LINQ new instance when SingleOrDefault returns null

Question

I have this simple method:

    #region Fields

    private Collection<Address> _addresses;

    #endregion

    #region Public methods

    public Address DeliveryAddress()
    {
        if (_addresses == null)
            if (this.Id > 0)
                _addresses = Core.Data.Addresses.GetClient(this.Id);

        return _addresses.SingleOrDefault(x => x.TypeId == AddressType.Delivery);
    }

    public Address InvoiceAddress()
    {
        if (_addresses == null)
            if (this.Id > 0)
                _addresses = Core.Data.Addresses.GetClient(this.Id);

        return _addresses.SingleOrDefault(x => x.TypeId == AddressType.Invoice);
    }

    #endregion

As you can see I trying to return one result for a DeliveryAddress and one result for an InvoiceAddress. My problem is that I would like the link expression to create a new instance of Address() if SingleOrDefault returns null. I am really new to linq, so I am not sure whether SingleOrDefault is the correct expression I should be using.

Answer 1

You could use DefaultIfEmpty and use that instance as default value:

return _addresses.Where(x => x.TypeId == AddressType.Delivery)
                 .DefaultIfEmpty(new Adress())
                 .Single();

Answer 2

Use the null-coalescing operator:

return _addresses
    .SingleOrDefault(x => x.TypeId == AddressType.Delivery) ?? new Address();

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The expression

x ?? y

yields x if x is not null, otherwise y. You can chain the operator

x ?? y ?? z ?? t

This returns the first non-null value or null if all of them are null.

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UPDATE

Note that SingleOrDefault throws an exception if the sequence has more than one element. If you need the first element of a sequence possibly having no or more than one element, use FirstOrDefault instead.