装订清单 <string> 从模型到视图模型

Question

I am trying to bind List from model to viewModel

Here is my model:

public class Instruction
{
    public int ID { get; set; }
    public List<string> Target { get; set; }
    public bool Delete { get; set; }
    public List<string> DeleteLines { get; set; }
    public string SpecificLine { get; set; }
    public Insert InsertType { get; set; }
    public string Insert { get; set; }
    public MigrationPart? Part { get; set; }
}

The view model is identical. I am trying to to bind it like this:

        var instructions = myDbContext.Instructions;
        var model = instructions.Select(i => new InstructionView
        {
            Target = i.Target,
            Delete = i.Delete,
            DeleteLines = i.DeleteLines,
            SpecificLine = i.SpecificLine,
            InsertType = i.InsertType,
            Insert = i.Insert,
            Part = i.Part
        });

        return View("MigrationsList", model);

However, when I try to display it I get the error:

The specified type member 'Target' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported

What is the right approach to this?

Answer 1

Materialize the query first:

var instructions = myDbContext.Instructions.ToList();

ToList actually brings all your database records into memory. After that, you are making the mapping between the Entity and ViewModel.

If you do not add ToList , the Select is actually trying to be translated into SQL. Since a SQL query generated by Entity Framework cannot get a list if integers and map it into your class, that exception is thrown.