从属性获取值（如果不为空），否则通过Linq获取其他属性

Question

I have a Linq query with which i get data from an object like so:

var attachedItems = items.ToDictionary(
                               w => w.Number,
                               w => w.Attachments.Select(a => a.Name).ToArray()
                    );

This works fine so far, but sometimes the Attachments.Name property is empty. Then i'd like to get the value of another property.

To illustrate:

var attachedItems = items.ToDictionary(
                               w => w.Number,
                               w => w.Attachments.Select(a => a.Name).ToArray()
                               // If Attachments.Name == Empty, then get
                               w => w.EquipmentCode
                    );

How can i do this in a Linq query?

Answer 1

var attachedItems = items.ToDictionary(
       w => w.Number,
       w => w.Attachments.Select(a => a.Name)
                         .DefaultIfEmpty(w.EquipmentCode)
                         .ToArray()
                );

This retrieves all attachment names, if no attachments are there, an array with a single item containing the EquipmentCode value is returned.

If the EquipmentCode property is defined on the Attachment and you need it as fallback value for each attachment, then check Jon Skeet's answer.

Answer 2

Sounds like you just want the conditional operator:

var attachedItems = items.ToDictionary(
      w => w.Number,
      w => w.Attachments.Select(a => string.IsNullOrEmpty(a.Name) 
                                     ? a.EquipmentCode : a.Name)
                        .ToArray());

Answer 3

You could make your Select statement use a lambda and manually check the property like so:

var attachedItems = items.ToDictionary(
                               w => w.Number,
                               w => w.Attachments.Select(a => {
                                 if(String.IsNullOrEmpty(a.Name) == false) 
                                    return a.Name; 

                                  return a.EquipmentCode;
                              }).ToArray()
                     );