Question

I can not understand the following line: x => x.Id == _purchase.Centre.Id

the code is here:

private void LoadCentreOptions()
{
    MaterialCentreDataSource mcds = new MaterialCentreDataSource();
    List<MaterialCentre> centres = mcds.GetAll() as List<MaterialCentre>;

    _blankCentre = new MaterialCentre()
    {
        Name = Strings.JournalViewModel_CreditedPartyOption_NotSpecified
    };

    centres.Insert(0, _blankCentre);
    _centreOptions = new ReadOnlyCollection<MaterialCentre>(centres);

    if (_purchase.Centre == null)
        _purchase.Centre = _blankCentre;
    else
        _purchase.Centre = _centreOptions.First(x => x.Id == _purchase.Centre.Id);
}

here at the debugging time i am watching that X.Id is incremented .How it is possible?

Answer 1

The api First is enumerating over the collection and applying the condition to check which one matches and then returns the first match.. So effectively the code translates to

foreach(var centreOption in _centreOptions)
{
    if(centreOption.Id==_purchase.Centre.Id)
        return centreOption;
}

and if you understand LINQ its basically short for

_centreOptions.Where(x => x.Id == _purchase.Centre.Id).First();

To understand the exact implementation of First read Jon Skeets blogpost.