linq/EF/lambda Group by/Order by 多个字段详细用法

1）单个字段Group by：

//a.Key类型与a.Province字段类型一样
.GroupBy(a => a.Province).Select(a => a.Key).ToList();

2）多个字段Group by：

//此时返回的数据列表需要自己转换
.GroupBy(a => new { a.Date, a.Week }).Select(a => a.Key).ToList();

3）单个字段Order by：

.OrderBy(a => a.Date).ToList()

4）多个字段Order by：

.OrderBy(a => a.Date).ThenBy(a => a.EndTime).ThenBy(a => a.StartTime).ToList()

5）多个字段Order by倒序：

.OrderByDescending(a => a.Date).ThenByDescending(a => a.EndTime).ThenByDescending(a => a.StartTime).ToList()

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GroupBy根据多个字段 分组使用方式：

一、使用扩展方法

query.GroupBy(q => new { q.Year, q.Month })
.Select(q => new
{
Year = q.Key.Year,
Month = q.Key.Month,
BuildAmount = q.Sum(i => i.BuildAmount),
RecAmount = q.Sum(i => i.RecAmount),
Amount = q.Sum(i => i.Amount),
RealAmount = q.Sum(i => i.RealAmount)
});

二、Linq方式
var query = from l in list
group l by new { l.Name, l.BatNum } into g
select new
{
Name = g.Key.Name,
Count = g.Sum(a => a.Count),
BatNum = g.Key.BatNum
};
三、生成KeyValue类型

Dictionary<string,decimal> buildList = _build.FindList().GroupBy(q => q.SaleCode)
.Select(q => new { Code = q.Key, ReaAmount = q.Sum(i => i.RealAmount) })
.ToDictionary(q => q.Code, q => q.ReaAmount);
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