Question

I am trying to remove elements from an IEnumerable type from another IEnumerable.

Here I get the complete list

var tiposObj = from t in context.sistema_DocType
                               select
                                   new tgpwebged.Models.SettingsModels.TipoIndiceModel
                                   {
                                       id = t.id,
                                       tipo = t.tipoName
                                   };

                classificacaoModel.tipos = tiposObj.ToList();

And here a partial list to be excluded from the first

  var tiposAtribuidosObj = from t in context.sistema_DocType
                                        join c in context.sistema_ClassificacaoTipo on t.id equals c.idTipo
                                        where c.idClassificacao == classificacaoId
                                        select new tgpwebged.Models.SettingsModels.TipoIndiceModel
                                        {
                                            id = t.id,
                                            tipo = t.tipoName
                                        };
                classificacaoModel.tiposAtribuidos = tiposAtribuidosObj.ToList();   

Here is how I am excluding:

classificacaoModel.tiposNaoAtribuidos = classificacaoModel.tipos.Except(classificacaoModel.tiposAtribuidos);

No elements is excluded from the first list. Can´t figure out why. They have same structure and same types.

Answer 1

.NET framework has no way to compare 2 instances of TipoIndiceModel.
For this you have to implement IEqualityComparer or derive from EqualityComparer.

Hint from MSDN on Except:

This interface supports only equality comparisons. Customization of
comparisons for sorting and ordering is provided by the IComparer
generic interface.

We recommend that you derive from the EqualityComparer class
instead of implementing the IEqualityComparer interface, because
the EqualityComparer class tests for equality using the
IEquatable.Equals method instead of the Object.Equals method. This
is consistent with the Contains, IndexOf, LastIndexOf, and Remove
methods of the Dictionary class and other generic
collections.