Question

我的情况，见下图：

我设计了一个查询并添加了分组，但分组并没有将记录减少到最年轻的ContractEndDate。它似乎对结果没有影响。

public IQueryable<SoonObsoleteContractsViewModel> Get()
    {

var countries = UnitOfWork.GetAll<Country>();
var companies = UnitOfWork.GetAll<Company>();
var contracts = UnitOfWork.GetAll<Contract>();

var query = from country in countries
            join company in companies on country.Id equals company.CountryId
            join contract in contracts on company.Id equals contract.CompanyId

            select new SoonObsoleteContractsViewModel
            {
                CountryName = contry.Name,
                CompanyName = company.Name,
                CompanyId = company.CompanyId
                ContractBeginDate = contract.Begin,
                ContractEndDate = contract.End,
                ContractId = contract.Id
            };

            query.GroupBy(c => c.CompanyId, (key, e) => e.OrderBy(f => f.ContractEndDate).First());
        return query;
    }

任何帮助都将不胜感激。

Answer 1

按国家/地区和公司分组，然后获取具有最近合同结束日期的组中的记录。

var result = query
             .GroupBy(_ => new { _.CountryName, _.CompanyId})
             .Select(g => g.OrderByDescending(c => c.ContractEndDate).First())
             .ToList();

或换句话说

var query = from contry in countries
            join company in companies on country.Id equals company.CountryId
            join contract in contracts on company.Id equals contract.CompanyId
            let viewModel = new SoonObsoleteContractsViewModel
            {
                CountryName = contry.Name,
                CompanyName = company.Name,
                CompanyId = company.CompanyId
                ContractBeginDate = contract.Begin,
                ContractEndDate = contract.End,
                ContractId = contract.Id
            }
            group viewModel by new { viewModel.CountryName, viewModel.CompanyId } into g
            select g.OrderByDescending(c => c.ContractEndDate).First();

Answer 2

感谢NKosi，我终于解决了它：

var query = from contry in countries
        join company in companies on country.Id equals company.CountryId
        join contract in contracts on company.Id equals contract.CompanyId
        let viewModel = new SoonObsoleteContractsViewModel
        {
            CountryName = contry.Name,
            CompanyName = company.Name,
            CompanyId = company.CompanyId
            ContractBeginDate = contract.Begin,
            ContractEndDate = contract.End,
            ContractId = contract.Id
        }
        group viewModel by new { viewModel.CountryName, viewModel.CompanyId } into g
        select g.OrderByDescending(c => c.ContractEndDate).FirstOrDefault();

我所要做的只是将 First（）更改为 FirstOrDefault ！否则，查询将生成一个空列表。

Linq查询与分组以获取最年轻的日期

2 个答案: