how to filter records and get first record based on date using c#-CodePudding

I am writing a Unit test where in i am passing array of two records and i want to send it to a method which can filter the records and pass only a single record but i have tried to use FirstOrDefault but then it is throwing compile time error

here is my code

[Test]
        public void Test()
        {
            var first = new Extra
            {
                Code = "P1",
                Cost= 100,
                DateFrom = DateTime.Parse("01 March 2022")
            };
            var second = new Extra
            {
                Code = "P3",
                Cost= 120,
                DateFrom = DateTime.Parse("01 April 2022")
            };
            var totalData= new[]
            {
                first,
                second
            };


            var value= GetExtraHandler.FetchExtras(totalData, DateTime.Parse("02 April 2022"));

            Assert.Equal(value, new[] { second });

Here is method which get called in GetExtraHandler

    public static IEnumerable<Extra> FetchExtras(Extra[] lvl, DateTime idate)
    {

        var data= lvl.Where(x => x.DateFrom < idate).FirstOrDefault();
        return data;
    }

So from this code when i build i am getting compile time error that method expects IEnumerable return type so if i use firstordefault it is throwing error. I want a way so that if multiple records is less than datefrom i.e 02 April 2022 and in array which is passed is 01 April and 01 March then only 01 April record should get fetched. Thanks for help in advance.

CodePudding user response：

you have to fix FetchExtras method

public static IEnumerable<Extra> FetchExtras(Extra[] lvl, DateTime idate)
{
return lvl.Where(x => x.DateFrom < idate).OrderByDescending(x=> x.DateFrom).Take(1);
}

result

[
  {
    "Code": "P3",
    "Cost": 120,
    "DateFrom": "2022-04-01T00:00:00"
  }
]

CodePudding user response：

You could yield return the item containing the latest DateFrom amongst those items that fulfill your condition:

public static IEnumerable<Extra> FetchExtras(Extra[] lvl, DateTime idate)
{
    yield return lvl.Where(x => x.DateFrom < idate).MaxBy(x => x.DateFrom);
}

.MaxBy() is available from .Net 6.
MaxBy( * ) can be replaced with e.g. .OrderByDescending( * ).First().