c# - 如何用 lambda 表达式连接 3 个表？

Question

我有一个简单的 LINQ lambda 连接查询，但我想添加一个带有 where 子句的第三个连接。我该怎么做？

这是我的单一连接查询:

var myList = Companies
    .Join(
        Sectors,
        comp => comp.Sector_code,
        sect => sect.Sector_code,
        (comp, sect) => new {Company = comp, Sector = sect} )
    .Select( c => new {
        c.Company.Equity_cusip,
        c.Company.Company_name,
        c.Company.Primary_exchange,
        c.Company.Sector_code,
        c.Sector.Description
    });

我想将以下 SQL 命令添加到上面的 LINQ 查询并仍然保持投影:

SELECT
    sector_code, industry_code 
FROM
    distribution_sector_industry 
WHERE
    service = 'numerical'

第 3 个连接将在 sector_code 上使用 Sector 表和 Distribution_sector_industry 进行。

提前致谢。

Answer 1

只是一个猜测:

var myList = Companies
    .Join(
        Sectors, 
        comp => comp.Sector_code,
        sect => sect.Sector_code,
        (comp, sect) => new { Company = comp, Sector = sect })
    .Join(
        DistributionSectorIndustry.Where(dsi => dsi.Service == "numerical"), 
        cs => cs.Sector.Sector_code,
        dsi => dsi.Sector_code,
        (cs, dsi) => new { cs.Company, cs.Sector, IndustryCode = dsi.Industry_code })
    .Select(c => new {
        c.Company.Equity_cusip,
        c.Company.Company_name,
        c.Company.Primary_exchange,
        c.Company.Sector_code,
        c.Sector.Description,
        c.IndustryCode
});