how to get rid of try/catch and improve the C# query?

Question

I have 2 list ModelA and ModelB and sample data like below,

 public class ModelA
{
    public string ModelAName { get; set; }
    public DateTime ModelATime { get; set; }
}


public class ModelB
{
    public string ModelBName { get; set; }
    public DateTime ModelBMinTime { get; set; }
    public DateTime ModelBMaxTime { get; set; }
}

Sample Data,

 var lstModelA = new List<ModelA>
        {
            new ModelA { ModelAName ="A1", ModelATime = new DateTime(2021, 04, 30)},
            new ModelA { ModelAName ="A2", ModelATime = new DateTime(2021, 04, 29)},
            new ModelA { ModelAName ="A6", ModelATime = new DateTime(2021, 03, 03)}
        };



        var lstModelB = new List<ModelB>
        {
            new ModelB { ModelBName ="A1", ModelBMinTime = new DateTime(2021, 01, 01), ModelBMaxTime = new DateTime(2021, 05, 05)},
            new ModelB { ModelBName ="A2", ModelBMinTime = new DateTime(2021, 01, 01), ModelBMaxTime = new DateTime(2021, 04, 29)},
            new ModelB { ModelBName ="A4", ModelBMinTime = new DateTime(2021, 04, 04), ModelBMaxTime = new DateTime(2021, 04, 05)}
        };    

I need to compare ModelB against ModelA where

• If ModelBName NOT exits in ModelAName , I want to return this record with same ModelBMinTime and ModelBMaxTime time. (example: A4 )

• If ModelBName = ModelAName and ModelATime = ModelBMaxTime , then I don't want to return this. (example 'A2')

   var a= lstModelA.First(x => x.ModelAName == "A2").ModelATime; var b = lstModelB.First(x => x.ModelBName == "A2").ModelBMaxTime;

  Here a=b!

• If ModelBName = ModelAName and ModelATime != ModelBMaxTime , then I want to return this result but ModelBMinTime should be replace with = ModelATime . (Example A1 )

I tried this, looping each ModelB and also try/catch since some ModelB (A4) nt present in lstModelA , how to get rid of it and improve this?

var data = new List<ModelB>();

        foreach (var modelB in lstModelB)
        {
            try
            {
                var modelA = lstModelA.First(x => x.ModelAName == modelB.ModelBName);

                if (modelA.ModelATime != modelB.ModelBMaxTime)
                {
                    data.Add(new ModelB { ModelBName = modelB.ModelBName, ModelBMinTime = modelA.ModelATime, ModelBMaxTime = modelB.ModelBMaxTime });
                }
            }
            catch (Exception)
            {
                data.Add(new ModelB { ModelBName = modelB.ModelBName, ModelBMinTime = modelB.ModelBMinTime, ModelBMaxTime = modelB.ModelBMaxTime });
            }

        }

Answer 1

Try using .FirstOrDefault() and check your variable for null afterwards:

var modelA = lstModelA.FirstOrDefault(x => x.ModelAName == modelB.ModelBName);

if (modelA == null)
{
    // not found / does not exist
}
else
{
    // found
}

Answer 2

You just need to make a null check instead of try-catch as far as I can see

var modelA = lstModelA.FirstOrDefault(x => x.ModelAName == modelB.ModelBName);

if (modelA != null && modelA.ModelATime != modelB.ModelBMaxTime)
{
    data.Add(new ModelB 
             { 
                 ModelBName = modelB.ModelBName, 
                 ModelBMinTime = modelA.ModelATime, 
                 ModelBMaxTime = modelB.ModelBMaxTime 
             });
}
else if (modelA == null)
{
    data.Add(new ModelB 
             { 
                 ModelBName = modelB.ModelBName, 
                 ModelBMinTime = modelB.ModelBMinTime, 
                 ModelBMaxTime = modelB.ModelBMaxTime 
             });
} 

however, if modelB might be null you need to check that also.

Answer 3

What about a join, assuming you aren't dealing with static lists and they grow to larger sizes a join should give you better performance.

var data =
    (from mb in lstModelB
    join ma in lstModelA on
    mb.ModelBName equals ma.ModelAName
    into gj
    from sma in gj.DefaultIfEmpty()
    where sma is null || sma.ModelATime != mb.ModelBMaxTime
    select new ModelB
    {
        ModelBName = mb.ModelBName,
        ModelBMinTime = sma?.ModelATime ?? mb.ModelBMinTime,
        ModelBMaxTime = mb.ModelBMaxTime
    })
    .ToList();