Convert if else statement to simple linq query-CodePudding

I have been trying to convert a simple if else to a linq statement.

The if else statement goes something like this:

if ( MessageStatus = 1 )
   then MessageCount > 0
else if ( MessageStatus = 2 )
   then MessageCount = 0
else
   do nothing

This is what I have in my linq so far and it didn't query out the data I wanted

var query = _context.Message
                    .Where(c => request.MessageStatus.Equal(2) ? c.MessageCount.Equals(0) :
                                   request.MessageStatus.Equal(1) ? c.MessageCount > 0 :
                                      request.MessageStatus.Equal(0));

It should be able to return rows of data but instead it return nothing.

Where does the problems lie at?

Thanks

CodePudding user response：

What you're asking about is conditional filtering. request.MessageStatus is a value you know before you execute the query, so you can use it to define which Where to add to the query.

This works by creating a IQueryable<...> for the whole data set (your table), then adding on the Where that you want based on some condition. It's important to note that you're always doing query = query.Where(...);, if you don't re-assign query you lose the additional filter.

// "request" is defined earlier
IQueryable<Message> query = _context.Message; // might need .AsQueryable() here

if (request.MessageStatus == 1)
{
    query = query.Where(r => r.MessageCount > 0);
}
else if (request.MessageStatus == 2)
{
    query = query.Where(r => r.MessageCount = 0);
}
else
{
    // assuming that this means "include all records",
    // don't perform any additional filtering
    // you don't need this "else"
}

List<Message> results = query.ToList();

It's also good to know that this pattern works outside of EF as well with basic IEnumerables and in memory collections.