Question

我有以下查询可以正常工作。但是，它不适用于需要它的连接查询。

var ra = from c in _context.Wxlogs
         select c;

if (year == "2011")
{
    ra = (IQueryable<Wxlog>)(from c in _context.Wxlogs
                             where c.LogYear == year 
                                   && (SqlFunctions.DatePart("Month", c.LogDate2) == m3) 
                                   && c.LogTime.Contains("23:59")
                             orderby c.LogDate2
                             let LogDate = c.LogDate2
                             select new { 
                                 LogDate, 
                                 c.Rain_today 
                             });
}
else if (year != "2011")
{
    ra = (IQueryable<Wxlog>)(from c in _context.Wxlogs
                             where c.LogYear == year 
                             && c.LogMonth == mm 
                             && c.LogTime.Contains("08:59")
                             orderby c.LogDate2
                             let LogDate = EntityFunctions.AddDays(c.LogDate2, -1)
                             select new { 
                                 LogDate, 
                                 c.Rain_today 
                             });
}

因此，我一直试图在条件（something like this answer by Whaheed）没有运气的情况下嵌入其他内容。

任何帮助都将不胜感激。

Answer 1

您可以将var与条件运算符一起使用：

var query = year == "2011" ?
                 from c in _context.Wxlogs
                 where c.LogYear == year 
                 && (SqlFunctions.DatePart("Month", c.LogDate2) == m3) 
                 && c.LogTime.Contains("23:59")
                 orderby c.LogDate2
                 let LogDate = c.LogDate2
                 select new { 
                     LogDate, 
                     c.Rain_today 
                 });
// Second part of conditional
               : from c in _context.Wxlogs
                 where c.LogYear == year 
                 && c.LogMonth == mm 
                 && c.LogTime.Contains("08:59")
                 orderby c.LogDate2
                 let LogDate = EntityFunctions.AddDays(c.LogDate2, -1)
                 select new { 
                     LogDate, 
                     c.Rain_today 
                 });

这不是理想的，但是当你还根据年份更改“LogDate”位时，它可能是最简单的方法 - 两个查询的区别在于提取的地方太多以正常的方式。（这并不像你实际上只是得到了你的标题所暗示的条件“where”条款。）

这里需要var的原因是因为您要投射到匿名类型。如果你不这样做，你可以使用if / else块。你仍然可以这样做，但这有点痛苦。

Answer 2

您无法将new { LogDate, c.Rain_today }强制转换为Wxlog，您需要从这两个查询中返回select c。

如果您只想在最后else之后选择该部分，请输入以下内容

var ra2 = from r in ra
          select new {
              LogDate, 
              c.Rain_today 
          };

Answer 3

尝试（评论后编辑）：

if (year == "2011")
{
ra = (from c in _context.Wxlogs
      where c.LogYear == year && 
            && (SqlFunctions.DatePart("Month", c.LogDate2) == m3) 
            && c.LogTime.Contains("23:59") 
            orderby c.LogDate2
            let LogDate = EntityFunctions.AddDays(c.LogDate2, year == "2011" ? 0 : -1)
            select new { 
                        LogDate, 
                        c.Rain_today 
                        }).AsQueryable();
}
else if (year != "2011")
{
ra = (from c in _context.Wxlogs
      where c.LogYear == year && 
            && c.LogMonth == mm 
            && c.LogTime.Contains("08:59")
            orderby c.LogDate2
            let LogDate = EntityFunctions.AddDays(c.LogDate2, year == "2011" ? 0 : -1)
            select new { 
                        LogDate, 
                        c.Rain_today 
                        }).AsQueryable();
}

LINQ to Entities条件where子句

3 个答案: