通常将IQueryable列表转换为dto对象的列表

Question

Background

I have an extension method that converts a list of IQueryable<> to an IEnumerable<>:

public static IEnumerable<PersonDto> ToDtoList(
    this IQueryable<Person> source)
{
    var result = new List<PersonDto>();

    foreach (var item in source)
    {
        result.Add(item.ToDto());
    }

    return result;
}

The item.ToDto extension does this:

public static PersonDto ToDto(this Person source)
{
    if (source == null)
        return null;

    return new PersonDto
    {
        PersonId = source.personId,
        Firstname = source.firstname,
        Lastname = source.lastname,
        DateOfBirth = source.dateOfBirth,
        CreateDate = source.createDate,
        ModifyDate = source.modifyDate,
    };
}

The question

Is there a way to configure the following so that item.ToDto() works?

public static IEnumerable<T2> ToDtoList<T, T2>(this IQueryable<T> source)
{
    var result = new List<T2>();

    foreach (var item in source)
    {
        result.Add(item.ToDto());
    }

    return result;
}

As is, it doesn't work because .ToDto is an unresolvable symbol for item .

Answer 1

The problem (as you may know) is how to "generically" map a T to a T2 ?

You can either use a tool like AutoMapper that you can configure to map generically between any two types, or you can add a parameter for a mapping function:

public static IEnumerable<T2> ToDtoList<T, T2>(this IQueryable<T> source, Func<T, T2> map)
{
    var result = source.AsEnumerable()  // to avoid projecting the map into the query
                       .Select(s => map(s));

    return result;
}