从两个相关列表中使用特定条件进行LINQ查询

Question

Using SQL Server and C#: I have 3 tables: Employee ( EmployeeId, JobDescription ), CashAllowance ( CashAllowanceId ) and EmployeeCashAllowance ( EmployeeId, CashAllowanceId, ValueTaken, DateAdded ). Employee has (EmployeeeId) as primary key, CashAllowance has (CashAllowanceId) as primary key, EmployeeCashAllowance has 2 foreign keys (EmployeeId and CashAllowanceId) related to the first 2 tables.

I need to get the list of ( EmployeeCashAllowance ) in a specific date + for specific CashAllowanceId + for employees having JobDescription = "Dev"

I need to achieve this in a LINQ query on lists filled from DB where list of all EmployeeCashAllowance is a property of the Employee object (each Employee object has List ListEmployeeCashAllowances as a property). What I wrote was this:

var sumValues = (from e in Employees
                        where (e.JobDescription == "Dev")
                        from c in e.ListEmployeeCashAllowances
                        where (c.EmployeeId == e.EmployeeId && c.CashAllowanceId == selectedCashAllowanceId && c.DateAdded == selectedDate)
                        select c).ToList();

But this is not working as I expected, it's returning all rows in Employee and EmployeeCashAllowance whatever the selected criteria is (even is JobDescription is not Dev and CashAllowanceId is not the selectedCashAllowanceId).

Where did I go wrong with this?

Answer 1

You better use join I suppose try something like this , I haven't tested so it must look like this

var sumValues = (from e in Employees
                    join c in EmployeeCashAllowances on e.EmployeeId equals c.EmployeeId 
                    where ( c.CashAllowanceId == selectedCashAllowanceId && c.DateAdded == selectedDate && e.JobDescription == "Dev")
                    select c).ToList();

Answer 2

Not Tested, Just gave a try

var results = from e in Employees
              from ec in e.EmployeeCashAllowances
              where (e.EmployeeId == ec.EmployeeId && ec.CashAllowanceId == selectedCashAllowanceId && ec.DateAdded == selectedDate && e.JobDescription == "Dev")
              select ec;

Answer 3

Well, I didn't expect this, but I had to change from the query to get what I want, with the restriction that I had use "Sum" and get sum of values in the list of EmployeeCashAllowance resulted:

Employees.SelectMany(e => e.ListEmployeeCashAllowances).Where(lc => lc.CashAllowanceId == selectedCashAllowanceId).Select(c => c.ValueTaken).Sum();

Note that if I don't use Sum the list returned will contain all items in all the ListEmployeeCashAllowances.

Answer 4

It becomes clear when you clean the formatting:

var sumValues =
    from e in Employees
    where
        e.JobDescription == "Dev"
    from c in e.ListEmployeeCashAllowances // Gotcha!!!
    where
        c.EmployeeId == e.EmployeeId &&    // Is that really necessary?
        c.CashAllowanceId == selectedCashAllowanceId &&
        c.DateAdded == selectedDate
    select c;

Normally I use LINQ methods like:

var query = Employees
    .Where(e => e.JobDescription == "Dev")
    .SelectMany(e => e.ListEmployeeCashAllowances)
    .Where(c =>
        c.CashAllowanceId == selectedCashAllowanceId &&
        c.DateAdded == selectedDate);

But 'e.ListEmployeeCashAllowances' still can be selecting all users... A long shot, without knowing your environment, could be:

var query = Employees
    .SelectMany(e => e.ListEmployeeCashAllowances)
    .Where(c =>
        c.JobDescription == "Dev" &&
        c.CashAllowanceId == selectedCashAllowanceId &&
        c.DateAdded == selectedDate);

Resolving what to do with 'query', you can simply do:

var sumValues = query.Sum(c => c.ValueTaken);