如何使用LINQ的Select/SelectMany提取嵌套列表中的ID

Got it, let's adjust your code to pull just the IDs instead of full employee objects. Here's how to do it with nested Select calls:

var obj = offices.Select(p => new {
    OfficeId = p.Id,
    EmployeeIds = p.Employees.Select(e => e.Id).ToList()
}).ToList();

What's changed? #

• Instead of assigning p.Employees directly (which returns full employee objects), we use p.Employees.Select(e => e.Id) to project each employee to their ID only.
• This keeps your data grouped by office, giving you an anonymous type with each office's ID and a list of corresponding employee IDs.

If you want a flat list instead (no grouping by office): #

If your goal is a single list of (Office ID + Employee ID) pairs rather than grouped collections, use SelectMany to flatten the nested structure:

var flatEmployeeOfficePairs = offices.SelectMany(p => 
    p.Employees.Select(e => new {
        OfficeId = p.Id,
        EmployeeId = e.Id
    })
).ToList();

SelectMany works here by iterating over each office, then each employee in that office, and combining them into a single list of the anonymous type with both IDs.

内容的提问来源于stack exchange，提问作者Marius Kazlauskas