CODEWITHSUNDEEP
c#linqselectprojection
ewahner
ewahner

Reputation: 1189

How do you create a dynamic select projection from a generic using Linq in C#?

So I have a function that I pass Func call back to. I would also like to add some sort of selection projection to be able to do the projection on the object, meaning I would only perform one database call. The function looks something like this:

public T Get<T>(string id, Func<T> getItemCallback) where T : class
{
    item = getItemCallback();
    if (item != null)
    {
        doSomeThing(item);
        // Here I would like to call something else that is 
        // expecting a specific type.  Is there way to pass in a
        // dynamic selector?
        doSomethingElse(item.Select(x => new CustomType { id = x.id, name = x.name }).ToList());
    }
    return item;
}

void doSomethingElse(List<CustomType> custom)
{
    ....
}

Leme show how I cam currently calling this perhaps that will help:

public List<MyDataSet> GetData(string keywords, string id)
{
    return _myObject.Get(
       id, 
       () => db.GetDataSet(keywords, id).ToList());
    // Perhaps I could add another parameter here to 
    // handled the projection ????
}

Thanks to Reed I figured it out...would look like this:

public T Get<T>(string id, Func<T> getItemCallback, Func<T, List<CustomType>> selector) where T : class
{
     item = getItemCallback();
     if (item != null)
     {
          doSomething(item);
          var custom = selector(item);
          if (custom != null)
          {
              doSomethingElse(custom);
          }
     }
     return item;
 }

And The call looks like:

 public List<MyDataSet> GetData(string keywords, string id)
 {
     return _myObject.Get(
         id,
         () => db.GetDataSet(keywords, id).ToList(),
         x => x.Select(d => new CustomType { id = d.ReferenceId, name = d.Name })
               .ToList());
 }

Upvotes: 1

Views: 1169

Answers (1)

Reed Copsey
Reed Copsey

Reputation: 564691

You would need to also pass in a conversion function:

public T Get<T>(string id, Func<T> getItemCallback, Func<T, List<CustomType>> conversion) where T : class
{
    item = getItemCallback();
    if (item != null)
    {
        doSomeThing(item);

        if (conversion != null)
            doSomethingElse(conversion(item));
    }
    return item;
}

Upvotes: 2

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