Question

这很好。g.Key不为空并且有适当的数据：

var result = db.JournalEntries.Include(je => je.JournalRecords.Select(jr => jr.Account).Select(j => j.AccountParticulars))
                .Where(je => je.Date >= existingLedgerTransaction.From && je.Date <= existingLedgerTransaction.To)
                .SelectMany(s => s.JournalRecords)
                .GroupBy(d => d.AccountParticular.Account.AccountCategory)
                .Select(g => new { Name = g.Key.Name });

但是这不起作用，因为g.Key为null：

var DateFilter = new Func<JournalEntry, bool>(je => je.Date >= existingLedgerTransaction.From && je.Date <= existingLedgerTransaction.To);

var result = db.JournalEntries.Include(je => je.JournalRecords.Select(jr => jr.Account).Select(j => j.AccountParticulars))
                .Where(DateFilter)
                .SelectMany(s => s.JournalRecords)
                .GroupBy(d => d.AccountParticular.Account.AccountCategory)
                .Select(g => new { Name = g.Key.Name });

我在一个带有静态集合的简单控制台应用程序中尝试了同样的事情，并且传入谓词工作正常。这可能是什么问题？

注意：禁用延迟加载/动态代理

Answer 1

尝试

 var DateFilter = new Expression<Func<JournalEntry, bool>>(je => je.Date >= existingLedgerTransaction.From && je.Date <= existingLedgerTransaction.To);

因为您需要将表达式树传递给EF

Linq GroupBy With Passed Where Predicate

1 个答案: