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Convert if-else within a foreach loop to LINQ

What I am trying to achieve is converting this foreach loop to a LINQ equivalent. The current code loops through a list of generic objects IE List which are DB objects and then creates local objects based off of the object Type.

foreach (var message in messages)

if (message is TextMessageData)

output.Add(new TextMessage

Content = ((TextMessageData)message).Content,
Sender = ((TextMessageData)message).Sender,
TimeSent = ((TextMessageData)message).TimeSent
);

else if(message is ImageDataRecord)

output.Add(new ImageMessage

ImageUrl = ((ImageDataRecord)message).Url,
Sender = ((ImageDataRecord)message).Sender,
TimeSent = ((ImageDataRecord)message).TimeSent
);




Thus far my code looks like this, however, I am unsure of how to return a result set for each if statement condition

var data = from message in messages
where message is TextMessageData
select new TextMessage

Content = ((TextMessageData)message).Content,
Sender = ((TextMessageData)message).Sender,
TimeSent = ((TextMessageData)message).TimeSent
;


1 Answer
1

How about something along these lines:

var textMessages = messages.OfType<TextMessageData>().Select(m => (Message)new TextMessage() … );
var imageMessages = messages.OfType<ImageDataRecord>().Select(m => (Message)new ImageMessage() … );
var output = textMessages.Concat(imageMessages).ToList();


In a single line, this would look like this:

var output = messages.OfType<TextMessageData>()
.Select(m => (Message)new TextMessage() … )
.Concat(messages.OfType<ImageDataRecord>()
.Select(m => new ImageMessage() … ))
.ToList();


Another solution is to "cheat" a bit and put the whole if-statement into a lambda, like this:

var output = messages.Where(message => message is TextMessageData || message is ImageDataRecord)
.Select(message =>

if (message is TextMessageData)

return (Message)new TextMessage

…
;

else if (message is ImageDataRecord)

return new ImageMessage

…
;

else
throw new Exception();
).ToList();


Calling .ToList() at the end of the LINQ statement to create an actual List<T> makes only sense if you have enough memory to keep all elements in memory AND if you access the elements multiple times.

.ToList()

List<T>

There are many other ways to reduce the amount code. For example, you might consider pattern matching, deconstructing, or the yield keyword:

yield

IEnumerable<Message> ConvertMessages()

foreach (var message in messages)
if(message is TextMessageData tmd)
yield return new TextMessage()

ImageUrl = tmd.Url,
Sender = tmd.Sender,
TimeSent = tmd.TimeSent

else if (message is ImageDataRecord ird)
yield return new ImageMessage()

ImageUrl = ird.Url,
Sender = ird.Sender,
TimeSent = ird.TimeSent




A much more important question is whether you have to do the conversion in the first place. Converting objects from one type to another type has little value by itself. It wastes time and memory.

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