Question

这是我在ASP.NET Core中使用Entity Framework Core的第一个C＃应用程序，我尝试在Linq中编写以下MySQL查询：

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。我已尝试以下方法来接近答案：

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

任何帮助实现这一目标的人都将不胜感激。

我的StreetCrime课程：

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; }
}

Answer 1

District需要继承IEqualityComparer才能使GroupBy正常工作。 linq应该是这样的：

       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();

Answer 2

你可以使用LINQ

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_select);

    mspin=(Spinner) findViewById(R.id.spinner1);
    submit = (Button) findViewById(R.id.btn1);
    layout = (LinearLayout) findViewById(R.id.linear);
    lay = (LinearLayout) findViewById(R.id.li);
    edt=(EditText) findViewById(R.id.ed2);
    sc = (ScrollView) findViewById(R.id.sc1);

    int no = 20;
    allEds = new ArrayList<EditText>();
    for (int i=1;i<=no;i++){
        LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.WRAP_CONTENT);
        edtAdd = new EditText(SelectActivity.this);

        layout.setLayoutParams(params);
        allEds.add(edtAdd);
        edtAdd.setHint("Enter Name" + i);
        edtAdd.setId(i);
        layout.addView(edtAdd);
    }
    submit.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if (allEds.size()<=9) {
                Intent data = new Intent(SelectActivity.this, HalfPieChartActivity.class);
                String[] items = new String[allEds.size()];
                String str = String.valueOf(allEds.size());
                data.putExtra("size", str);  //you don't need to keep this in loop as its same.
                data.putExtra("edt", edt.getText().toString());
                for (int j = 0; j < allEds.size(); j++) {
                    items[j] = allEds.get(j).getText().toString();
                    data.putExtra("edData" + j, items[j]);
                }

                startActivity(data);
            }
            else {
                Intent data = new Intent(SelectActivity.this, FullPieChartActivity.class);
                String[] items = new String[allEds.size()];
                String str = String.valueOf(allEds.size());
                data.putExtra("size", str);// this is the line where I sent that count
                data.putExtra("edt", edt.getText().toString());
                for (int j = 0; j < allEds.size(); j++) {
                    items[j] = allEds.get(j).getText().toString();
                    data.putExtra("edData" + j, items[j]);//here is filled data send line
                }

                startActivity(data);
            }
        }
    });

}
}

但您也可以使用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();。

DataTable

或者可能有两行：

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();

Answer 3

感谢@jdweng，我更接近我的回答。但是我需要每个月的总金额。

        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();

Answer 4

这应该有效：

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();

如何使用linq按月查询计数和分组

4 个答案: