should either

1. change your method return type to IEnumerable<TimeWorkMonthlies>
   (You could use List<TimeWorkMonthlies> but using an interface to abstract a collection type is better for many reasons)
2. Use FirstOrDefault, First, SingleOrDefault or Single extension methods of IEnumerable if you aim to return only one element and you do not care about anything except for the first element

Which of those methods is better depends on your data and search criteria - i.e. whether you expect this ID to be unique or not.

From your semantics it looks like you're doing a sort of repository like ID lookup, so my guess would be solution 2) and using Single or SingleOrDefault

The last choice is how you want your program to behave if nothing is found by ID

1. If you want an exception, use Single
2. If you want a null use SingleOrDefault

In Summary, all you have to do is change your last line of code to

return result.Single();

(And ofcourse, you don't need a call to ToList() just before that)

Cannot implicitly convert type [concrete] to [interface]

The accepted answer appears to be correct, but there are better ways to solve this problem. The preferred solution would be:

IEnumerable<IImportOrderLineModel> lines = 
  items.Where(x => x.OrderNumber == order.OrderNumber);
order.Lines = lines.ToList();

This solution eliminates two issues with the solution in Renat's answer:

• You start with a list and end with a list, so you'll need to create at least one new list. But FindAll creates another list, unnecessarily. That's extra work, extra collection pressure, and so on, in exchange for no benefit.
• The Cast<IImportOrderLineModel> operation similarly creates a new enumerator, but it is unnecessary; you can always simply do a covariant reference conversion for free to IEnumerable<IImportOrderLineModel>.

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