[英]LINQ-TO-SQL query not working with CSV file
我正在从程序中读取一个简单的csv文件。 这是我的csv文件的样子:
NASDQ,O,
OTC,O,
NYSE,N,
TSE,T,
这是我读取csv文件的代码:
string csvFile = @"x:\tech\SQL_IntlPricing\ExchangeLookup.csv";
string[] csvLines = File.ReadAllLines(csvFile);
var csvValues = csvLines
.Select(l => new {
Exchange = l.Split(',').First(),
Lookup = l.Split(',').Skip(1).First ()});
到目前为止,代码一切正常。 我正在使用以下LINQ查询:
from comp in Companies
where !comp.Coverage_status.Contains("drop")
select new
{
FSTick = string.Format("{0}-{1}", comp.Ticker,
csvValues
.Where(v => v.Exchange.Contains(comp.Exchange))
.Select(v => v.Lookup).FirstOrDefault())
};
但我收到以下错误:
NotSupportedException: Local sequence cannot be used in LINQ to SQL implementations of query operators except the Contains operator.
基本上,我正在尝试获得以下结果:
AAPL-O
MSFT-O
有没有一种方法可以使用LINQ查询获得所需的结果?
如果公司数量不多,那么简单的解决方案将是:
from comp in Companies.Where(c => !c.Coverage_status.Contains("drop")).AsEnumerable()
select new
{
FSTick = string.Format("{0}-{1}", comp.Ticker,
csvValues
.Where(v => v.Exchange.Contains(comp.Exchange))
.Select(v => v.Lookup).FirstOrDefault())
};
否则,您可以像这样进行过滤;
from comp in Companies.Where( c =>
csvValues.Select(cs => cs.Exchange).Contains(comp.Exchange) &&
!c.Coverage_status.Contains("drop")
).AsEnumerable()
select new
{
FSTick = string.Format("{0}-{1}", comp.Ticker,
csvValues
.Where(v => v.Exchange.Contains(comp.Exchange))
.Select(v => v.Lookup).FirstOrDefault())
};
按照我上面的评论,如果将linq-sql表达式转换成其扩展方法语法形式是可以的,则可以执行以下操作:
仅出于示例目的,我创建了公司列表。 公司被定义为
public class Company
{
public string Coverage_status { get; set; }
public string Exchange { get; set; }
public string Ticker { get; set; }
}
这是代码看起来的完整示例:
List<string> csvLines = new List<string>
{
"NASDQ,O,",
"OTC,O,",
"NYSE,N,",
"TSE,T,"
};
var csvValues = csvLines
.Select(l => new
{
Exchange = l.Split(',').First(),
Lookup = l.Split(',').Skip(1).First()
});
List<Company> companies = new List<Company>
{
new Company { Coverage_status = "aaa", Ticker = "123", Exchange = "NASDQ"},
new Company { Coverage_status = "1521drop422", Ticker = "1251223", Exchange = "aaaaaaaa"},
new Company { Coverage_status = "f2hdjjd", Ticker = "15525221123", Exchange = "TSE"}
};
var result = companies
.Where(c => !c.Coverage_status.Contains("drop"))
.Select(n => new
{
FSTick = string.Format("{0}-{1}", n.Ticker,
csvValues
.Where(v => v.Exchange.Contains(n.Exchange))
.Select(v => v.Lookup).FirstOrDefault())
});
foreach (var r in result)
Console.WriteLine(r.FSTick);
出于记录,此代码绝对不是性能方面的。
输出:
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