linq to sql distinct

转载于 2018-08-10 18:59:45 发布 · 903 阅读

本文介绍了如何使用 LINQ 的 Distinct 方法对数据进行去重处理，包括单列和多列的去重操作，并提供了实现自定义类去重的示例代码。

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单列：
MyDataContext db = new MyDataContext();
var result = (from p in db.t_Personnel
                  select p.FirstName).Distinct();
DataTable dt = new DataTable("SingleDistinct");
dt.Columns.Add("FirstName");
foreach (var item in result)
{
    DataRow dr = dt.NewRow();
    dr["FirstName"] = item.ToString();
    dt.Rows.Add(dr);
}
dataGridView1.DataSource = dt;

多列：
using System.Data;
using System.Collections;
namespace Test_Distinct
{
    public class PersonDataRowComparer : IEqualityComparer<t_Personnel>
    {
        public bool Equals(t_Personnel t1, t_Personnel t2)
        {
            return (t1.ID == t2.ID && t1.FirstName == t2.FirstName);
        }
        public int GetHashCode(t_Personnel t)
        {
            return t.ToString().GetHashCode();
        }
    }
}

MyDataContext db = new MyDataContext();
IEnumerable distinctRows = db.t_Personnel.ToList().Distinct(new PersonDataRowComparer());
DataTable dt = new DataTable("SingleDistinct");
dt.Columns.Add("ID");
dt.Columns.Add("FirstName");
dt.Columns.Add("LastName");
foreach (var item in distinctRows)
{
    DataRow dr = dt.NewRow();
    dr["ID"] = item.ID;
    dr["FirstName"] = item.FirstName;
    dr["LastName"] = item.LastName;
    dt.Rows.Add(dr);
}
dataGridView1.DataSource = dt;

如果是对于自定义类，此处要注意：

public class PersonDataRowComparer : IEqualityComparer <类名>

http://msdn.microsoft.com/en-us/library/bb338049.aspx

from:https://blog.youkuaiyun.com/q107770540/article/details/5784646

///////////////////////////////////////////////////

linq 集合按照多列进行distinct

List<TaskBatch> sourceList = (from c in BatchCollecion
  group c by new
      {
          c.CustomId,
          c.OutsourcingDate,
          c.ServiceId
      } into grp
  select grp.First()).ToList();

或者

List<TaskBatch> sourceList = BatchCollecion.GroupBy(x => new { x.CustomId, x.ServiceId, x.OutsourcingDate }).Select(x => x.First()).ToList();

from:https://blog.youkuaiyun.com/swarb/article/details/19170133