关于c＃：如何使用linq按月查询计数和分组

How to write a count and group by month query with linq

这是我在ASP.NET核心中使用Entity Framework核心的第一个C应用程序，我正在尝试在Linq中编写以下MySQL查询：

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SELECT districtid, COUNT(id), MONTH(registerDate)
FROM StreetCrimes
GROUP BY districtid, MONTH(registerDate)

我面临的问题是编写LINQ代码。为了接近答案，我尝试了以下方法：

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var StreetCrimes = this.database.StreetCrimes
.Select(s => s.district)
.Count(s => s.id > 0)
.GroupBy(s => s.district)
.ThenBy(s => s.registerDate);

如果能帮上忙，我们将不胜感激。

我的StreetCrime班：

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public class StreetCrime
{
public int id { get; set; }

public string caseNumber { get; set; }
public District district { get; set; }
public DateTime registerDate { get; set; }
public TimeSpan crimeTime { get; set; }
}

相关讨论

地区需要继承IEqualityComparer，GroupBy才能工作。LINQ应该如下所示：

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var StreetCrimes = this.database.StreetCrimes
.Where(x => x.id > 0)
.GroupBy(s => new {district = s.district, date = s.registerDate})
.Select(x => new { count = x.Count(), district = x.Key.district, date = x.Key.date})
.ToList();

这应该有效：

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var StreetCrimes = this.database.StreetCrimes
.Where(x => x.id > 0)
.GroupBy(s => new {district = s.district, month = s.registerDate.Month})
.Select(x => new { count = x.Count(), district = x.Key.district, month = x.Key.month})
.ToList();

多亏了@jdweng，我才更接近答案。不过，我每个月都需要这笔钱。

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var StreetCrimes = this.database.StreetCrimes
.Where(x => x.id > 0)
.GroupBy(s => new {district = s.district, date = s.registerDate.Month})
.Select(x => new { count = x.Count(), district = x.Key.district, date = x.Key.date})
.ToList();

你可以和林肯一起去

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但是你也可以用一个DataTable。

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SqlCommand cmd = new SqlCommand("SELECT districtid,COUNT(id),MONTH(registerDate) FROM StreetCrimes GROUP BY districtid,MONTH(registerDate)",connectionString)

DataTable dt = new DataTable();
SqlDataAdapter ada = new SqlDataAdapter(cmd);
ada.Fill(dt)
int crimeCount = dt.Rows.Count();

或者两行行可以：

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SqlCommand cmd = new SqlCommand("SELECT districtid, COUNT(id),MONTH(registerDate) FROM StreetCrimes GROUP BY districtid,MONTH(registerDate)",connectionString)

int crimeCount = CInt(cmd.ExecuteScalar());