如何將該SQL查詢轉換為LINQ？

Question

如何將該SQL查詢轉換為LINQ？

SELECT eg.Name Name, sum(bi.PlannedAmount) Amount
FROM BudgetItem bi, Expense e, ExpenseGroup eg
WHERE Discriminator = 'ExpenseItem' AND
bi.ExpenseId = e.Id AND
e.ExpenseGroupId = eg.id AND
bi.MonthlyBudgetId = 1
GROUP BY eg.Name

到目前為止，我已經提出了這一行：

var result = context
            .ExpenseGroups
            .GroupBy(eg => eg.Id, (s) => new { Name = s.Name, Amount = s.Expenses.SelectMany(e => e.Items).Sum(i => i.PlannedAmount) })
            .ToList();

但是我仍然不知道要使用什么表達式來添加'bi.MonthlyBudgetItem = 1'。

有人有主意嗎？

編輯1：我忘了提及實體之間的關系。 每個ExpenseGroup都有很多費用 ，每個Expense都有很多BudgetItems 。

因此，ExpenseGroup => Expenses => BudgetItems

編輯2：我使用的是Entity Framework，每個ExpenseGroup都有一個Expense對象的集合（每個Expense都有一個ExpenseGroup對象），每個Expense都有一個BudgetItem對象的集合（每個BudgetItem對象都有一個Expense對象）。

Answer 1

我想應該這樣做：

var result = context
        .ExpenseGroups
        .Where(x => x.Discriminator == 'ExpenseItem' && 
            x.bi.ExpenseId == e.Id && 
            x.e.ExpenseGroupId == eg.id &&
            x.bi.MonthlyBudgetId == 1)
        .GroupBy(eg => eg.Id, (s) => new { Name = s.Name, Amount = s.Expenses.SelectMany(e => e.Items).Sum(i => i.PlannedAmount) })
        .ToList();

Answer 2

與此類似...

var result = (from g in context.ExpenseGroups
              where g.Expense.BudgetItem.MonthlyBudgetId == 1
              select g)
        .GroupBy(eg => eg.Id, (s) => new { Name = s.Name, Amount = s.Expenses.SelectMany(e => e.Items).Sum(i => i.PlannedAmount) })
        .ToList();

要么

var result = context.ExpenseGroups
             .Where(g => g.Expense.BudgetItem.MonthlyBudgetId == 1)
             .GroupBy(eg => eg.Id, (s) => new { Name = s.Name, Amount = s.Expenses.SelectMany(e => e.Items).Sum(i => i.PlannedAmount) })
        .ToList();

Answer 3

您實際上是在SQL查詢中進行inner join聯接，因此在linq查詢中也是如此。 這應該工作：

var result = from bi in context.BudgetItem
             join e in context.Expense 
             on bi.ExpenseId equals e.Id 
             where bi.MonthlyBudgetId == 1
             join eg in ExpenseGroup 
             on e.ExpenseGroupId equals eg.id 
             group new { bi, eg } by eg.Name into g
             select new 
                   {
                         Name = g.Key,
                         Amount = g.Sum(x => x.bi.PlannedAmount)
                   };