c# - 使用LINQ比较两个列表

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我有三个列表，BeforeList，AfterList和FinalList

BeforeList具有以下值

ID Description Operation
1  Descr1      Null
2  Descr2      Null
3  Descr3      Null

AfterList具有以下值

ID Description Operation
1  Descr1      Null
2  DescrC      Null
4  Descr4      Null

我的FinalList将是

ID Description Operation
1  Descr1      Null
2  DescrC      Update
3  Descr3      Delete
4  Descr4      Add

如何使用LINQ获取FinalList

最佳答案

怎么样：

var beforeListById = beforeList.ToDictionary(item => item.Id);
var afterListById = afterList.ToDictionary(item => item.Id);

var finalResult = from id in beforeListById.Keys.Union(afterListById.Keys)

                  let before = beforeListById.ContainsKey(id) ? beforeListById[id] : null
                  let after = afterListById.ContainsKey(id) ? afterListById[id] : null

                  select new Record
                  {
                      Id = id,
                      Description = (after ?? before).Description,
                      Operation = (before != null && after != null)
                                   ? (after.Description == before.Description ? "Null" : "Update")
                                   : (after != null) ? "Add" : "Delete"
                  };

编辑：使查询更简单（假设项目为非null）。