带有日期范围的LINQ查询

Question

in my DB i have the following table:

name, date_start, date_end, value
test1, 01.01.2019, 05.01.2019, 10
test2, 03.01.2019, 06.01.2019, 11

Now i want to select the rows as the following result:

name, date, value
test1, 01.01.2019, 10
test1, 02.01.2019, 10
test1, 03.01.2019, 10
test1, 04.01.2019, 10
test1, 05.01.2019, 10
test2, 03.01.2019, 11
test2, 04.01.2019, 11
test2, 05.01.2019, 11
test2, 06.01.2019, 11

The result must be for every day, one entry with the same values. Could anyone help me?

Tanks

Answer 1

This wouldn't really be a DB operation, but probably best served in memory.

var records = context.data.ToList(); // Add Where clause for boundary..

var byDate = records.SelectMany(x => Enumerable.Range(0, 1 + (int)x.date_end.Subtract(x.date_start).TotalDays)
    .Select(d => new { x.Name, Date = x.date_start.AddDays(d), x.Value })).ToList();

The caveat is that the byDate run needs to be done against memory. The first query would be to retrieve the appropriate records containing the date ranges. This gets materialized by the ToList() call. From there we can select a range of dates using Enumerable.Range and compose those with the record Name and Value figures to get an object containing the fields from the record with each applicable date in the range. This example uses an anonymous type for the result, but you can easily substitute that with a view model.

Answer 2

a different approach on @StevePy 's answer, it will still be executed on memory.

public class ReturnClass
{
    public string name {get; set;}
    public DatTime date {get; set;}
    public string/int value {get; set;}
}

var records = context.data.ToList();

var results = new List<ReturnClass>();

foreach(var record in records)
{
    var date = record.date_start;
    while(date <= record.date_end)
    {
        results.Add(new ReturnClass
        {
            name = record.name,
            date = date,
            value = record.value
        }
        date = date.AddMonths(1);
    }
}

return results;