基于日期实体框架和LINQ的数据分组

Question

I have a array of analytic events in my database and i would like to send this data grouped by date to my client app.

The data from the db looks something like this (but with hundreds of records):

[
  {
    "DateAdded": "2006-12-30 00:38:54",
    "Event": "click",
    "Category": "externalWebsite"
  },
  {
    "DateAdded": "2006-07-20 00:36:44",
    "Event": "click",
    "Category": "social"
  },
  {
    "DateAdded": "2006-09-20 00:36:44",
    "Event": "click",
    "Category": "social"
  },
  {
    "DateAdded": "2006-09-22 00:12:34",
    "Event": "load",
    "Category": "profile"
  }
]

What I would like to do is return the count of all the say 'social' 'click' but by month so it would look like this:

[
  {
    "name": "socialclicks",
    "series": [
      {
        "count": 259,
        "name": "Jan"
      },
      {
        "count": 0,
        "name": "Feb"
      },
      {
        "count": 52,
        "name": "Mar"
      }
      ... etc, etc up to Dec <====
    ]
  }
]

So, what I have been trying is to get all the records that are associated with a particular user using their id. This is simple.

Now I need to split them records into monthly counts showing the last 12 months from the current month (if the month doesn't exist return 0) - this is proving to be complicated and difficult.

My approach was this:

var records = context.records.where(r => r.Id = userId).ToList();
var jan
var feb
var mar
var apr
... etc, etc

for (int i = 0; i < records.Count ; i++)
{
    if (record.DateAdded > "2005-12-31 00:00.00" && record.DateAdded < "2006-01-31 00:00.00") {
       jan++;
    }

    if (record.DateAdded > "2006-01-31 00:00.00" && record.DateAdded < "2006-02-28 00:00.00") {
       feb++;
    }

    ...etc, etc
}

Then i use these variables to count and hard code the name for the returned data.

As you can see, there is lots of etc, etc because the code has become ridiculous!

There must be a more simple way to do this but i cant seem to find one!

Any assistance would be appreciated.

Thanks

Answer 1

The first thing to do is group all your data by the 2 properties you're interested in

• Event
• Category

Example:

 var partialResult = entries.GroupBy(x => new {
       x.Event,
       x.Category
    });

From there, when you project your result and you can group again by Month & Year. - anonymous object used for demo, but you could easily define this as a struct/class as appropriate:

var result = entries.GroupBy(x => new {
       x.Event,
       x.Category
    }).Select(g => new {
       g.Key.Event,
       g.Key.Category,
       Series = g.GroupBy(x => new {x.DateAdded.Month, x.DateAdded.Year})
                 .Select(i => new{
                         i.Key.Month,
                         i.Key.Year,
                         Count = i.Count()
                }).ToArray()
    });

foreach(var item in result)
{
    Console.WriteLine($"Event:{item.Event} Category:{item.Category}");
    foreach(var serie in item.Series)
        Console.WriteLine($"\t{CultureInfo.CurrentCulture.DateTimeFormat.GetMonthName(serie.Month)}{serie.Year} Count={serie.Count}");
}

---

Edit: To satisfy your requirement that:

if the month doesn't exist return 0

You need to add a few complexities. First a method which can work out all the Month/Year combinations between 2 dates.

private static IEnumerable<(int Month, int Year)> MonthsBetween(
        DateTime startDate,
        DateTime endDate)
{
    DateTime iterator;
    DateTime limit;

    if (endDate > startDate)
    {
        iterator = new DateTime(startDate.Year, startDate.Month, 1);
        limit = endDate;
    }
    else
    {
        iterator = new DateTime(endDate.Year, endDate.Month, 1);
        limit = startDate;
    }

    var dateTimeFormat = CultureInfo.CurrentCulture.DateTimeFormat;
    while (iterator < limit)
    {
        yield return (iterator.Month,iterator.Year);                
        iterator = iterator.AddMonths(1);
    }
}

Also you'll need some kind of range to both calculate all the months between, as well as filter your original query:

var dateRangeStart = DateTime.Parse("2006-01-01");
var dateRangeEnd = DateTime.Parse("2007-01-01");
var monthRange = MonthsBetween(dateRangeStart,dateRangeEnd);

var results = entries.Where(e => e.DateAdded>=dateRangeStart && e.DateAdded<dateRangeEnd)
     ..... etc

And then, when outputting results you need to effectively do a left join onto your list of years/months. For some reason this is easier using query syntax than lambda.

foreach(var item in results)
{
    Console.WriteLine($"Event:{item.Event} Category:{item.Category}");

    var joinedSeries = from month in monthRange
                        join serie in item.Series
                        on new{month.Year, month.Month} equals new {serie.Year, serie.Month} into joined
                        from data in joined.DefaultIfEmpty()
                        select new {
                            Month = data == null ? month.Month : data.Month,
                            Year = data == null ? month.Year : data.Year,
                            Count = data == null ? 0 : data.Count
                        };


foreach(var serie in joinedSeries)
    Console.WriteLine($"\t{CultureInfo.CurrentCulture.DateTimeFormat.GetMonthName(serie.Month)}{serie.Year} Count={serie.Count}");
}

Live example: https://dotnetfiddle.net/K7ZoJN