how to convert list to IEnumerable?

Question

I have the following function in which should return an IEnumerable type?how do I convert list to IEnumerable? and return an empty IEnumerable?

public IEnumerable<SoftwareImageTestPlan> GetAssignedTestPlansForSPSI(int SoftwareProductID, int SoftwareImageID)
{
    var records = _entities.tblSoftwareImageTestPlans
        .Where(x => x.SoftwareProductID == SoftwareProductID && x.SoftwareImageID == SoftwareImageID)
        .ToList();

    if (records == null)
        return new List<SoftwareImageTestPlan>();
    else
        return records;
}

Error:

Cannot implicty convert type 'System.Collections.Generic.List<....> to System.Collections.Generic.IEnumerable<.....>.An explicit conversion exists(are you missing a cast?)

Answer 1

Problem is not in convertation of List<T> to IEnumerable<T>. Becuase List<T> implements IEnumerable<T>.

Your problem is that generic parameters are different. You are trying to convert List<T1> to IEnumerable<T2>. Where:

• T1 is QlasrService.EntityFramework.tblSoftwareImageTestPlan
• T2 is QlasrService.Model.SchemaModels.LAP.SoftwareImageTestPlan

Simplest solution will be mapping (either manual or automatic). Automatic mapping is very easy. Add Automapper nuget package. Place this line somewhere on application start:

Mapper.Initialize(cfg => cfg.CreateMap<tblSoftwareImageTestPlan, SoftwareImageTestPlan>());

And now your method will look like:

public IEnumerable<SoftwareImageTestPlan> GetAssignedTestPlansForSPSI(
   int SoftwareProductID, int SoftwareImageID)
{
    var testPlans = from tp in _entities.tblSoftwareImageTestPlans
                    where tp.SoftwareProductID == SoftwareProductID && tp.SoftwareImageID == SoftwareImageID
                    select tp;

    return Mapper.Map<IEnumerable<SoftwareImageTestPlan>>(testPlans);
}

NOTE: In your code either records cannot have null value, or you will have NullReferenceException at ToList() call. So if..else block is useless anyway.

Answer 2

You're returning two different object types:

• tblSoftwareImageTestPlan - Which resides in your Entity Framework model
• SoftwareImageTestPlan - Which resides in your Qlasr Schema Models

Therefore when you state the following:

return records;

It will complain that the records object is not of type SoftwareImageTestPlan. Therefore you need to convert records into a new List<SoftwareImageTestPlan> which you can achieve via a LINQ projection.

var records = (from entities in _entities.tblSoftwareImageTestPlans
               where entities.SoftwareProductID equals SoftwareProductID && entities.SoftwareImageID == SoftwareImageId
               select new SoftwareImageTestPlan
               {
                  SoftwareProductID = entities.SoftwareProductID,
                  SoftwareImageID = entities.SoftwareImageID
               }).ToList();

You can then use your original statement:

if (records == null)
    return new List<SoftwareImageTestPlan>();
else
    return records;

Answer 3

The problem here isn't that you need to convert from List to IEnumerable.

The problem is that you're trying to convert from List<tblSoftwareImageTestPlan> to IEnumerable<SoftwareImageTestPlan>

Those are two completely different types, because of the type argument.

Possible solutions:

• Change the return type to IEnumerable<tblSoftwareImageTestPlan>

• Map the objects to SoftwareImageTestPlan by projecting the tblSoftwareImageTestPlan to a SoftwareImageTestPlan:

  public IEnumerable<SoftwareImageTestPlan> GetAssignedTestPlansForSPSI(int softwareProductID, int SoftwareImageID)
  {
      var records = _entities.tblSoftwareImageTestPlans
                             .Where(x => 
                               x.SoftwareProductID == SoftwareProductID && 
                               x.SoftwareImageID == SoftwareImageID)
                             .Select(x => new SoftwareTestPlan { 
                               Id = Id,  // example
                               ... do more mapping here  
                              })
                             .ToList();
  
      if (records == null)
          return new List<SoftwareImageTestPlan>();
      else
          return records;
  }