LINQ JOIN具有3个表，其中两个表具有多对一关系

Question

Hy. I'm working on a query, which should join 3 tables like

• client - has ID - take his name
• banking - has clientid - take some data from bankDate to bankDate
• marketing - has clientid - take some data from marketDate to marketDate

code:

var totals = from client in _db.Clients
                join bank in _db.Banking on client.Id equals bank.ClientId
                where (client.Id == bank.ClientId  &&
                       DateTime.Compare(bank.BankDate, (DateTime) fromDate) >= 0 &&
                       DateTime.Compare(bank.BankDate, (DateTime) toDate) <= 0)
                join market in _db.Marketing on client.Id equals market.ClientId
                where (client.Id == market.ClientId && 
                       DateTime.Compare(market.MarketDate, (DateTime) fromDate) >= 0 &&
                       DateTime.Compare(market.MarketDate, (DateTime) toDate) <= 0)
                select new {client.Username, bank, market};

This algorithm doesn't provide successful join for the tables with many-to-one relations. Who has ever faced this problem and knows how to solve it? I'll be very appreciated for any help

Answer 1

I am assuming that the where statement is not referencing the correct table.

Try this: (might be syntax error)

var totals = from client in _db.Clients
        join bank in _db.Banking.Where(x => DateTime.Compare(x.BankDate, (DateTime) fromDate) >= 0 &&
                DateTime.Compare(x.BankDate, (DateTime) toDate) <= 0) on client.Id equals bank.ClientId
        join market in _db.Marketing.Where(x => DateTime.Compare(x.MarketDate, (DateTime) fromDate) >= 0 &&
                DateTime.Compare(x.MarketDate, (DateTime) toDate) <= 0) on client.Id equals market.ClientId
        select new {client.Username, bank, market};

Answer 2

By many-to-one I guess you are looking for left outer join, try this.

var totals = from client in _db.Clients
                         join bank in _db.Banking on client.Id equals bank.ClientId into banks
                         from bank in banks.DefaultIfEmpty()
                         where (client.Id == bank.ClientId &&
                                DateTime.Compare(bank.BankDate, (DateTime)fromDate) >= 0 &&
                                DateTime.Compare(bank.BankDate, (DateTime)toDate) <= 0)
                         join market in _db.Marketing on client.Id equals market.ClientId into markets
                         from market in markets.DefaultIfEmpty()
                         where (client.Id == market.ClientId &&
                                DateTime.Compare(market.MarketDate, (DateTime)fromDate) >= 0 &&
                                DateTime.Compare(market.MarketDate, (DateTime)toDate) <= 0)
                         select new { client.Username, bank, market };