如何将该SQL查询转换为LINQ？

Question

如何将该SQL查询转换为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

到目前为止，我已经提出了这一行：

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达式来添加'bi.MonthlyBudgetItem = 1'。

有人有主意吗？

编辑1：我忘了提及实体之间的关系。 每个ExpenseGroup都有很多费用 ，每个Expense都有很多BudgetItems 。

因此，ExpenseGroup => Expenses => BudgetItems

编辑2：我使用的是Entity Framework，每个ExpenseGroup都有一个Expense对象的集合（每个Expense都有一个ExpenseGroup对象），每个Expense都有一个BudgetItem对象的集合（每个BudgetItem对象都有一个Expense对象）。

Answer 1

我想应该这样做：

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

与此类似...

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

您实际上是在SQL查询中进行inner join联接，因此在linq查询中也是如此。 这应该工作：

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)
                   };